double bogey

My 2008 screw. The ac has been running fine since I bought it new. Yesterday afternoon it started acting up. It would cool driving 40 mph, but not at a stop light (idle). Today, it would work at idle, but not at speed. Put gauges on it (I am a 40 yr. hvac/refrigeration tech) and it would pump, but it was obviously not cycling on the lp control on the accumulator. The fan clutch would pull in, and the fan would run. Low side 40 to 58 lbs, high side 150 to 275 lbs. Looks like the high side has a transducer.

Now the compressor will not come on, standing pressure 129 lbs.

Help!!

Hongstertruck

Did you put some refrigerant in lately?

double bogey

No it has never had any refrigerant added. I am going under and see if the compressor clutch is getting power. Hard for me to do, had a tumor on my spine removed in February, still don't have strength back.

double bogey

Ok, I located a wiring diagram. I have power to one side of the coil and contacts both on my ac clutch relay. On the coil side, there is a pink/yellow wire that goes to the powertrain control module. If I disconnect this and apply ground to his side of the coil, the relay pulls in, and the compressor runs. What is my next step? How do I convince the powertrain module to let my ac run?

Mod (Ret.)

There's only one thing that comes to mind that would have the PCM tell the A/C compressor to shut off, and that's if it thinks the throttle is at full open position. If you stomp the "drive by wire" pedal, the PCM shuts down the A/C clutch.

double bogey

I have been wracking my brain trying to figure this out, and while driving back from a ranger game tonight, a sentence in the sequence of operation popped in my head about the WOT switch cutting off the ac. Is that switch on the gas pedal, or the throttle body? got at least one more check to do tomorrow. I have the service guide, but without the analyzer, I can only perform the electrical tests.

HarryK

Interested in this also, AC cut out in 93 degree heat in heavy traffic (20-45 mph). Thought it had developed leak except when I went to check it ac couple of hours later in driveway it worked fine. Is there anything like 'heat soak' to disable it for a while?


Also, found some info about a TSB but maybe only for 07-08 where there is a temp cutoff to the compressor if the underhood temperature reads over 170 degrees? Can anyone look this up? If so can we bypass the sensor?

Thanks

double bogey

Well, it looks to me like it doesn't have a wot switch. It must read the signal at the tpi. I did a tpi calibration, but it still will not work. Looks to me like it could be: the gas pedal control (this works the throttle body with a motor), the TPI, the EMYC, or the PCM. Or it could be a broken or shorted wire. Wish I had the correct analyzer.

Hongstertruck

it could be low pressure is what cause your A/C compressor not to kick in. You can try to override the pressure switch and see if that logic is OK.

I know you have checked pressure but how could you check pressure when compressor is not kicked in?

Since you have the equipment to do it, I would vacuum down the system for one hour and make sure it maintain 30 inch of vacuum, then refill and see what happen.

Hongstertruck

Your problem appears to be correct with TSP. The design of the cooling fan in our truck is a piece of ****. Can't handle hot weather in stop and go traffic. You need to upgrade to 2011 electric fans, it's pricey but man worth every dime.