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compressor does not engage

kevinn on Fri August 08, 2008 9:45 PM User is offline

Year: 1995
Make: Buick
Model: Century
Engine Size: 3.1
Refrigerant Type: 134a
Ambient Temp: 80f
Pressure Low: 85
Pressure High: 85
Country of Origin: United States

The compressor will not engage. When the gauge was first connected, readings were 15/15. Added 134a and now its up to 85/85 but the compressor will not engage. There is no power going to the compressor with A/C on max and fan on high. Cannot seem to locate any low-pressure switches in the system, only one on the high side (which has 3 wires- red, white and black). What I believe to be the compressor fuse, a 20a tucked behind the glove box, is good.

What else should I check?

johnboy123 on Fri August 08, 2008 10:46 PM User is offlineView users profile

Hi..was it working earlier?...making any noise...belt smoking? Had you done any work to the reed valves or replaced the orifice tube or anything else to the compressor? Can you turn the compressor clutch (engine off) by hand?

kevinn on Sat August 09, 2008 12:41 AM User is offline

It worked last fall, but have been going without A/C this summer as it did not work the first time I tried to use it this year. Haven't done anything to the system except charge it. Compressor turns smoothly with the engine off.

Chick on Sat August 09, 2008 5:46 AM User is offlineView users profile

Your system has a three wire pressure transducer, and cannot be jumped. Your system was empty, (15psi on an 80degree day) so a evacuation and recharge into a good vacuum should allow the compressor to start. Make sure no codes are present to prevent the compressor from starting, a battery disconnect will clear them, common leak point on that system is the compressor front shaft seal..Hope this helps..

You can add some UV dye to aid in leak detection, but don't add sealers of other magic in a can...

Email: Chick


Freedoms just another word for nothing left to lose

kevinn on Sat August 09, 2008 12:31 PM User is offline

Disconnected the battery for a few minutes to no avail. Is a vacuum really necessary to get the compressor to engage? I hate to spend even more money on a tool I will use only once.

iceman2555 on Sat August 09, 2008 1:33 PM User is offlineView users profile

This compressor installed on this vehicle is a V5 series. It has not LPCO switch.
If the electrical connection indicates no voltage....obtain a wiring diagram for the vehicle and start a trace to find the problem. As Chick states...DO NOT try jumping the three wire connector...serious damage may is quite possible this has already occurred....and the reason for the non engagement of the clutch.
To determine if the clutch does engage.
With the ENGINE OFF....remove the connector to the clutch coil (wiring harness) and using a jumper....source a known 12volt supply and attempt to engage the clutch.
It is essential that the system be evacuated (vacuum) prior to recharging and compressor operation.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

kevinn on Sun August 10, 2008 7:49 PM User is offline

With the A/C on there is 0.07v at the relay, 0v with A/C off. Is that normal or should I see 12v?
All 3 wires from the pressure switch run back to the ECM. Is it safe to test voltage on these with multimeter? Thought I read on another post here that putting a multimeter between them and ground can damage the ECM.

Forgot to mention earlier, the auxiliary cooling fan does not turn on either.

befuddled on Sun August 10, 2008 11:35 PM User is offline

You can borrow the vacuum pump and guages from Autozone.

GM Tech on Mon August 11, 2008 9:19 AM User is offline

Are you sure the pressure went into the system and not just your gage on low side? -- that compressor should start up right at 47 psi transducer seeking pressure--- also the fans don't come on until 175 psi high side transducer seeking pressure-- so compressor has to be running to do that.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Edited: Mon August 11, 2008 at 9:21 AM by GM Tech

kevinn on Mon August 11, 2008 5:36 PM User is offline

Connected the compressor to a 12v source and the A/C works. Don't remember the exact readings, but they were around 35/200, even still there was no power being provided to the compressor nor did the fan kick on. Is it possible to test the switch with a multimeter?

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