A/C and/or condenser fan issues
08-11-2014, 01:57 PM
#1
6th Gear
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A/C and/or condenser fan issues
The Patient: 1988 35th Anniversary Corvette, 4+3 transmission.
I’ve read several forum topics regarding the cooling fan operations. If I understand correctly, there are two fans, one located in front of the condenser (I’ll call it the “condenser fan”) and one behind the radiator, between the radiator and the engine (I’ll call this one the “radiator fan”). I have auto-temp control A/C.
1) Is the condenser fan supposed to activate as soon as the A/C function is turned to cool?
2) Is the condenser fan continuously on during A/C operations?
3) Is there any interaction between the A/C function and the radiator fan? Should it come on when the A/C pressure gets high – as an assist to the condenser fan?
I have had a new radiator installed, which reduced the on-highway operating temperature to 185 – 200 with outside air temp of 90+. Even in heavy stop and go traffic on 90 degree days, the engine operating temp rarely goes above 220 degrees. This is without A/C operating.
With A/C operating, the on-highway, engine temp stays above 190 and when stopped it will quickly go to 220+ on my 90+ degree days.
Recently, after being at idle (in neutral or clutch in) and while stopped, the engine seems to bog down like the A/C compressor is dragging down the RPMs. If I switch off the A/C, the engine returns to normal idle speed and is very responsive.
My suspicion is that the condenser fan is not continuously operating when A/C is on, and the head pressure is building sufficiently to almost seize the compressor – hence dragging the engine RMPs down.
Any suggestions as to how to check the fan operations or point to any other trouble shooting checks that should be performed, would be greatly appreciated.
Jim S.
I’ve read several forum topics regarding the cooling fan operations. If I understand correctly, there are two fans, one located in front of the condenser (I’ll call it the “condenser fan”) and one behind the radiator, between the radiator and the engine (I’ll call this one the “radiator fan”). I have auto-temp control A/C.
1) Is the condenser fan supposed to activate as soon as the A/C function is turned to cool?
2) Is the condenser fan continuously on during A/C operations?
3) Is there any interaction between the A/C function and the radiator fan? Should it come on when the A/C pressure gets high – as an assist to the condenser fan?
I have had a new radiator installed, which reduced the on-highway operating temperature to 185 – 200 with outside air temp of 90+. Even in heavy stop and go traffic on 90 degree days, the engine operating temp rarely goes above 220 degrees. This is without A/C operating.
With A/C operating, the on-highway, engine temp stays above 190 and when stopped it will quickly go to 220+ on my 90+ degree days.
Recently, after being at idle (in neutral or clutch in) and while stopped, the engine seems to bog down like the A/C compressor is dragging down the RPMs. If I switch off the A/C, the engine returns to normal idle speed and is very responsive.
My suspicion is that the condenser fan is not continuously operating when A/C is on, and the head pressure is building sufficiently to almost seize the compressor – hence dragging the engine RMPs down.
Any suggestions as to how to check the fan operations or point to any other trouble shooting checks that should be performed, would be greatly appreciated.
Jim S.
08-11-2014, 03:06 PM
#2
Burning Brakes
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When u turn on the A/C yes the condenser fan should come on at the same time the compressor engages and I think but I'm not sure the radiator fan should also come on.
If there isn't any airflow across the condenser while the compressor is running the high side will always quickly rise and the compressor will be cut off. So you need to make sure ur fans are working and coming on.
Also the stock single core radiator fan was designed with a lot more fins per inch than a normal radiator so the single core can be effective and the nose of your Vette is like a vacuum cleaner and sucks up everything in the condenser and radiator. It all needs to be cleaned out to be effective.
Also a good flush is due if not done and I would start with adding some cleaner mild acid and running it for a few days then power flushing the system with the knock sensors removed. Also checking the fluid with a volt meter will tell ya if its needed because the fluid collects metals and that can be measured and if high and left long enough with cause damage to other metals and senors and gaskts. Their is a lot on the net if u want to research this. Here is just one video on how to exactly measure for this with a volt meter
If there isn't any airflow across the condenser while the compressor is running the high side will always quickly rise and the compressor will be cut off. So you need to make sure ur fans are working and coming on.
Also the stock single core radiator fan was designed with a lot more fins per inch than a normal radiator so the single core can be effective and the nose of your Vette is like a vacuum cleaner and sucks up everything in the condenser and radiator. It all needs to be cleaned out to be effective.
Also a good flush is due if not done and I would start with adding some cleaner mild acid and running it for a few days then power flushing the system with the knock sensors removed. Also checking the fluid with a volt meter will tell ya if its needed because the fluid collects metals and that can be measured and if high and left long enough with cause damage to other metals and senors and gaskts. Their is a lot on the net if u want to research this. Here is just one video on how to exactly measure for this with a volt meter
08-11-2014, 05:30 PM
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When u turn on the A/C yes the condenser fan should come on at the same time the compressor engages and I think but I'm not sure the radiator fan should also come on.
If there isn't any airflow across the condenser while the compressor is running the high side will always quickly rise and the compressor will be cut off. So you need to make sure ur fans are working and coming on.
Also the stock single core radiator fan was designed with a lot more fins per inch than a normal radiator so the single core can be effective and the nose of your Vette is like a vacuum cleaner and sucks up everything in the condenser and radiator. It all needs to be cleaned out to be effective.
Also a good flush is due if not done and I would start with adding some cleaner mild acid and running it for a few days then power flushing the system with the knock sensors removed. Also checking the fluid with a volt meter will tell ya if its needed because the fluid collects metals and that can be measured and if high and left long enough with cause damage to other metals and senors and gaskts. Their is a lot on the net if u want to research this. Here is just one video on how to exactly measure for this with a volt meter
Antifreeze coolant Checking with a Multimeter (updated) - YouTube
If there isn't any airflow across the condenser while the compressor is running the high side will always quickly rise and the compressor will be cut off. So you need to make sure ur fans are working and coming on.
Also the stock single core radiator fan was designed with a lot more fins per inch than a normal radiator so the single core can be effective and the nose of your Vette is like a vacuum cleaner and sucks up everything in the condenser and radiator. It all needs to be cleaned out to be effective.
Also a good flush is due if not done and I would start with adding some cleaner mild acid and running it for a few days then power flushing the system with the knock sensors removed. Also checking the fluid with a volt meter will tell ya if its needed because the fluid collects metals and that can be measured and if high and left long enough with cause damage to other metals and senors and gaskts. Their is a lot on the net if u want to research this. Here is just one video on how to exactly measure for this with a volt meter
Antifreeze coolant Checking with a Multimeter (updated) - YouTube
Thanks for your reply.
Rest assured, when the radiator was replaced by an ASE Certified Mechanic, the whole engine cooling system was power flushed. I installed new water pump and thermostat. (I do not know how old the water pump was, so it was replaced as a precaution.)
The engine cooling system is functioning just fine.
My question is specifically regarding the condenser fan (you answered it comes on when the A/C is turned on) but I still need an answer about the radiator fan - is it also triggered by a high side overpressure? I know the compressor clutch is supposed to disengage if the high side pressure reaches 400 psi, but I don't know about the radiator fan's function - is it also triggered by a high side pressure, or controlled only by engine coolant temperature.
Jim S.
08-11-2014, 07:14 PM
#4
Do you have the FSM for your car? The AUX fan in an '88 has dual control for 'ON'. There's a temperature switch set at 228° and then the AC pressure switch set at I believe 240 PSI. The AC pressure switch signal is sent to the ECM and the ECM controls the AUX fan when AC ON. The temp switch is an over ride for the AUX fan.
OOPS - I overlooked the wiring schematic when checking and the option for B4P. Dave "HookedonVettes" fixed it though.
OOPS - I overlooked the wiring schematic when checking and the option for B4P. Dave "HookedonVettes" fixed it though.
Last edited by WVZR-1; 08-11-2014 at 08:13 PM.
08-11-2014, 08:00 PM
#7
Melting Slicks
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The fan in front of the condenser was an option called B4P.
It is operated by a fan switch that shorts out at around 228F.
The fan temperature switch is screwed into the head
between spark plugs 1 and 3. It is not controlled by the ECM or AC system.
The radiator fan is controlled by the ECM. It monitors the engine
coolant temperature sensor which is screwed into the front edge of
the intake manifold.
The ECM will turn on the radiator fan at around 226F.
The ECM will also turn on the radiator fan when the AC coolant fan
switch pressure reaches 233 psi and off at around 185 psi. This
assumes the engine temperature is below 226F.
There is a AC high pressure cut off switch that will turn off the AC
compressor clutch when high pressure reaches 430 psi and back on at
200 psi. This is done by the HVAC control head if you have C68 auto
climate control.
If you have 60 manual AC the AC high pressure cut off switch is in series with the power to the AC clutch coil.
The first diagram shows the location of the AC coolant fan switch
and the high pressure cut off switch. The physical position of them can
be reversed so you have to go by the color of the wires at the connector.
It is operated by a fan switch that shorts out at around 228F.
The fan temperature switch is screwed into the head
between spark plugs 1 and 3. It is not controlled by the ECM or AC system.
The radiator fan is controlled by the ECM. It monitors the engine
coolant temperature sensor which is screwed into the front edge of
the intake manifold.
The ECM will turn on the radiator fan at around 226F.
The ECM will also turn on the radiator fan when the AC coolant fan
switch pressure reaches 233 psi and off at around 185 psi. This
assumes the engine temperature is below 226F.
There is a AC high pressure cut off switch that will turn off the AC
compressor clutch when high pressure reaches 430 psi and back on at
200 psi. This is done by the HVAC control head if you have C68 auto
climate control.
If you have 60 manual AC the AC high pressure cut off switch is in series with the power to the AC clutch coil.
The first diagram shows the location of the AC coolant fan switch
and the high pressure cut off switch. The physical position of them can
be reversed so you have to go by the color of the wires at the connector.
08-12-2014, 01:54 AM
#9
Race Director
The fan in front of the condenser was an option called B4P.
It is operated by a fan switch that shorts out at around 228F.
The fan temperature switch is screwed into the head
between spark plugs 1 and 3. It is not controlled by the ECM or AC system.
The radiator fan is controlled by the ECM. It monitors the engine
coolant temperature sensor which is screwed into the front edge of
the intake manifold.
The ECM will turn on the radiator fan at around 226F.
It is operated by a fan switch that shorts out at around 228F.
The fan temperature switch is screwed into the head
between spark plugs 1 and 3. It is not controlled by the ECM or AC system.
The radiator fan is controlled by the ECM. It monitors the engine
coolant temperature sensor which is screwed into the front edge of
the intake manifold.
The ECM will turn on the radiator fan at around 226F.
Some people like the auxiliary fan to come on at a lower temperature and you can buy thermal switches with lower temperature set points.
08-12-2014, 07:06 AM
#10
6th Gear
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The auxiliary fan turns on at 238°F. You can test it by disconnecting the connector from the temperature switch between spark plugs #1 and #3 and grounding the connector. There is a relay for this fan on the front of the fan shroud on the driver's side.
Some people like the auxiliary fan to come on at a lower temperature and you can buy thermal switches with lower temperature set points.
Some people like the auxiliary fan to come on at a lower temperature and you can buy thermal switches with lower temperature set points.
Here is a summary of what I believe is the consensus of opinions as to the “triggers” for each fan’s operation, and my questions about troubleshooting all of the switch / fan functions.
The condenser fan (located in front of the condenser) is controlled by a temperature switch screwed into the cylinder head between spark plugs 1 and 3. It has no ECM connection and is pure temperature sensitive. Activates at 238F.
[Cliff Harris posts that I can buy a thermal switch with a lower temperature set point. He also says that to troubleshoot, disconnect the connector from the temperature switch and ground the connector. I assume the fan should activate upon grounding? I live in Houston (never gets hot here) so I am interested in obtaining a lower temperature thermal switch – anyone have a brand and/or part number for a 200F switch?]
The radiator fan (between the radiator and engine) is controlled by 1) the ECM through a temperature switch screwed in the front edge of the intake manifold [activates at 226F], and 2) an A/C coolant switch functioning through the ECM, which will turn on the radiator fan when the A/C coolant pressure reaches 223 psi, and off at around 185psi, regardless of engine coolant temperature.
[Is there a simple troubleshooting procedure to check the proper function of the A/C coolant switch? Since it works in conjunction with the ECM – does the switch send voltage to the ECM to activate the radiator fan or does the switch cease to send a signal to the ECM so that the ECM will activate the radiator fan?]
The A/C high pressure cut off switch will disengage the compressor clutch when a high pressure of 430psi is reached, and then reengage the compressor clutch at around 200 psi. This switch functions through the C68 auto climate control head.
[My C68 climate control head is OEM – 26 years old. Is there a troubleshooting procedure to check the function of the high pressure cut off switch to make sure the switch and C68 control head functions properly and they disengage the compressor clutch upon a high pressure trigger?]
To repeat my symptoms – when the engine is first started (cool engine) and then turn on the A/C, I get cold air within seconds, I have no idle issues (only slight drop in RPM when A/C engaged). This holds true for the first few minutes of operation. After driving for several minutes at normal engine operating temperature, I can come to a stop and the engine will bog down, and sometimes actually die. If I am quick, I can turn off the A/C and the engine RPMs return to normal, no bogging down and it is responsive. Once back at highway speeds, I can turn the A/C back on and everything seems to work fine.
My thoughts are that I may have more than one issue. The condenser fan and/or radiator fan are not functioning properly while at a stop and the engine has been running at normal operating temp for several minutes. The dash digital temperature gauge indicates a fairly rapid temperature rise while at idle, and this is when I have the bogging down issues. Since replacing the radiator, water pump and thermostat, with A/C running, I have not seen temps above 220F. However, the engine’s bogging down starts around 210F to 215F. My uneducated guess is that I am getting a high pressure A/C problem that is making the compressor labor, thus dragging the engine RPMs down. Is this caused by lack of timely radiator fan operation, a high pressure cut off switch not properly functioning, or all or none of the above?
Thank you all for your responses – this has me scratchin’ my head!
Last edited by JHStevenson; 08-12-2014 at 07:12 AM.
08-12-2014, 11:23 AM
#11
Melting Slicks
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If this car is new to you?
The front optional condenser fan does nothing. I wouldn't waste money
on buying a lower temperature switch.
The idle problem with the AC on could be something as simple as a dirty IAC and throttle body.
People have always complained about the temp. rising with AC on
when the vehicle is not moving on the older C4's. In 1990 GM
started using two radiator fans and tilted the condenser and radiator.
You don't hear many complaints about the engine temps on those vehicles.
Are you positive you have R12 in the system?
Has it been converted to 134A which uses screw on quick couple type fittings?
Purchase a set of AC manifold gauges. Make sure you get a set that can do both R12 and R134A. If you're using R12 you need a high side adapter that converts 1/4 to 3/16.
The 89 has the same AC system as a 88. The Helms service manual on one page lists the refrigerant capacity as 2.25 lbs. On a different page it says 2.75 lbs. In a 90 service manual it says 2.25 lbs. I'd go with the 2.25 lbs.
To check the AC Coolant fan switch monitor the AC high side pressure. The radiator fan should come on around 233 psi and off at 185. On another page of the service manual it says on at 240 off at 190.
No way of testing the high pressure cut off switch.
Below is a performance chart you can use to verify your pressures are in the ball park.
The last photo shows the page in the service manual showing 2.25 lbs. of refrigerant.
The front optional condenser fan does nothing. I wouldn't waste money
on buying a lower temperature switch.
The idle problem with the AC on could be something as simple as a dirty IAC and throttle body.
People have always complained about the temp. rising with AC on
when the vehicle is not moving on the older C4's. In 1990 GM
started using two radiator fans and tilted the condenser and radiator.
You don't hear many complaints about the engine temps on those vehicles.
Are you positive you have R12 in the system?
Has it been converted to 134A which uses screw on quick couple type fittings?
Purchase a set of AC manifold gauges. Make sure you get a set that can do both R12 and R134A. If you're using R12 you need a high side adapter that converts 1/4 to 3/16.
The 89 has the same AC system as a 88. The Helms service manual on one page lists the refrigerant capacity as 2.25 lbs. On a different page it says 2.75 lbs. In a 90 service manual it says 2.25 lbs. I'd go with the 2.25 lbs.
To check the AC Coolant fan switch monitor the AC high side pressure. The radiator fan should come on around 233 psi and off at 185. On another page of the service manual it says on at 240 off at 190.
No way of testing the high pressure cut off switch.
Below is a performance chart you can use to verify your pressures are in the ball park.
The last photo shows the page in the service manual showing 2.25 lbs. of refrigerant.
Last edited by Hooked on Vettes; 08-12-2014 at 11:32 AM.
08-12-2014, 11:49 AM
#12
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If this car is new to you?
The front optional condenser fan does nothing. I wouldn't waste money
on buying a lower temperature switch.
The idle problem with the AC on could be something as simple as a dirty IAC and throttle body.
People have always complained about the temp. rising with AC on
when the vehicle is not moving on the older C4's. In 1990 GM
started using two radiator fans and you don't hear many complaints about the engine temps.
Are you positive you have R12 in the system?
Has it been converted to 134A which uses screw on quick couple type fittings?
Purchase a set of AC manifold gauges. Make sure you get a set that can do both R12 and R134A. If you're using R12 you need a high side adapter that converts 1/4 to 3/16.
The 89 has the same AC system as a 88. The Helms service manual on one page lists the refrigerant capacity as 2.25 lbs. On a different page it says 2.75 lbs. In a 90 service manual it says 2.25 lbs. I'd go with the 2.25 lbs.
To check the AC Coolant fan switch monitor the AC high side pressure. The radiator fan should come on around 233 psi and off at 185. On another page of the service manual it says on at 240 off at 190.
No way of testing the high pressure cut off switch.
Below is a performance chart you can use to verify your pressures are in the ball park.
The last photo shows the page in the service manual showing 2.25 lbs. of refrigerant.
The front optional condenser fan does nothing. I wouldn't waste money
on buying a lower temperature switch.
The idle problem with the AC on could be something as simple as a dirty IAC and throttle body.
People have always complained about the temp. rising with AC on
when the vehicle is not moving on the older C4's. In 1990 GM
started using two radiator fans and you don't hear many complaints about the engine temps.
Are you positive you have R12 in the system?
Has it been converted to 134A which uses screw on quick couple type fittings?
Purchase a set of AC manifold gauges. Make sure you get a set that can do both R12 and R134A. If you're using R12 you need a high side adapter that converts 1/4 to 3/16.
The 89 has the same AC system as a 88. The Helms service manual on one page lists the refrigerant capacity as 2.25 lbs. On a different page it says 2.75 lbs. In a 90 service manual it says 2.25 lbs. I'd go with the 2.25 lbs.
To check the AC Coolant fan switch monitor the AC high side pressure. The radiator fan should come on around 233 psi and off at 185. On another page of the service manual it says on at 240 off at 190.
No way of testing the high pressure cut off switch.
Below is a performance chart you can use to verify your pressures are in the ball park.
The last photo shows the page in the service manual showing 2.25 lbs. of refrigerant.
My young friend of many years, an ASE certified everything (including heating and A/C), now has the car. Says that operating pressures are within spec, naturally it would be when in his shop. He drove the car and has now experienced the described symptoms.
I provided him this forum link - he will have lots of good information to work with.
I will post what the cure turns out to be.
Thanks all!
08-13-2014, 12:51 AM
#13
Race Director
The radiator fan (between the radiator and engine) is controlled by 1) the ECM through a temperature switch screwed in the front edge of the intake manifold [activates at 226F], and 2) an A/C coolant switch functioning through the ECM, which will turn on the radiator fan when the A/C coolant pressure reaches 223 psi, and off at around 185psi, regardless of engine coolant temperature.
[Is there a simple troubleshooting procedure to check the proper function of the A/C coolant switch? Since it works in conjunction with the ECM – does the switch send voltage to the ECM to activate the radiator fan or does the switch cease to send a signal to the ECM so that the ECM will activate the radiator fan?]
[Is there a simple troubleshooting procedure to check the proper function of the A/C coolant switch? Since it works in conjunction with the ECM – does the switch send voltage to the ECM to activate the radiator fan or does the switch cease to send a signal to the ECM so that the ECM will activate the radiator fan?]
This switch is on the left in this picture (the one with the small connector):
08-16-2014, 06:17 AM
#14
6th Gear
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[QUOTE=JHStevenson;1587576768]I have had the car for about 3 years. It was converted to 134a shortly after I purchased it - the A/C was not working when purchased. I have had no issues with the A/C since then, no added 134a, no nothing - had been performing like champ.
My young friend of many years, an ASE certified everything (including heating and A/C), now has the car. Says that operating pressures are within spec, naturally it would be when in his shop. He drove the car and has now experienced the described symptoms.
I provided him this forum link - he will have lots of good information to work with.
I will post what the cure turns out to be.
+++++++
Thanks for all of the help... as it turns out, I had two (or three) problems that together caused the engine RPMs to drop.
Both of the high side switches were periodically malfunctioning as was the low pressure clutch cycling switch. Why all three managed to fail simultaneously is mainly attributable to ancient parts and connectors. So, when the "perfect storm" of all three failing to perform, here is what happened.
1) the RPM drop was because the ECM was not being notified that the A/C was on, hence there was no signal to the IAC to compensate for the compressor drag.
2) The A/C Coolant Fan Switch worked when it felt like it. With gauges on, high-side pressure would build and sometimes engage the radiator fan, and at other times pressure would continue to rise (no fan) to nearly 400. He would turn off the A/C and everything returned to normal operation. He would then try again, and the A/C coolant fan switch would engage the radiator fan - (Switch and connector replaced.)
3) On one occasion, he was not quick enough to turn the A/C off and saw pressure go well above the 433 clutch cut-off pressure. (Switch and connector replaced)
I know he also replaced the low-side pressure cycling switch (and connector), but I can't recall if this was the culprit for the ECM non-notification or it was the A/C coolant fan switch.
Bottom line, three test drives in 95 degree temperatures, and I now have no RPM problems at a stop and at idle, I have ice cold A/C and I am a happy camper.
On one of the longer test drives, he noted that the Cruise Control was not working. It took him about three minutes to find that the vacuum hose to the clutch/brake pedal switch assembly was rotten, and had broken. He ran a new hose, and I now have Cruise Control - no charge!
I have been able to fix a number of small problems over the last three years because of the questions and answers posted on this forum. I do not wish my A/C and RPM problems on anyone else, but hopefully this might be helpful to someone down the line.
Thanks all - I really appreciate the time you took responding and offering suggestions.
Regards,
Jim
My young friend of many years, an ASE certified everything (including heating and A/C), now has the car. Says that operating pressures are within spec, naturally it would be when in his shop. He drove the car and has now experienced the described symptoms.
I provided him this forum link - he will have lots of good information to work with.
I will post what the cure turns out to be.
+++++++
Thanks for all of the help... as it turns out, I had two (or three) problems that together caused the engine RPMs to drop.
Both of the high side switches were periodically malfunctioning as was the low pressure clutch cycling switch. Why all three managed to fail simultaneously is mainly attributable to ancient parts and connectors. So, when the "perfect storm" of all three failing to perform, here is what happened.
1) the RPM drop was because the ECM was not being notified that the A/C was on, hence there was no signal to the IAC to compensate for the compressor drag.
2) The A/C Coolant Fan Switch worked when it felt like it. With gauges on, high-side pressure would build and sometimes engage the radiator fan, and at other times pressure would continue to rise (no fan) to nearly 400. He would turn off the A/C and everything returned to normal operation. He would then try again, and the A/C coolant fan switch would engage the radiator fan - (Switch and connector replaced.)
3) On one occasion, he was not quick enough to turn the A/C off and saw pressure go well above the 433 clutch cut-off pressure. (Switch and connector replaced)
I know he also replaced the low-side pressure cycling switch (and connector), but I can't recall if this was the culprit for the ECM non-notification or it was the A/C coolant fan switch.
Bottom line, three test drives in 95 degree temperatures, and I now have no RPM problems at a stop and at idle, I have ice cold A/C and I am a happy camper.
On one of the longer test drives, he noted that the Cruise Control was not working. It took him about three minutes to find that the vacuum hose to the clutch/brake pedal switch assembly was rotten, and had broken. He ran a new hose, and I now have Cruise Control - no charge!
I have been able to fix a number of small problems over the last three years because of the questions and answers posted on this forum. I do not wish my A/C and RPM problems on anyone else, but hopefully this might be helpful to someone down the line.
Thanks all - I really appreciate the time you took responding and offering suggestions.
Regards,
Jim
Last edited by JHStevenson; 08-16-2014 at 06:22 AM.
08-16-2014, 09:58 AM
#16
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08-16-2014, 10:14 AM
#17
Instructor
Yes, I have an 85 and recently went through A/C pressure switch/sensor investigation as well. Those factory service manuals are great, and you can get some very good advice on this forum.