Service AC System / AC Compressor Off
 

Well Guys, still having an AC problem. I get this message. When I push the Auto/Econ button, the AC comes on and the compressor kicks on. But sure enough whether immediately or after 5-10 seconds, it goes back off. The book says that the message means that a sensor is not functioning. I have changed the low and high pressure switches and the relay. Fans kick on and all. I took it back to Express Oil Change and they checked the freon level. It still reads full at 2.0 lbs (according to the Caddy's Manual). And they say the pressure levels are good for a good cool. I'm stumped, what other sensors/switches could it be? It's starting to cool off in Alabama, so AC is not an emergency at this point. But it does effect how the Defrost and Defog options work. Very humid here.

RE: Service AC System / AC Compressor Off
 

How can they check pressures when the compressor is not producing any pressure being off? Is there a specific method of recharging listed on the A/C decal underhood? On my 91 youcannot haveA/C related codes current in the system in order to have the compressor stay engaged while recharging. I would say the sensors are working because they provide the reading to the ECM to open that circuit, which they seem to be doing. And yes, the compressor dehumidifies the warm air directed to the winshield to speed up defrosting.

RE: Service AC System / AC Compressor Off
 

What codes are showing in the computer? Why are you taking it to a place that drains and refills motor oil?

RE: Service AC System / AC Compressor Off
 

when you push the button, the compressor does engage, it just doesnt stay on long. There aren't any codes being showed other than the Service AC from the tread.Express also does AC service, cheaper than taking it to Cadillac. $80 to diagnose.

RE: Service AC System / AC Compressor Off
 

"There aren't any codes being showed other than the Service AC from the tread"

I'm sure you know what that sentence means but it is a mystery to me. The oil-changers charged you $80 to tell you everything is fine? It isn't though, is it?Good-bye $80.I'd like to help, but you give very little to go by. You replaced sensors for some reason and the compressor cycles Off after a short run. That is a classic 'low refrigerant' symptom. There should be AC codes shown in the diagnostic readout.......

RE: Service AC System / AC Compressor Off
 

The codes statement was in reply to "what codes are showing" the only code I'm getting is Service AC System / AC Compressor Off which is the topic of this thread. Sorry for the confusion. I was saying that Cadillac charges $80 just to diagnose. I agree with the low refrigerant, in the past with other vehicles this was a classic and simple symptom and fix. Not with the Caddy. As stated, when hooked up to the machine and the compressor cycles on, it reads full at 2.0 lbs. I did the Off / Warm button diagnosis and no codes were displayed. In every catagory, it says No Codes.

RE: Service AC System / AC Compressor Off
 

Something is telling the system to shut-down the compressor or the compressor is shutting down by itself. No codes is pecuilar. How old is that compressor? Have you checked the voltage 'to' the clutch/compressor past the switch? Wiring/terminals clean/tight?

RE: Service AC System / AC Compressor Off
 

As far as I know Dave, its the original compressor. Not that advanced to check voltage and all, but if it comes on it should be getting power, shouldn't it? The connections are tight as the switches have just been changed. I will check the wiring harness to the compressor, but I don't think thats the culprit. May have to just break down and take it to Cadillac. There is a shop here who claims they know all things Cadillac. Their diagnostic is $78, but they will waive it if you get it fixed right then.

RE: Service AC System / AC Compressor Off
 

If there is voltage to get the clutch engaged, but then the clutch dis-engages: the clutch may be just losing power (the reason to check voltage),orif there is voltage to the clutch, but dis-engages,it's faulty.12yrs on the clutch and compressor is a good life-span. You might start saving for a replacement unit. New w/clutch $350. Reman w/clutch $250.

RE: Service AC System / AC Compressor Off
 

Does this car use refrigerant temperature sensors (thermisters)?

If so I would replace the Low side sensor. When these sensors start to wear out there resistance (ohms) starts to increase. and since the cars computer reads the change in voltage (variable resistance) to determine a temp. value. It therefor thinks you have a problem when in fact you don't because of the erroneous data it is receiving.

So, whats the function of the low side temp sensor?

It tells the computer when to engage and disengage the compressor based on the refrigerant TEMPERATURE not pressure. It has a set temperature range to do so which if I recall corectly is -1C - 11C (30F to 51F). So if it hit -1 it will disengage the compressor because it thinks the evaporator core is about to freeze up. Now remember the part about increasing resistance? Well It just so happens in these cadillac systems higher resistance means a LOWER temp reading. So as soon as then compressor engages I would bet money that the temperature value falls BELOW -1C therfore the computer shuts it off.

I would replace a $30 sensor before go any further.

RE: Service AC System / AC Compressor Off
 

My car does have the temp switches. One on each side of the orifice connector. I will give this a try. Thanks for the info. Will post the results.

RE: Service AC System / AC Compressor Off
 

I'll add my 2 cents. What amount of freon is listed on the yellow freon decal under hood? is it exactly 2 lb.? if so, then level is fine, if not then its either over or undercharged, which could be the whole problem. With the factory manual you can verify A/C pressure readings, both hi and low thru the DIC. The manual will confirm whether the system is reading correctly ruling out or confirming a faulty sensor. Every time my DIC reading states to service the A/C I get a F code which I erase. My system will only set this code when outside temp is approx. what my temp display is set to. I know my car is about 3 ounces low on R12 so its working as designed. The clutch is allowed to operate not by letting voltage reach the clutch but by a completed ground circuit. The ECU and BCM open and close grounds to provide power to components or to turn off components. To procede logically, you need the factory manual to confirm pressure readings and if they are not in spec the manual will tell you where to check next. This era of GM cars, Allante included, had an "orfice tube" that if partially plugged up with debris would raise pressures within the system and disable the ground circuit to the compressor clutch until that orfice was replaced, freon full or not. I find the Allante to be the best early warning system of any GM car of that era. 99.9% of the time the messages, codes are correct.You make reference to the "Cadillac book" do you mean the factory manual? Bottom line, without the factory manual either you or the A/C technician will get frustrated and throw parts at this car.

RE: Service AC System / AC Compressor Off
 

Yes I was refering to the factory manual. For some reason, I can't find the decal that tells me the proper fill level and such. As previously stated, I don't get any codes and strangely, I get this error message whether thesystem ison or not! Another odd thing Carnut, I notice that when the system does stay on for a minute or two, the air blows coldest when it switches back to Econ, go figure. Not constantly but for a few seconds, it is ice cold air coming out of the vents.

RE: Service AC System / AC Compressor Off
 

Also, the orifice was changed prior to my taking possesion of the car. It was replaced and the system was supposed to be vacuumed and recharged by the dealer. This was in May, had it vacuumed and recharged in June when a small leak was detected at the low pressure fill. Still to no avail.

RE: Service AC System / AC Compressor Off
 

How is the quicky lube getting hi and low pressure readings if the compressor kicks off? Why was the orfice changed? debris? The proper freon amount is listed in the FSM. I'm missing something here. If a worded message displays a code will set, Pressures are not monitored inOFF setting, but could be in ECON.

RE: Service AC System / AC Compressor Off
 

list year and model in your profile next to the 96 DeVille.

RE: Service AC System / AC Compressor Off
 

Not sure I know what you mean but its a 1996 Deville base model. It will run for a few minutes sometimes. The book says 2.0 lbs, which is what they filled to and what registers as full at recheck. And I know, thats whats strange to me. When the system is OFF, it will give me the error message. However, when I do the diag check (off and warm button) all categories say NO CODES. Not sure why the orifice was changed, but I saw it when they took it out, it was dirty. Didn't see it when they replaced it, just trusting that they did put in a new one.

RE: Service AC System / AC Compressor Off
 

Sorry for the mistake. I toggle back and forth between 3 Cad sites, thought is was an Allante!

RE: Service AC System / AC Compressor Off
 

Thanks for the tip. I think I finally got it! Stays on and blows pretty cool air. I didn't know you had to vacuum the system prior to changing these switches so I lost some refrigerant. But I think I have it back right. I may just go and have it vacuumed and refilled to be sure. But right now its blowing pretty good. Got my thermometer out and it got down to almost 40 degrees while wide open. I think that's pretty good, don't you? I'll keep you guys posted on the performance.

RE: Service AC System / AC Compressor Off
 

By the way, the temp switch was $33.87 + tax from the Cadillac dealer. FYI

RE: Service AC System / AC Compressor Off
 

as long as you pulled a vacuum and then charged into the vacuum you should be good.

I'm glad I could help cuz I went nuts trying to find out why my 90 deville was doing the same thing. I followed the diagnostic chart to the T and according to it I needed to replace a computer. Well, I'm glad I used the old coconut (my head) and figured it out.

What was stumping me is everything worked. ex. you turn on the A/C and then the computer sends the signal through multiple computers, relays, switches and whatnot to the compressor. the compressor would engage and then disengage like you turned it off. Which to me meant that for some reason the computer thought it need to disengaged the compressor. So I got to reading about the low side temp sensor and I redid the "sensor test" that diagnotic chart said to do. And acording to it the sensor was fine. Well I took a gamble (way easier then replacing a computer) and put in a new one. and it fired up and ran like a champ! I was so happy.

But now I have a leak in my evaporter. so I'm in the middle of putting in a new one. and then I will have one cold ass r134a conversion! Speaking of which if you get a leak in the evap. pay someone to do it.. It is the BIGGEST PAIN IN THE ASS.

RE: Service AC System / AC Compressor Off
 

Man you don't know how much I appreciate the info, it's been running like a champ every since. Saved me major bucks. Dealer and other shops charge around $80 just to look at it. No telling what hoops they have made me jump through. Experience is key. Good luck with the evap, let me know how it goes.