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'05 Caddy DTS Compressor Did Not Shut Down

JJM on Fri April 11, 2008 4:44 PM User is offline

Year: 2005
Make: Cadillac
Model: DTS
Engine Size: 4.6L
Refrigerant Type: R-134a
Ambient Temp: 78
Pressure Low: 40
Pressure High: 90
Country of Origin: United States

I'm embarrassed to ask for help, but I'm really stumped... perhaps it's time for me to hang-up my gauges.

You might recall from my previous post '05 Caddy DTS Springin' Leaks Already that the compressor discharge hose appeared to be leaking... on a less than 3 year old car. Indeed it was, because within a short time thereafter, air from the left vents were warm, followed by all vents being warm. But with winter coming, why bother I thought.

Ironically, no "SERVICE A/C SYSTEM" message ever displayed accompanied by compressor lockout.

Well, my laziness cost me in the form of misery yesterday as the mercury climbed to near 80F... at least the seats cool though. So now now I decide to hook up my gauges to see what's going on... 45 PSI on both sides. It should also be noted that there doesn't seem to be any "real" service ports on this vehicle. The high side port is on the condenser RETURN line and NOT on the discharge line. The low side port is a few inches downstream of the high side service port, right after the OT. No service port on the suction line... at least that I could find. So the pressure readings on this vehicle seem to be meaningless.

I start the engine, and the get the pressures above and the compressor is running continuously. No codes are present, and the BCM was indeed commanding the compressor on.

Since there was next to nothing left in the system, I discharge the system (at most a few penguins might've gotten dizzy), and finally the compressor stops and won't re-engage. But still no codes and no "SERVICE A/C SYSTEM" message. I pull a vacuum on the system, start the engine (not a great idea I realize), and still no codes (compressor remained disengaged).

I add 1 oz of PAG 46 to the system and weigh in 36 oz of R-134a. As the charge is being drawn in (engine running) the compressor engages... without clearing any codes, pulling the battery, etc. After the full 36 oz charge goes in, pressures were 235/40, and vent temps were 38-40F. The compressor would now also cycle... though it ran continuously with virtually no R-134a.

So while I know what to do to get cold air (replace the discharge line, accumulator, OT, add oil, vacuum and charge), my concern is protecting the system in the event there's a future leak. It seems there are only two sensors, the three wire trinary pressure switch in the discharge line like the V5, and a low temperature (not pressure) switch in the suction. I'm thinking it's gotta be the trinary pressure switch, but the compressor does cycle, and the system will shut down with zero charge.

I'll probably just replace the trinary pressure switch since I'll be pulling the discharge line, but something tells me it might be something else.

Any ideas guys?



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Edited: Sat April 12, 2008 at 1:06 AM by JJM

Chick on Fri April 11, 2008 5:17 PM User is offlineView users profile

Your high side port is ok where it is, not a return, still pressure but on the outlet side of the condenser. Many cars are like that.., and as many cads do, the low side is on the same line?? then the O tube is in the middle of the ports. The switches in the lines should be thermistors, although I haven't worked on one of them..If they are thermistors the measure both refrigerant pressures and temperture.. and also cycle the compressor.(refrigerant not cold, won't cycle) If you have a cycling switch, it's really a low pressure cut out switch, just looks the same..Gonna need a shop manual for that one.. You obviously still have a leak, rough working in a closet, Probably more room in a closet...

Email: Chick


Freedoms just another word for nothing left to lose

TRB on Fri April 11, 2008 7:12 PM User is offlineView users profile

BAT Auto Rocks


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NickD on Sat April 12, 2008 7:36 AM User is offline

In the 92, the low side thermistor if showing a higher than normal temperature with the compressor running kicks on the Service AC soon lamp, a mechanical pressure switch in the 2-8 PSI range with other considerations, ambient temperature, compressor running, kicks on both the service lamp and shoves the climate control into Econ mode.

Now you know when the ambient temperature is -12*F that low pressure safety switch is going to be opened with 0 psi, so it's not just the switch that determines if the CC is kicked into Econ, has to be a combination of things to set it off. All this can be tested without a scanner in the comfort of the drivers seat by playing with the CC buttons, a bit much for me to remember so carry a code book in the glove compartment.

So what about your 2005? Need a GM Tech II scanner with the AC module? With the 92 can go out after the car sat all night and if the ambient is say 14*C, every thermistor and there is a bunch of them should read 14*C on the FMC display, don't need a scanner nor need to search all under the hood for the location of these things unless one of the thermistors shows a different temperature. Are you really going to replace your trinary switch on a hunch? And since the 92, did Caddy give the owners more or less headaches?

Yeah I had my problems too, new blower motor about 10K ago, dirty compressor relay contact, lost 8 ounces of R-12 since new, and now the blower module, but nothing like yours.

TRB on Sat April 12, 2008 9:48 PM User is offlineView users profile

Joe did you look at the compressor circuit wiring diagram?


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JJM on Sun April 13, 2008 11:34 AM User is offline

Indeed BAT Auto does rock... would be nice if I knew what forum I was on. Guess the heat and no A/C had me dizzy.

Call me old fashioned, but I like my service ports as close to the compressor as possible. I don't see how pressure readings can be meaningful with this setup:

Chick you have it right: From right to left in the photo, there's the high side port on the liquid line, followed by the OT in between, then the low side port... all within inches of one another.

What I refer to as the trinary pressure switch is not at all a thermistor, it senses only pressure, which can be read from the Tech 2. If the system was working as designed, it should've set a P0532 (A/C Refrigerant Pressure Sensor Circuit Low Voltage), the compressor should've been kicked off, and the "SERVICE A/C SYSTEM" message displayed on that dash. No code ever set, but the compressor did mysteriously disengage when the system was fully empty.

Tim as for the A/C wiring, it's pretty much straightforward.

- The trinary pressure switch on the discharge line is wired into the PCM.
- The PCM outputs the compressor signal to the A/C relay.
- The A/C relay powers the compressor coil (there is a over-temperature protection switch that opens power to the A/C compressor).
- The PCM communicates via the Class II network with the DIM (Dash Integration Module) and IPM (Instrument Panel Module).

- The low temperature (not pressure) switch in the suction line is wired to the DIM (Dash Integration Module). Module communicates over Class II with the PCM and IPM.

- The A/C control head is wired to the IPM (Instrument Panel Module), which communicates with the DIM and PCM over Class II

I'm going to try disconnecting the trinary pressure switch and see if a low refrigerant code (P0532) sets, as well as disconnecting the low temperature switch which should set a P1531 code.


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JJM on Sun April 13, 2008 2:49 PM User is offline


Pulled the electrical connector off the trinary pressure switch, and sure enough, the compressor kicked off, the "SERVICE AC SYSTEM" message appeared accompanied by the "A/C OFF" indication on the control head. Scanned the system and sure enough the P0532 code was present. I did not, however, need to clear the code for the compressor to re-engage; merely plugging the connector back in restored normal operation, and P0532 became a history stored code.

I assume the ternary pressure switch is indeed bad, either that or the factory harness is miswired... which would seem highly unlikely. I'll replace the switch along with the leaking discharge line, accumulator, OT, sealing washers, and o-rings, followed by balancing out the oil, pulling a deep vacuum and charging to spec. I'll be sure to test the new switch on the empty system first, to see if P0532 sets like it should.

Thanks again guys!


When considering your next auto A/C purchase, please consider the site that supports you:

NickD on Sun April 13, 2008 3:15 PM User is offline

Could be an intermittent connection, typical with GM. You have a Tech II scanner? Where do you live?

mhamilton on Sun April 13, 2008 5:50 PM User is offlineView users profile

Call me old fashioned, but I like my service ports as close to the compressor as possible. I don't see how pressure readings can be meaningful with this setup:

Hmmm... that is a new one to me. I know most all the big GM systems I've seen had the high side right before the o-tube. But the low side was always on the accumulator. The older Cad models had the accum cut into the surge tank (and low port on the suction hose)

NickD on Wed April 16, 2008 6:32 AM User is offline

Finally removed one of the struts in my 04 Cavalier, guess what, no camber adjustment, bolts were splined with a force fit for both the strut and steering knuckle, only alignment adjustment is the toe-in, the shop manual lies. All the rubber, strut, seats, spring, were in good shape, but the thrust bearing never was greased with 26 rusty balls inside. This thrust bearing was snapped into the upper spring seat made of plastic, that's right, plastic with the top of the spring coil pressed into it that I could unsnap with my fingers.

A rubber seal sat on top of it that had an embedded upper race, that was also easy to snap off, dealer wanted 76 bucks for this plastic seat and thrust bearing assembly, wouldn't just sell me the thrust bearing, so I cleaned it and packed it full of thick axle wheel grease, that quieted it down. Doing the other side today.

Thrust bearing was stamped, Made in China, ha, was time I felt like placing a sign Made in America on some nice looking Chinese gals. In a like meaning, they are hanging a sign on us, Made in China, so just bend over.

Great design on the bearing, was quiet until I just got passed the warranty period, just barely 500 miles over the limit. Dealer was delighted to tell me my car is out of warranty. Don't nearly the problems you are having Joe, namely because my car doesn't have all that stuff, if you ain't got it, it's not there to go wrong. Still a nice comfortable little car, and it gets us there. Have to put on 900 miles next week just to make immigration happy, also have to bend over to please them.

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