94 Vette - No A/C

[mauijim]

I have a 1994 Vette that until late last Summer had bone chilling cold A/C.
It went from fully functional to no A/C in two days. The radiator cooling fans also run all the time. This unit has electronic temp control - Heat works fine.

1. I checked all fuses - Ok. Although when I removed and replaced the ETC fuse it blew when replaced (w/ ignition off). I disconnected battery, replaced fuse, and no more blown fuses....very strange.

2. I checked R134a charge - Ok

3. The car has 4,400 miles on it and never driven in Winter or Rain....I Know, I Know - it is not a trailier queen. They are performance miles.

4. Also - earlier this Summer while checking voltage to clutch, switches, etc. the A/C engaged and cooled well - no clutch cycling. All good things, but has not worked again since then.

5. One possibility maybe the CC switch, but that doesn't explain why the cooling fans run all the time. Is it possible that a sensor has gone bad or the ETC head has failed?

Please advise - Jim

 

[jim coulter]

I dont know much about a/c units, but maybe c4c5 specialist will come along. anyway this should move this to top.

 

[ecss]

There are probably some PCM error codes set and that is why the fans are on.

Short pin 4 to pin 12.
Turn the ignition to run (don't start the engine).

Any codes will be displayed in the Speedometer LCD area.

1.1 are errros for the CCM
4.1 are errors for the PCM
9.0 are errors for ABS/TSC
A.0 are errors for DERM (Air bag)


Diag. connector above driver side right knee looks like this.

[01|02|03|04|05|06|07|08]
[09|10|11|12|13|14|15|16]

 

[mauijim]

Thanks for the input. One other piece of data. Last evening I continued my investigation. When the high pressure switch is unplugged the cooling fans shut off. Is it possible the HP switch is defective?

 

[larry bud]

I have a 1994 Vette that until late last Summer had bone chilling cold A/C.
It went from fully functional to no A/C in two days. The radiator cooling fans also run all the time. This unit has electronic temp control - Heat works fine.

1. I checked all fuses - Ok. Although when I removed and replaced the ETC fuse it blew when replaced (w/ ignition off). I disconnected battery, replaced fuse, and no more blown fuses....very strange.

2. I checked R134a charge - Ok

3. The car has 4,400 miles on it and never driven in Winter or Rain....I Know, I Know - it is not a trailier queen. They are performance miles.

4. Also - earlier this Summer while checking voltage to clutch, switches, etc. the A/C engaged and cooled well - no clutch cycling. All good things, but has not worked again since then.

5. One possibility maybe the CC switch, but that doesn't explain why the cooling fans run all the time. Is it possible that a sensor has gone bad or the ETC head has failed?

Please advise - Jim

Is the compressor kicking on?

 

[mauijim]

No - Compressor not engaging and cooling fans run continously - I suspect a defective high pressure switch or....another electrical problem.

With system turned on and engine running - no compressor engagement. However, when I unplug high pressure switch fans turn off. Compressor obviously cannot turn on at this point - per design. I don't know if switch is normally open or normally closed under pressure.

I hate to buy a switch ($52.68) and find out it is not the issue!!

 

[ecss]

No - Compressor not engaging and cooling fans run continously - I suspect a defective high pressure switch or....another electrical problem.

If the sensor is defective and is telling the ECM the refrigerant pressure is above 448 psi (4.86 volts at the gray/red wire at the pressure sensor) for over 10 seconds, DTC 66 will set.

The ECM will turn on the cooling fans and will disable the compressor clutch. The ECM will NOT turn on the MIL/ Service Engine Soon lamp.

 

[mauijim]

94 Vette - Now Has A/C!!

If the sensor is defective and is telling the ECM the refrigerant pressure is above 448 psi (4.86 volts at the gray/red wire at the pressure sensor) for over 10 seconds, DTC 66 will set.

The ECM will turn on the cooling fans and will disable the compressor clutch. The ECM will NOT turn on the MIL/ Service Engine Soon lamp.

***********************************************************
Thanks- I did replace the high pressure switch and it resolved the problem.
$58.26 for a pressure switch! A bit pricey.