A/C Compressor Issue

Hey ALL!

I'm having a problem with the A/C compressor on my 2005 Freightliner Century. Basically, the compressor does not turn...

First of all, the system is fully charged with no leaks. Next, with the system running, I pulled the connector to the compressor and checked for spark and there's nothing coming out. So, I ran a jump wire off the alternator to the compressor and it will turn. So I then checked the HVAC relays in the fuse panel and I do have spark there. I'm guessing the problem must be "inline" maybe with the binary sensor? Or occasionally the truck does run warm... 220 degrees. I have read about the "chain of voltage" passing from the dash switch to the compressor and apparently it passes thru the thermostat along the way? Could a faulty thermostat be responsible for all my problems?

Thanks for reading!

 

Hey GrapeApe thanks for your response!

I know the system is charged because it said "full charge" on the gauge that I used to put R134a into the system. Afterwhich, the A/C worked for 1 day just fine. The following day the compressor would not turn. So I put in a can of stop leak with dye (thinking I had a leak) followed by another can of R134a. Again the system worked for 1 day. However, the next day the compressor would not turn. So that's when I began to suspect that my problem was electrical. I pulled the connector to the compressor and I found that there was no spark. I then ran a jump wire from the alternator to the compressor and it turned. So my next step was to go inside the cab and check the HVAC relay and it had spark. So my assumption was that I'm losing power somewhere between the switch and the compressor.

That's when I came across an old post referring to the order of voltage for the A/C system.... "Columbia AC problem, make sure you have 3.75 lbs of refrigerant in system, depending on if you have blend air but basically, voltage goes from switch, to thermostat, to binary switch on low pressure line to compressor."

Now maybe I'm wrong for even mentioning the part about the "thermostat" but it seems like there's a definite correlation between the compressor issue and the truck running a bit warm because they started about the same time. And at this point I'm just looking for any possible solutions... man it's HOT over here in the desert!

Your thoughts?

 

Ok thanks. Any idea where I might locate the low pressure switch?

In the meantime, here's the the last 6 of the VIN #U38034 in case anyone out there can pull a schematic? Anyone... please!!!

 

Hey GrapeApe, I think I found the problem and its not electrical...

Just for the hell of it today, I decided to add another can of R134 and just as soon as I started putting it in the system the compressor turned on. So apparently the system was too low for the compressor to kick in?

 

10-4 bud! Thanks for all your input!

 

Hey GrapeApe are you out there? I put a set of gauges on the A/C system this morning. I was wondering if you or anyone else can help analyze the results?

"Static" Readings:
(Low) Blue - 41 psi
(High) Red - 31 psi

"Running" Readings:
(Low) Blue - 3 psi
(High) Red - 85 psi

I also have another 01' Freightliner Century that I also put the gauges on to do a comparison...

"Static" Readings:
(Low) Blue - 100 psi
(High) Red - 100 psi

"Running" Readings:
(Low) Blue - 13 psi
(High) Red - 175 psi

At this point I'm not sure what is correct? The second truck does "okay" as far as cooling the cab but the numbers seems strange... especially the static readings.

Any help would be appreciated!