AC compressor waits a few minutes before turning on

[brmurph]

1998 Deville (concours), just had the oil manifold/pan gasket replaced, new front stabalizer bar (old one bar broke if you can believe that) and AC charged. I am very happy with the repair and all was working great for the first week or two but now all of a sudden the AC compressor doesn't turn on until after the car has been running for a few minutes, once it starts running it continues to work fine until the next time the car is started. Once the compressor starts the AC is about as cold as it has ever been (gets down to 47 degrees or so, before the repair 50 was about as good as I could get). There are no HVAC related codes current or history.

Any thoughts? Thanks in advance.

Brian

[rockfangd]

Hmm. That is kind of a new one.

I would find out if the clutch itself is not engaging or if it is but not blowing cold.

If I had to say I would think that the tolerance got changed for the clutch on the compressor.\

after it has engaged does it work normally if cycled off then back on?

[Cadillac Jim]

You can also tell by raising the hood and starting the car, then standing over the compressor. The clutch will give an audible click when engaging and less of a click when disengaging, and you can see whether it is turning or not.

The 1997 FSM, page 1B-6, has this interesting paragraph:

An anti-slugging feature is incorporated which will remove liquid refrigerant that may collect at the compressor. This operation will normally occur once a day after prolonged (overnight) soak for several hours. On initial crank, the heater and A/C programmer will check for indications of this condition and, if found, the A/C clutch will engage. After the engine is started or shortly thereafter, the clutch will disengage and wait until the normal calibrations and parameters are met to signal engagement of the clutch.

If this is what is happening, it is normal and the PCM and A/C programmer are protecting the compressor from hard starting when some liquid Freon is in the compressor. I think that the condition may be sensed by a pulse at the high pressure switch, and is more likely when the system has too much Freon.

The next thing I would look at is the A/C relay, which on the 1997 models is one of the two relays (the other being the fuel pump relay) on top of the under-hood fuse/relay center and Maxifuse block; these are the only two relays that you can access without opening the cover. The main other things mentioned in the FSM are the low refrigerant switch and the high pressure switch, and the wiring harness connections, particulary the DK GRN and DK BLU wires to the high pressure switch and the A/C relay ground, the DK GRN/WHT wire to the PCM (watch out for a static-sensitive PCM connection there!)

Note that there was a platform change for the 1998 Deville and my FSM is for the 1997 model year. The next year that I have an FSM for is 2002, which I have found accurate for some earlier models of Seville and Deville; I'll check that if needed - but there are those here that have 1998 FSMs and experience with that platform.

[brmurph]

Rockfangd yes once it starts it doesn't seem to fail until the car has been off long enough to cool (like the next day).

Jim That anti-slugging feature is also in my manual (oem) but seems to turn the compresser on temporarily, that being said I suppose some where in that part of the circuit could be failing and not allowing it to start (interesting to say the least).

I just went out and started it with the AC on and let it idle for about 15 minutes, the compressor never came on (ambient temperature over 90). I then put it in gear to drive around the block and within 30 seconds of driving the compressor came on and worked just fine. After the test ride I swapped out the FP and compressor relay, guess we shall see tomorrow when I start it if that effected anything. .

Thanks for the help.

[Cadillac Jim]

The process from the FSM text, which is not crystal clear, seems to say that the compressor clutch engages when you turn on the key. When you turn to Start, the clutch disengages and when the engine starts and the key comes back to Run, the compressor engages again - but if there is a pressure spike on the output side of the compressor, it will instantly disengage the compressor clutch. Unless you have the hood up and are watching the compressor, you would never know that the clutch ever engaged.

You might put some gauges on it and see what's up. The system might have air in it, or it might be slightly overfilled.

[rockfangd]

I am thinking exactly the same. It is slightly overfilled and is spiking the high pressure switch on startup, then after a few minutes or so it drops enough to engage the system.