A/C compressor won't cycle
Thread Starter
Racer
Joined: Apr 2002
Posts: 389
Likes: 0
From: Micco FL
A/C compressor won't cycle
Background: 1992, LT1 with C68 (electronic air); Brand new compressor, R134, dryer, etc.; New ECM; NO error codes on anything.
Symptoms: #1 Compressor won't cycle when A/C on, regardless of what the temp is set at; #2 A/C blows cold for 30 seconds, hot for 5 seconds, continues this cycle until A/C is turned off; #3 when using the vent it blows ambient for for 30 seconds and hot for 5 seconds.
Have a new A/C programmer in hand and wondered if it might be something else.
Ideas?
Symptoms: #1 Compressor won't cycle when A/C on, regardless of what the temp is set at; #2 A/C blows cold for 30 seconds, hot for 5 seconds, continues this cycle until A/C is turned off; #3 when using the vent it blows ambient for for 30 seconds and hot for 5 seconds.
Have a new A/C programmer in hand and wondered if it might be something else.
Ideas?
Le Mans Master
Joined: Jun 1999
Posts: 6,272
Likes: 2
From: Chino Valley AZ
Cruise-In I Veteran
Cruise-In II Veteran
Currently Corvette-less
Re: A/C compressor won't cycle (PTz-92-LT1)
PT,
When you converted to R-134a, did you disconnect the battery? I know for a fact that the 1992 (most likely others with the C68 Programmer) must be reset to erase stored codes and allow sequencing. You most likely have a low pressure code that is keeping the system de-activated.
Try disconnecting your battery for about 5 minutes, then connect and try again. Also, you must put a static charge on the system before starting the compressor. In my case, I backfilled the system with the R-134a until the system was equalized with the supply pressure. I left the valve open and started the engine, then engaged the compressor. The system took right off.
For what it is worth. I have completely rebuilt my A/C, and the information below highlights a major find.
Cleaning the A/C Evaporator Coils:
Here's how I did it on my 1992 LT1 Coupe:
1. Jack up the front of the car and removed the right front wheel
2. Remove the rear half of the fender well liner
3. Drain and remove the windshield washer reservoir, making sure to unplug the sensor
4. Unplug and remove the blower relay
5. Remove the cross brace that runs between the frame and firewall
6. Remove the blower assembly
7. Remove the heater hoses from the heater core, be prepared to lose a little coolant
8. Remove all the screws that attach the passenger side of the blower housing to the firewall
9. Remove the screws that hold the passenger half of the housing to the driver side half
10. Carefully split the housing at the evaporator split line, leave the monkey poopie in place
11. The air flow inlet side of the evaporator will be facing the passenger side
12. If it is like mine, it will be caked with an oily/tar dirt
13. Gently remove as much of the bulk as possible
14. Line the bottom of the evaporator coil with rags
15. Spray disk brake cleaner into the evaporator coils to remove the oil and grease
16. Try to have access to an air compressor so that you can vaporize as much cleaner as possible
17. The air flow outlet side of the evaporator will not be dirty. Don’t mess with it
18. Reverse the steps to re-assemble
Re-use the monkey poopie to seal the air around the evaporator inlet and outlet lines
When you converted to R-134a, did you disconnect the battery? I know for a fact that the 1992 (most likely others with the C68 Programmer) must be reset to erase stored codes and allow sequencing. You most likely have a low pressure code that is keeping the system de-activated.
Try disconnecting your battery for about 5 minutes, then connect and try again. Also, you must put a static charge on the system before starting the compressor. In my case, I backfilled the system with the R-134a until the system was equalized with the supply pressure. I left the valve open and started the engine, then engaged the compressor. The system took right off.
For what it is worth. I have completely rebuilt my A/C, and the information below highlights a major find.
Cleaning the A/C Evaporator Coils:
Here's how I did it on my 1992 LT1 Coupe:
1. Jack up the front of the car and removed the right front wheel
2. Remove the rear half of the fender well liner
3. Drain and remove the windshield washer reservoir, making sure to unplug the sensor
4. Unplug and remove the blower relay
5. Remove the cross brace that runs between the frame and firewall
6. Remove the blower assembly
7. Remove the heater hoses from the heater core, be prepared to lose a little coolant
8. Remove all the screws that attach the passenger side of the blower housing to the firewall
9. Remove the screws that hold the passenger half of the housing to the driver side half
10. Carefully split the housing at the evaporator split line, leave the monkey poopie in place
11. The air flow inlet side of the evaporator will be facing the passenger side
12. If it is like mine, it will be caked with an oily/tar dirt
13. Gently remove as much of the bulk as possible
14. Line the bottom of the evaporator coil with rags
15. Spray disk brake cleaner into the evaporator coils to remove the oil and grease
16. Try to have access to an air compressor so that you can vaporize as much cleaner as possible
17. The air flow outlet side of the evaporator will not be dirty. Don’t mess with it
18. Reverse the steps to re-assemble
Re-use the monkey poopie to seal the air around the evaporator inlet and outlet lines
Advanced
Joined: May 2002
Posts: 53
Likes: 1
From: Los Altos CA
Re: A/C compressor won't cycle (PTz-92-LT1)
Several things to check:
1. Confirm that your compressor is receiving the signal to turn on by removing the electrical connector and checking with a voltmeter to see if it's getting power. If not, then you'll have to work backwards from there. It could be the pressure switches, the A/C relay, the A/C controller, or the wiring between all of those. If the compressor is receiving power and not working, then that's the problem part and will probably need to be rebuilt or replaced. Although I see that you have a new compressor.
2. If the compressor is not receiving power, check the status of the low pressure switch with your multimeter set to check resistance. If it's an open circuit, e.g., very high resistance, then it's either bad and can be replaced easily or it's really indicating low pressure. You'll have to use gauges to check the pressure on the low pressure side with the A/C off and running to know for sure. If the low pressure switch is closed (< 2 ohms) , then your A/C controller should be receiving the correct signal to turn on the compressor. At that stage, you'll have to check the A/C power relay to see if it's getting the signal to turn on or not. Get out the wiring diagrams and check out the other components if the relay checks out.
Usually it's either the low pressure switch, insufficient refrigerant or compressor that goes out in A/C systems that have been in operation 10+ years. Best of luck to you. BTW, if it is low on refrigerant, it makes sense to have an A/C technician reclaim the R-134a, pull a vacuum on the system to see if it's okay. You may have a leak that needs fixing.
[Modified by nel, 7:17 PM 6/12/2002]
1. Confirm that your compressor is receiving the signal to turn on by removing the electrical connector and checking with a voltmeter to see if it's getting power. If not, then you'll have to work backwards from there. It could be the pressure switches, the A/C relay, the A/C controller, or the wiring between all of those. If the compressor is receiving power and not working, then that's the problem part and will probably need to be rebuilt or replaced. Although I see that you have a new compressor.
2. If the compressor is not receiving power, check the status of the low pressure switch with your multimeter set to check resistance. If it's an open circuit, e.g., very high resistance, then it's either bad and can be replaced easily or it's really indicating low pressure. You'll have to use gauges to check the pressure on the low pressure side with the A/C off and running to know for sure. If the low pressure switch is closed (< 2 ohms) , then your A/C controller should be receiving the correct signal to turn on the compressor. At that stage, you'll have to check the A/C power relay to see if it's getting the signal to turn on or not. Get out the wiring diagrams and check out the other components if the relay checks out.
Usually it's either the low pressure switch, insufficient refrigerant or compressor that goes out in A/C systems that have been in operation 10+ years. Best of luck to you. BTW, if it is low on refrigerant, it makes sense to have an A/C technician reclaim the R-134a, pull a vacuum on the system to see if it's okay. You may have a leak that needs fixing.
[Modified by nel, 7:17 PM 6/12/2002]
Thread Starter
Racer
Joined: Apr 2002
Posts: 389
Likes: 0
From: Micco FL
Re: A/C compressor won't cycle (nel)
Thanks for the imput...I will dig into the system and post what I find, probably some time tomorrow.
By the way where is the A/C power relay?
[Modified by PTz-92-LT1, 2:39 PM 6/12/2002]
By the way where is the A/C power relay?
[Modified by PTz-92-LT1, 2:39 PM 6/12/2002]
Advanced
Joined: May 2002
Posts: 53
Likes: 1
From: Los Altos CA
Re: A/C compressor won't cycle (PTz-92-LT1)
Sorry, I didn't have my electrical service diagnostic manual handy when I replied to you this a.m.
According to the manual for my 1987 C68 system, the compressor receives power directly and at all times when the engine is running through a 25 amp fuse for the A/C. That's the black/white wire at the compressor. You should check the fuse first to make sure it's not blown. Disconnect the A/C compressor clutch electrical connector and ensure that you're getting 12V on black/white wire (with the engine running). If not, your problem is in the white/black wiring or the fuse block.
The other wire at the compressor is a dark green one which goes into the Blower Control Module located in "front of dash, in LH side of evaporator housing". The BCM serves as the A/C power relay by shorting the circuit to ground (probably with some power transistor circuitry). With the engine running and the A/C turned on, you could check the voltage on this line relative to ground. It should read close to zero. NOTE: DON'T CHECK THE RESISTANCE OF THIS LINE RELATIVE TO GROUND. The BCM is a solid state device, not a physical relay. While I doubt that you could damage it by trying to measure resistance (a multi-meter uses a very low DC current), the service manual advises against doing this.
The only other electrical device in this circuit is the compressor clutch diode which spans across the black/white and dark green wires at the compressor clutch connector and is thus wired in parallel with the compressor clutch coil. This diode shunts the current associated with the BCM grounding and opening the circuit. I'm not sure whether the diode is in the connector with the two wires or is part of the compressor clutch circuitry. That really determines how you go about checking it. If you measure the resistance of the compressor clutch coil (connector off), you should be able to tell if that's okay or not. If you get a funny reading, switch positions on your multi-meter leads (e.g., use the red lead on the pin that you had the black lead on earlier and vice versa).
Best of luck.
According to the manual for my 1987 C68 system, the compressor receives power directly and at all times when the engine is running through a 25 amp fuse for the A/C. That's the black/white wire at the compressor. You should check the fuse first to make sure it's not blown. Disconnect the A/C compressor clutch electrical connector and ensure that you're getting 12V on black/white wire (with the engine running). If not, your problem is in the white/black wiring or the fuse block.
The other wire at the compressor is a dark green one which goes into the Blower Control Module located in "front of dash, in LH side of evaporator housing". The BCM serves as the A/C power relay by shorting the circuit to ground (probably with some power transistor circuitry). With the engine running and the A/C turned on, you could check the voltage on this line relative to ground. It should read close to zero. NOTE: DON'T CHECK THE RESISTANCE OF THIS LINE RELATIVE TO GROUND. The BCM is a solid state device, not a physical relay. While I doubt that you could damage it by trying to measure resistance (a multi-meter uses a very low DC current), the service manual advises against doing this.
The only other electrical device in this circuit is the compressor clutch diode which spans across the black/white and dark green wires at the compressor clutch connector and is thus wired in parallel with the compressor clutch coil. This diode shunts the current associated with the BCM grounding and opening the circuit. I'm not sure whether the diode is in the connector with the two wires or is part of the compressor clutch circuitry. That really determines how you go about checking it. If you measure the resistance of the compressor clutch coil (connector off), you should be able to tell if that's okay or not. If you get a funny reading, switch positions on your multi-meter leads (e.g., use the red lead on the pin that you had the black lead on earlier and vice versa).
Best of luck.
Thread Starter
Racer
Joined: Apr 2002
Posts: 389
Likes: 0
From: Micco FL
Re: A/C compressor won't cycle (nel)
In response to the posting by PurpleC4:
1) Yes, the battery was disconnected during the replacement of the A/C parts. Did it again last evening just for grins…no change.
2) The system was vacuumed and charged at a reliable professional shop. They are the ones that pointed me in the direction of either the head, the A/C programmer, or the temperature sensor.
3) The items above numbered 1-18 describe the process of changing the evaporator. This was not necessary during the conversion. However this seem to be very useful information which I will store for future use.
Thanks
In reference to Nel:
1) The compressor is receiving a signal (13.4 v) when the A/C is suppose to be on and none when the A/C is switched off. What it doesn’t do is cycle when it is on.
2) There is no third green wire on the 92 version, just two wires.
3) The low side and the high side of the system read normal.
Thanks for the assistance.
The issue here is that the compressor does go on and off when switched from inside. What it doesn't do is switch off (cycle) when it turned on inside the car regardless of the temperature. The other thing that it does is the every 30 seconds the heat comes on.
Any other suggestions from anyone?
1) Yes, the battery was disconnected during the replacement of the A/C parts. Did it again last evening just for grins…no change.
2) The system was vacuumed and charged at a reliable professional shop. They are the ones that pointed me in the direction of either the head, the A/C programmer, or the temperature sensor.
3) The items above numbered 1-18 describe the process of changing the evaporator. This was not necessary during the conversion. However this seem to be very useful information which I will store for future use.
Thanks
In reference to Nel:
1) The compressor is receiving a signal (13.4 v) when the A/C is suppose to be on and none when the A/C is switched off. What it doesn’t do is cycle when it is on.
2) There is no third green wire on the 92 version, just two wires.
3) The low side and the high side of the system read normal.
Thanks for the assistance.
The issue here is that the compressor does go on and off when switched from inside. What it doesn't do is switch off (cycle) when it turned on inside the car regardless of the temperature. The other thing that it does is the every 30 seconds the heat comes on.
Any other suggestions from anyone?
Advanced
Joined: May 2002
Posts: 53
Likes: 1
From: Los Altos CA
Re: A/C compressor won't cycle (PTz-92-LT1)
The compressor doesn't necessarily need to cycle. It only cycles if the low pressure or high pressure switches go off which requires the right combination of temperatures. You may be okay on that. As far as the heater coming on every 30 seconds, I'll take a look at my diagnostic manual tonight and see if I can come up with some hypotheses. You may also want to try posting on the aircondition.com website. They have some real A/C experts that have probably seen this problem before.
Thread Starter
Racer
Joined: Apr 2002
Posts: 389
Likes: 0
From: Micco FL
Re: A/C compressor won't cycle (nel)
Good advise on the "aircondition.com website" I'll give that a try.
In the meantime here is as update. Replaced the A/C Programmer yesterday...same problem. So no to date the compressor, evaporator, oriface tube, fan, ECM, and A/C programmer have been changed out, and the original problem still exists. Let me see what is left, the A/C head, sun load sensor, interior sensor, blower module and CCM.
Visited yet another GM dealership yesterday afternoon and have an appointment for Tuesday morning. This will be the 4th shop visited. Wonder what will be their suggestion and bill?
Will keep you posted.
In the meantime here is as update. Replaced the A/C Programmer yesterday...same problem. So no to date the compressor, evaporator, oriface tube, fan, ECM, and A/C programmer have been changed out, and the original problem still exists. Let me see what is left, the A/C head, sun load sensor, interior sensor, blower module and CCM.
Visited yet another GM dealership yesterday afternoon and have an appointment for Tuesday morning. This will be the 4th shop visited. Wonder what will be their suggestion and bill?
Will keep you posted.
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Advanced
Joined: May 2002
Posts: 53
Likes: 1
From: Los Altos CA
Re: A/C compressor won't cycle (PTz-92-LT1)
Sorry it took so long for me to reply. The problem is probably in the chain of components associated with the temperature controls. These components include: inside temp. sensor, outside temp. sensor, the Heater & A/C Control Assembly (that's the one at the dash with displays and buttons), the Heater & A/C Programmer, and the Air Mix Valve Actuator.
Air from the blower motors always flow through the evaporator. The temperature valve, which is mechanically tied to the Air Mix Valve Actuator, determines whether air flows through the heater core. So it sounds like you've got some sort of weird cycling going on that is moving the temperature valve around.
Have you tried putting the system into diagnostic mode? You do this by holding down the rear defrost button, then press and release the Blower Manual Up button. According to my electrical diagnostic manual, a number preceded by a minus sign will be displayed, showing what mode you are in. You advance the modes by pressing the Warmer button. And, you can display the contents of each mode by pressing the Cooler button.
Mode 1=Program Number
Mode 2=In-car thermistor
Mode 3=Ambient correction
Mode 4=Blower number
Mode 5=Outside temperature thermistor
Mode 6=Feedback pot position (there's a position pot at the air mix valve)
Mode 7=Calculated door position
Mode 8=system faults
Mode 9=Software version number
You want to go into Mode 8 and display any error codes. It looks like Error 1 is associated with the feedback pot in the air mix valve actuator. Error 2 and 4: outside sensor. Error 8 and 16: in-car sensor.
Good luck in chasing this down. It could be the air-mix valve actuator located behind the right hand side of the IP on the heater & A/C plenum. Or, it could be something simple like a bad connection on one of the sensors.
Air from the blower motors always flow through the evaporator. The temperature valve, which is mechanically tied to the Air Mix Valve Actuator, determines whether air flows through the heater core. So it sounds like you've got some sort of weird cycling going on that is moving the temperature valve around.
Have you tried putting the system into diagnostic mode? You do this by holding down the rear defrost button, then press and release the Blower Manual Up button. According to my electrical diagnostic manual, a number preceded by a minus sign will be displayed, showing what mode you are in. You advance the modes by pressing the Warmer button. And, you can display the contents of each mode by pressing the Cooler button.
Mode 1=Program Number
Mode 2=In-car thermistor
Mode 3=Ambient correction
Mode 4=Blower number
Mode 5=Outside temperature thermistor
Mode 6=Feedback pot position (there's a position pot at the air mix valve)
Mode 7=Calculated door position
Mode 8=system faults
Mode 9=Software version number
You want to go into Mode 8 and display any error codes. It looks like Error 1 is associated with the feedback pot in the air mix valve actuator. Error 2 and 4: outside sensor. Error 8 and 16: in-car sensor.
Good luck in chasing this down. It could be the air-mix valve actuator located behind the right hand side of the IP on the heater & A/C plenum. Or, it could be something simple like a bad connection on one of the sensors.
