Hi All,
I'm green when it comes to diagnostics with AC systems...

Had a trip out to the desert this weekend and vent temperature from the AC was barely cold. I decided to look for a sight glass to see if maybe the refrigerant was low, only to find out these trucks don't have one. What I did notice was that in Max AC mode, the compressor was cycling on and off every 3 seconds. On for 3 seconds, off for 3 seconds and repeating.

Got home and hooked up the manifold gauge set I had bought and never used before, and checked the workshop manual, section 412-00-146 (Refrigerant System Tests). Ambient temperature was 65F, high side when compressor was running was at 100psi, low pressure was at 38 psi. When compressor OFF, I read 85psi on high and 38 psi on low. The manual provides some diagrams based off ambient temperatures but doesn't say what reading you should use (when compressor off vs on, I am assuming when it is running...). From the diagrams, which are of somewhat low resolution, it appeared that system level was low.

I added a half can of some refrigerant with UV dye to try and track the leak. This fixed the AC vent temperature (ice cold now), but the compressor now is just ON and doesn't appear to cycle at MAX AC mode. It cycles once every 30 seconds while in normal AC mode. While compressor is on, I am reading 125psi on high port and 22 psi on low... High side is good, but now low side is lower than spec.

1) I realize I need to properly evacuate the system and recharge. I still can't find the page that tells me how much to add... I'll keep looking on that, but if anyone knows, please post. I have a vacuum pump from HF, need to read up on how to do it.
2) I want to run the AC with dye to hopefully find the leak
3) Will I damage the compressor while it is at this stage?
4) Any advice?

Thanks

 

At this point you won't damage the compressor, I'm guessing it's still a little low on refrigerant.When it's running is the suction line (low pressure line) cold and sweating at the compressor if it is it's a sign it's full or close to full of refrigerant.

Denny

 

There should be a sticker on the core support that tells you how much refrigerant (134a in this case) the system holds . It’ll be in weight not volume, so you’ll have to figure out the volume needed to get the specified weight.
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