Question about A/C pressures.

DEWFPO · Jul 13, 2016

As part of my maintenance I checked the low side A/C pressures yesterday and at 72F ambient, the pressure switch cuts the compressor out at 15 psi and cuts it in at 30 psi. My driver's side vent temp is 43F under these conditions.

I am used to automotive A/C systems and was expecting cut in at 40-42 psi and cut out at ~25 psi. So I checked the good book.....

On page 80-10-4 of the Service Manual states the compressor should cut out at 5 psi and cut back in at 20 psi. A few pages late on page 80-30-3 of the same manual it states the Low Side pressure's should be 15-33 psi.

So, the question is, is my system smack where it should be or is it slightly overfilled?

Thanks, DEWFPO

CreekyB · Jul 13, 2016

Here is a chart for refrigerants.

http://www.refrigerants.com/pics/ptchart.pdf

Superheat and subcooling measurements are the easiest way to check on charge adequacy. Just remember that most values you are looking for are under "perfect conditions" when checking charge using superheat or subcooling. Meaning that if the Condensor or Evaporator are dirty, filter if equiped is dirty, etc, then the values will be a bit off.

I tend to just get a decent heat load on it, 80-90 degree outside temps and turn it on. Once stabilzed, as close as you can get to a 18 degree difference between return (intake air) and discharge air temps the better you are.

Also you did not list what refrigerant is in there. 134a? Pressures and temps vary widely with refrigerants, which is why there are so many uses for all of them

Superheat/subcooling: Troubleshooting A/C Superheat, Sub-cooling & Delta

DEWFPO · Jul 13, 2016

Thanks for the links to the data and info. The system is R134a.

DEWFPO

RickB · Jul 13, 2016

At those pressures and with the vent running about 30 degrees below ambient I'd probably leave it alone.

dadster4 · Jul 13, 2016

RickB said:
At those pressures and with the vent running about 30 degrees below ambient I'd probably leave it alone.

Agree completely...The pressures at that ambient are fine, at a higher ambient they will be different, but the temperature drop is the best indicator that the system is operating well. 30 degree drop in temp is good.