'05 Caddy DTS Compressor Did Not Shut Down

[jjm01]

2005 Cadillac DeVille DTS
60,750 Miles

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

Last fall, I noticed the compressor discharge line was leaking - didn't need to break out the leak detector with the green oily goo screaming leak (see photos below). And of course, within a short time thereafter, air from the left vents were warm, followed by all vents being warm. But with winter coming, I figure who needs A/C now, I'll deal with it in the spring. Ironically, no codes and no "SERVICE A/C SYSTEM" message ever displayed on the DIC accompanied by compressor lockout.

Well, my laziness cost me in the form of misery Thursday with the mercury climbing to near 80F... but at least I had the cooled seats. So now I decide to hook up my gauges to see what's going on. 45 PSI static pressure with the engine off - system is pretty much empty. By the way, I hate the fact this vehicle doesn't have "real" service ports, with the high and low side ports inches apart on the liquid line.

I start the engine, and get pressure readings of 40/90 at idle, and the compressor is running continuously! Still no codes are present, and the BCM was indeed commanding the compressor on (not like a stuck relay), according to the scan tool.

Since there was next to nothing left in the system, I discharge the system, and finally the compressor disengages and won't re-engage. With an empty system, still no codes and no "SERVICE A/C SYSTEM" message on the DIC, I pull a vacuum on the system, start the engine (not a great idea I realize), and still no codes or message (compressor remained disengaged).

In the interim until I replace the discharge line, accumulator, OT, and all applicable sealing washers and o-rings, I inject 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! Never seen that happen on a Caddy! After the full 36 oz charge goes in, pressures were 40/235 at about 2,000 RPM, and vent temps were 38-40F. The compressor would now also cycle... though it ran continuously with a virtually empty system!

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

Since I'll be pulling the discharge line, might as well replace the pressure switch while I'm at it, but something tells me it might be something else. I'm really lost on this one.

I got the FSM, which confirms a low refrigerant code should've set as I suspected it should, but as stated mine never did.

Any ideas guys and gals?

Thanks!

Joe

[jjm01]

Update...

Pulled the electrical connector off the trinary pressure switch (on the discharge line), 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 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 trinary 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.

I'm probably the only one that ever had this type of failure... just my luck. Good thing this fault didn't cause the expensive Mistubishi scroll to seize up. The OT inspection will reveal if any damage was done.

Joe