Air Conditioning problem
1998 Cadillac El Dorado V8 Front Wheel Drive Automatic 101000 miles

System stopped working, compressor will not come on. Dashboard signals "check A/C system" and "low refigerant pressure, A/C off" alternately. Mechanic evacuated and recharged the system with no change. He then jumped out the A/C relay in the fuse box under the hood and the compressor came on. System then worked flawlessly and was 45 degrees at the interior vents. Everything works fine with the jumper wire. Prior to recharge the inline filter (plastic) was replaced (there was no debris on it). New A/C relay did not correct the problem. I bought a climate control assembly for the dashboard and replaced the blower motor on the firewall, I even bought a new computer and nothing will make the compressor come on, but obviously the sytem is able to work fine. Tried to jump out the two sensors on the high side pipe that runs accross the firewall L to R. Nothing will make the compressor come on (other than jumping out the relay) or the allerts go away on the dash. Disconnected the battery at every repair attempt. The heater, the defroster (without the compressor coming on) and the blower all work fine. When you press the A/C button on the climate control, the system comes on but blows warm air. One of the mechanics I spoke to said the 'fan controller module' is bad but I don't know where that is or if it could be the culprit. My mecaninc (and I) have given up. HELP

Is it still saying "a/c low" or any other a/c warning on the driver info center? Caddy's wont let the compressor come on til the codes have been cleared through the on-board system.To enter self diagnostics

Key on, press "warmer" and "off" at the same time,hold down until info center changes to diagnostic. Then press fan low until "ACM" is displayed.Then fan high until "ACM codes" is displayed.Then fan low until "clear ACM codes" is displayed. Then fan high to clear the codes "ACM codes cleared " will display. Turn key off.

I followed your instructions to clear the ACM codes but the compressor will still not come on. I am still getting the messages "low refrigerant A/C off" and "Service A/C system". What now?

Then the problem isnt fixed.......... sounds like the pressure sensor (located in the high side line) is bad if the system is full. If there are any error codes, the car wont let the comp turn on

2CarPro Jack wrote:

Then the problem isnt fixed.......... sounds like the pressure sensor (located in the high side line) is bad if the system is full. If there are any error codes, the car wont let the comp turn on

There are two sensors on the high side (small tubing) and one big one on the low side (one inch + diameter tubing). Which one of the two would it be? one is near the dryer and one is on the drivers side. Can I replace it without loosing the freon and/or can I jump it out to see if it is bad (I think I may have done that already??) If I understand you correctly, even after I find a problem and fix it I will have to reset all the error codes on the dash. Can I reset them all or just the ACM? I know this is a pain but I have been at this for weeks and as you can see at considerable expense.

My software doesnt say which is which... what color are the wires to the two switch's and I will try looking them up in the wiring diagram

The low side (large tube) sensor has a pink and a green wire. The high side sensors are black and grey on the passengers side of the tube and dark blue and black on the drivers side. Let me know which one and if I can jump it out before I replace it. Also can I replace it without loosing the Freon?
Thanks,

Im showing a dark blue/dark green for the high side pressure switch.I wouldnt jump it. According to Mitchell you dont have to discharge the system, but honestly I would just to be safe

I bought the new high pressure sensor from Cadillac but we still have problem. There are two sensors on the high pressure line that runs along the firewall from right to left. Parts dept at Cadillac says there is only one according to their diagram. I don't want to replace the wrong one (assuming that this is indeed the problem) and loose the Freon multiple times. The high pressure line starts at the passengers (right) side of the firewall and travels across to the drivers (left) side of the car and then turns down below the master cylinder and then turns forward toward the condensor and attaches to it. That line looks like 1/2 inch diameter (guess) aluminum tubing. The line coming out of the evaporator (enclosed in the fan box assy) is 3/4 inch diameter (guessing) and gets reduced to 1/2 inch at the coupling that joins it to the high pressure line. There is a sensor on that 3/4 inch line (right before the coupling) that has a black and a grey wire attached to it and when I jump out the relay to engage the compressor that line gets ice cold. It changes to extremely hot right at the coupling point where it is ruduced to the 1/2 iinch line. That 1/2 line gets untouchably hot all the way across the firewall. The second sensor with the blue and black (looks black to me and not green) is located on that 1/2 in line all the way over on the drivers side of the firewall. Which one do I replace? Is the proceedure after replacement to clear the codes on the diagnostic (all of them or just the ACM?) and then recharge the system, or the other way around. Thanks for your patience
Bob Smith

Try using a voltmeter on the switch plugs when comp is running, one is s switch and the other is a senor so the switch will simply turn on and off with 12 volts while th eother will send a signal that is of varying voltage