1995 Cutlass Ciera AC

[mptc]

Question regarding air conditioning. Is the AC Refrigerant Pressure Sensor the same thing as the AC Refrigerant Pressure Transducer? Do they perform the same function? My Cutlass Ciera does not have a high and low cut-off switch. Is there a source for GM Part number for this piece?

Thank you in advance.

mptc

[brcidd]

Yes, they are the same. You have a pressure transducer (three wires on high side line) and you indeed have a high and a low cut-off- the car's computer decides that. You have a variable stroke compressor that does not use a cycling switch because it does not cycle by design.

The number one cause of compressor not coming on is loss of refrigerant due to a leak- your V-5 compressor will run with only 5 ounces refrigerant in it- factory spec is nearly 32 ounces or so (on underhood label)

4 cylinder or 6 cylinder engine? they may be different a/c systems.

[Tech II]

On the old pressure cycling switch of the old CCOT system, you could jumper out the switch to see if that was the problem.....you can't do that with the pressure switch.......

Have you checked hi/lo pressures with car off? should be close to ambient temp, for example, if it is 70 F outside on a cold engine, hi/lo = 70 psi......if much lower, you have a leak.....

Do you have access to a scan tool? Does it read the same a/c pressure as the gauges?

[mptc]

It has a 3.1L V-6.

[mptc]

Originally Posted by Tech II

On the old pressure cycling switch of the old CCOT system, you could jumper out the switch to see if that was the problem.....you can't do that with the pressure switch.......

Have you checked hi/lo pressures with car off? should be close to ambient temp, for example, if it is 70 F outside on a cold engine, hi/lo = 70 psi......if much lower, you have a leak.....

Do you have access to a scan tool? Does it read the same a/c pressure as the gauges?

I do not have a scan tool...at least not an OBD1. What I did do is with the ignition on and the engine off and the pressure sensor disconnected and the ac selector to the "max" position with a digital volt meter I jumpered reference (gray) wire and the signal (red/black) wire and it measured 4.84 volts which is below the 4.92 (high end) volts. Using DVM I connected the reference (gray) wire to ground. It measured near 5 volts (4.98). I also connected the reference (gray) wire and the ground (black) wire and it measured 5 volts (which is reference voltage). So I know the ground wire is good. In addition I did replace the signal wire (red/black).

The sensor is a new replacement. I have tried 2 different PCMs (used) with the same results. I believe the wiring and connections are all good. Now the sensor may be a lemon. Or it could be that the code (1530) is present and until it is cleared it won't operate the compressor. Beyond that I am at a loss of what is next.

[Tech II]

have you checked pressure in the system with gauges?

[brcidd]

It takes at minimum 47 psi for compressor to be enabled- have you measured signal voltage with transducer plugged in. It should be somewhere near 1 volt as I recall at ambient of 70 deg and compressor off.

Put some gauges on it- you may have an empty system and the transducer and computer aredoing waht they are suposed to- keep the compressor off.

[mptc]

Originally Posted by Tech II

have you checked pressure in the system with gauges?

Not lately. The system has been checked, drained and recharged previously (last fall) when I was still having trouble with it. It held the pressure, no leaks or any indication of leaks. I quit working on it through the winter.

[mptc]

Originally Posted by brcidd

It takes at minimum 47 psi for compressor to be enabled- have you measured signal voltage with transducer plugged in. It should be somewhere near 1 volt as I recall at ambient of 70 deg and compressor off.

Put some gauges on it- you may have an empty system and the transducer and computer aredoing waht they are suposed to- keep the compressor off.

I have no way of measuring the signal voltage with the transducer plugged in. No scan tool.

[Tech II]

You can back probe the signal wire while it is plugged in to read the signal with the key on.......Just because it was charged last year, does not mean it is charged this year.....these compressors are famous for leaking at the front seal, and also at the service valves....

One more thing.....the place you should really back probe the signal line, is at the ECM....this will tell you the integrity of the line, and if the ECM is receiving the signal....

[mptc]

Originally Posted by Tech II

You can back probe the signal wire while it is plugged in to read the signal with the key on.......Just because it was charged last year, does not mean it is charged this year.....these compressors are famous for leaking at the front seal, and also at the service valves....

One more thing.....the place you should really back probe the signal line, is at the ECM....this will tell you the integrity of the line, and if the ECM is receiving the signal....

I will try that this weekend and report back. Should I be looking at 1 volt? Is the 70 degrees ambient temp the outside temp? If it is we won't be there for another month or so.

[mptc]

Originally Posted by Tech II

You can back probe the signal wire while it is plugged in to read the signal with the key on.......Just because it was charged last year, does not mean it is charged this year.....these compressors are famous for leaking at the front seal, and also at the service valves....

One more thing.....the place you should really back probe the signal line, is at the ECM....this will tell you the integrity of the line, and if the ECM is receiving the signal....

Okay...back probed signal wire at ECM. The specs call for voltage of 0.1 volts at 0 psi up to 4.9 volts at 450 psi or more. The best I could get was 0.01 to 0.03 volts with DVM set at 20. So basically no voltage. I did this with the key on, engine off and the AC switch at max. I also did it with the key on, engine on and the AC switch set at max. (Note the ambient (outside) temp is 50 degrees).

[Tech II]

That voltage means you have no refrigerant in your system....no wonder it won't run...this will be verified with gauges attached.....

[mptc]

Originally Posted by Tech II

That voltage means you have no refrigerant in your system....no wonder it won't run...this will be verified with gauges attached.....

Okay...here is the update.

1) I had the refrigerant drained (it only had 5 oz. in it). However it held the vacuum for several minutes (indicating no leak in the system).

2) I replaced the a/c pressure sensor (the one I bought previously off of eBay was evidently not compatible with the 95 Ciera 3.1L). In addition, the O-ring had a chunk missing. So that was replaced when putting in the new a/c pressure sensor.

3) The new sensor did not work. I was getting the same .02 or .03 voltage on the signal wire at the PCM (with key on, engine not running and a/c selector switch on).

4) I disconnected the pressure sensor connector and jumpered the reference line (5 V) with the signal wire (according to diagnostic flow chart) it was reading 4.97 volts on the signal wire at the PCM and the secondary cooling fan kicked on (which it should) indicating that the wiring was good.

5) So the system was drained once again. I put the "original" a/c pressure sensor back in (not the one from eBay but previous to that). Now I am getting voltage of 1.10 on the signal wire at the PCM (with the key on and the a/c selector switch turned on). But no secondary fan, no compressor nothing.

So the a/c pressure sensor is operating. The wiring from the a/c pressure sensor to the PCM is good. I can jumper the compressor and it will kick on. The system is charged and holds a vacuum (no leaks).

What am I missing? I have been at this on and off for 2 years.

HELP!

mptc

[mptc]

I have a scan tool read codes and none were present (looking for 1530). I had them cleared anyway. When monitoring the A/C the pressure read 101.7 and the tool showed that the A/C was being requested but the compressor was not running and no cool air. This in addition to the information in the previous post has me at a complete loss as to where to look next.

Any help would be greatly appreciated!

mptc