Strange Air Conditioning Issue
06-12-2012, 05:29 PM
#1
Drifting
Thread Starter
Strange Air Conditioning Issue
I am working on the R12 A/C System on a 1987 Corvette with an Automatic. I am doing my best to try and get this done right, but the tools to do it right are harder and harder to come by.
This is what I have done so far; System was empty when I received the vehicle. I pulled a vacuum on the system for an hour. To do this I went out and purchased R134A Conversion ports and connected. This way I was able to hookup my 134A Manifold Gauge Set. I have about 6 cans of R12 Left so I want to make sure they don't get used in vein. General Motors states that if the system holds vacuum for 5 minutes its good to go. After 5 minutes I noticed the pressure in the system start to bleed off so I decided to replace all the o-rings with updated green ones, put in a new accumulator, and a new orifice tube. I added 4oz of Mineral oil to the accumulator, 1oz to the compressor, and 1oz to the area of the orifice tube. I pulled Vacuum again. It held at 29 for more then 5 minutes. On most systems I do I will let the gauge set sit on the system overnight. That is the ultimate leakage test. Unfortunately after 1 hour vacuum slowly started to bleed off. However I know R12 is heavy/thick so I decided to take my chances and add 3 cans of R12 which is the recommended amount. I have a 30 year old can hose I used. The refrigerant took about 20 minutes a can with the compressor cycling non stop before I finally made it through all 3 cans and the compressor stayed on and the accumulator and larger line stayed cold. Throughout the induction of the R12 I noticed my line was leaking a little for time to time. Its old. But I am pretty sure 95% of the refrigerant made it into the system. What happened next baffles me. I turned the car off, it cooled down. I restarted it and turned the A/C on. The A/C blows ICE Cold till the car gets to about 190*F then they compressor begins cycling and the system only blows hot air! I couldn't figure out what was wrong. For whatever reason I decided to pull the plug out of the switch on the orifice tube line (I believe it is called the Compressor High Pressure Switch). The one closer to the bend. Upon doing so the fans kicked on along with the compressor and the system seems to be functioning properly.
Today I put the fittings back on the system in an attempt to diagnose the problem. With the Compressor High Pressure Switch connected, this is what i found:
The Static Pressure with the vehicle off and cold at 69*F Outside:
Low Side (Blue) 75
High Side (Red) 75
Dynamic Pressure with the vehicle running initially
Low Side 40
High Side 205
Dynamic Pressure with the vehicle running in closed loop
Low side 60
High Side 450
*NOTE: The pressure switch cuts the compressor off when the pressure exceeds 450PSI on the high side.
Static Pressure HOT
Low Side 120
High Side 120
_______________________________________
I decided to do readings after again disconnecting the switch was disconnected with the engine at operating temperature. To make this easier I took a video. This is what I found; The system was functioning properly.... except the fans were constantly. As a test to see if I put too much refrigerant & oil in the system I let some out. AC is not blowing AS cold as before but i can refill it a little once I fix the problem.
This is what I have done so far; System was empty when I received the vehicle. I pulled a vacuum on the system for an hour. To do this I went out and purchased R134A Conversion ports and connected. This way I was able to hookup my 134A Manifold Gauge Set. I have about 6 cans of R12 Left so I want to make sure they don't get used in vein. General Motors states that if the system holds vacuum for 5 minutes its good to go. After 5 minutes I noticed the pressure in the system start to bleed off so I decided to replace all the o-rings with updated green ones, put in a new accumulator, and a new orifice tube. I added 4oz of Mineral oil to the accumulator, 1oz to the compressor, and 1oz to the area of the orifice tube. I pulled Vacuum again. It held at 29 for more then 5 minutes. On most systems I do I will let the gauge set sit on the system overnight. That is the ultimate leakage test. Unfortunately after 1 hour vacuum slowly started to bleed off. However I know R12 is heavy/thick so I decided to take my chances and add 3 cans of R12 which is the recommended amount. I have a 30 year old can hose I used. The refrigerant took about 20 minutes a can with the compressor cycling non stop before I finally made it through all 3 cans and the compressor stayed on and the accumulator and larger line stayed cold. Throughout the induction of the R12 I noticed my line was leaking a little for time to time. Its old. But I am pretty sure 95% of the refrigerant made it into the system. What happened next baffles me. I turned the car off, it cooled down. I restarted it and turned the A/C on. The A/C blows ICE Cold till the car gets to about 190*F then they compressor begins cycling and the system only blows hot air! I couldn't figure out what was wrong. For whatever reason I decided to pull the plug out of the switch on the orifice tube line (I believe it is called the Compressor High Pressure Switch). The one closer to the bend. Upon doing so the fans kicked on along with the compressor and the system seems to be functioning properly.
Today I put the fittings back on the system in an attempt to diagnose the problem. With the Compressor High Pressure Switch connected, this is what i found:
The Static Pressure with the vehicle off and cold at 69*F Outside:
Low Side (Blue) 75
High Side (Red) 75
Dynamic Pressure with the vehicle running initially
Low Side 40
High Side 205
Dynamic Pressure with the vehicle running in closed loop
Low side 60
High Side 450
*NOTE: The pressure switch cuts the compressor off when the pressure exceeds 450PSI on the high side.
Static Pressure HOT
Low Side 120
High Side 120
_______________________________________
I decided to do readings after again disconnecting the switch was disconnected with the engine at operating temperature. To make this easier I took a video. This is what I found; The system was functioning properly.... except the fans were constantly. As a test to see if I put too much refrigerant & oil in the system I let some out. AC is not blowing AS cold as before but i can refill it a little once I fix the problem.
Last edited by Danspeed1; 06-12-2012 at 05:44 PM.
06-12-2012, 07:03 PM
#2
Melting Slicks
Member Since: Aug 1999
Location: Baltimore, MD USA
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You've already diagnosed the problem.
The AC coolant fan switch is bad, the one you
installed from the 89 is also bad or the schrader valve
the AC fan switch screws on to is bad.
The fan switch should open when the pressure reaches
around 233 psi.
The ECM then turns on the radiator fan.
You proved by disconnecting the AC fan switch
connector the ECM can turn on the radiator fan. That
eliminates the ECM and the wiring from the
ECM to the AC coolant fan switch.
Read this thread.
The schematics shown are for a 89 but the 87 should be similar.
http://forums.corvetteforum.com/c4-t...g-with-ac.html
The AC coolant fan switch is bad, the one you
installed from the 89 is also bad or the schrader valve
the AC fan switch screws on to is bad.
The fan switch should open when the pressure reaches
around 233 psi.
The ECM then turns on the radiator fan.
You proved by disconnecting the AC fan switch
connector the ECM can turn on the radiator fan. That
eliminates the ECM and the wiring from the
ECM to the AC coolant fan switch.
Read this thread.
The schematics shown are for a 89 but the 87 should be similar.
http://forums.corvetteforum.com/c4-t...g-with-ac.html
Last edited by Hooked on Vettes; 06-12-2012 at 07:11 PM.
06-12-2012, 07:43 PM
#3
yep...
the a/c fan relay may be worth looking at, certainly the pressure switch. The system is fairly simple in its operation..
next time it cuts out when hot or warmed up and starts blowing hot air...hose down the condensor or set a fan in the nose to blow air on the HOT condensor and it will suddenly start cooling again.
Pressure switch tells the ECM its time for fan(s) to come on whenever there is a rise in system pressure indicating the system is running, then the fan relay gets permission to energize the fan. Air flows across the condensor dropping the head pressure to below the cut-out limit.
06-12-2012, 08:09 PM
#4
Drifting
Thread Starter
yep...
the a/c fan relay may be worth looking at, certainly the pressure switch. The system is fairly simple in its operation..
next time it cuts out when hot or warmed up and starts blowing hot air...hose down the condensor or set a fan in the nose to blow air on the HOT condensor and it will suddenly start cooling again.
Pressure switch tells the ECM its time for fan(s) to come on whenever there is a rise in system pressure indicating the system is running, then the fan relay gets permission to energize the fan. Air flows across the condensor dropping the head pressure to below the cut-out limit.
I couldn't find that information anywhere! I was wondering for the last two days what about the function of that switch could cause the concern I was seeing.
DG
06-13-2012, 09:09 AM
#6
Le Mans Master
............. The green o-rings might bite you in the a** in time ... they are not compatible with the oil used in R12 systems ... and vice versa ... hence the change ...............
06-13-2012, 09:21 AM
#7
Melting Slicks
I just recently purchased a set of "Green" seals for an R12 system that were rated for both R12 and R134. It will indicate on the Oring package what the Compatibilities are. The same for "Black" seals....read the package!