2016 Cascadia DD13. No power to Air Compressor.

System pressure is 100% affected by ambient temperatured and humidity. The A/C high and low sides will run at higher pressures in higher temperatures and higher humidity. Manufacturers will normally provide a spec in their service manuals for pressure readings at various temperatures and humidity levels and the expected temperature at the vents.

Seeding just wrapped up, tons of A/C calls the last few weeks. Not fun spending 12 hours a day in a cab that's 80% glass in the hot sun with no A/C.

 

Static pressure with the system equalized only tells you there's some refrigerant in the system. It will not tell you if the charged amount is correct.

I was at a machine the other day, 70 PSI equalized high and low. Compressor on, low side went to almost 0 PSI instantly. Fixed the leak, recharge and good to go.

 

On cars I've figured about 115ish on the hot days to be fully charged. But they only hold slightly more then a pound.

The last semi was a daycab holding 2.25 pounds and was about 140.

I would imagine the suvs with rear ac holding about 2 pounds are probably close to that.

I don't know about sleeper trucks holding 4 pounds. Been about 10 years since I screwed around with one of them.

 

Big farm tractors are dang near 5lbs. But they've got a ton of glass so the A/C has to work really hard.

 

I don’t know about that. When I unplug mine, compressor won’t run. If the hi/lo switch is bad, depending on which side of the switch is not working. Lo side bad, I can jump the plug with a paperclip and turn compressor on. High side bad, compressor runs constantly unless I unplug the switch. Are you sure you aren’t unplugging the fan switch? Not the pressure switch?

 

Ok, I missed this. So it’s working fine now? Bad wire repaired? Didn’t add any refrigerant. Not overfilled? Compressor and fan cycling normally at idle? Good to go?

 

Every Freightliner sleeper I’ve seen holds just under 4 lbs. Usually it’s 3 lbs. 8oz. (56oz.) I typically use 5 cans@ 12oz. ( 60oz.) Bleeding the air from the line with each new can. Works out perfectly every time. Possible slight overcharge has no effect.

 

4 Oz. Over on a 4 pound system not a big deal.

4 Oz. On a car 1 pound system. Very big deal.