Recharging AC in Truck - Questions

[kevinstan]

Anyone have any experience with this? I replaced the AC compressor on my 2007 F-150, added the 8oz of PAG46 oil to the compressor when it was changed - then hooked up the gauges and added my R134-A while running the AC on high... Compressor clutch finally kicked in and it started blowing cold air again. Watching the gauges it will go down to around 25 PSI while the compressor is running, then the compressor will cycle and stop - which then the system goes to around 55 or 60 PSI then the compressor clutch engages again dropping it back down to around 25 PSI and it starts over. The AC is blowing cool air, but I feel like it could be cooler - though I don't want to overcharge the system either. I have looked online and cannot find anything definite about low and high PSI, only LBS measurement for the R134-A. Can anyone tell me what PSI levels are normal for the cycle? And if I have not enough or too much currently? Thank you in advance!

 

[Artfuldodger]

I'm no expert but it appears to be a bit undercharged. It would be better to also monitor the high side from an overcharging safety aspect. Some other factors to consider is the idle speed and outdoor air temperature.

I think you are suppose to rev up the engine a bit which will pull the suction pressure down.

The suction pressure should be 40-40 psi at 80 degrees outside and 45-55 psi from 85 degrees to 95 degrees outside.

You could add a little more to at least keep it cycling as much.
I'm not sure how often one will cycle at idle when properly charged. Maybe someone else will chime in.

 

[Jack Ryan]

Anyone have any experience with this? I replaced the AC compressor on my 2007 F-150, added the 8oz of PAG46 oil to the compressor when it was changed - then hooked up the gauges and added my R134-A while running the AC on high... Compressor clutch finally kicked in and it started blowing cold air again. Watching the gauges it will go down to around 25 PSI while the compressor is running, then the compressor will cycle and stop - which then the system goes to around 55 or 60 PSI then the compressor clutch engages again dropping it back down to around 25 PSI and it starts over. The AC is blowing cool air, but I feel like it could be cooler - though I don't want to overcharge the system either. I have looked online and cannot find anything definite about low and high PSI, only LBS measurement for the R134-A. Can anyone tell me what PSI levels are normal for the cycle? And if I have not enough or too much currently? Thank you in advance!

If you've got 10 - 15 degree drop in temp between the ambient air in the cab and the cold air coming out the vents, it's good. If less, it needs more.

 

[Casey81]

Did you pull a vacuum on the system before you charged it?

 

[kevinstan]

Yes - sorry I left that part out. I did pull a vacuum on the system first. Now I am just trying to charge it back properly.

 

[GA native]

You are still undercharged. With a proper charge the clutch will stay engaged.

http://acprocold.com/faq/r-134a-system-pressure-chart/ Here is a pressure chart for you.

 

[GoldDot40]

Cooler ambient temps will cause one to cycle a little more often. On a real hot day, it may not cycle on/off much at all.

Another part to pay attention to is the air temp at the vent with AC on max with the recirc on. Most the ones I ever did were blowing a nippy 38-40*F when they're at optimum charge regardless of outside temp.

 

[NE GA Pappy]

run max air, coldest setting, highest fan. You should be reading around 50 to 60lbs suction when it is running. High side will be much higher... probably in the 200 range

 

[transfixer]

I'm an auto tech by trade, although air conditioning isn't my specialty, I've done a good many coversions, and replacement work as well. I always try to get the low side ( suction side) to stabilize around 40 to 45, while watching the high side, on a day when its 75 or 80 degrees, I don't want the high side to go any higher than 200, and I'd prefer it stay down around 175 or so, because during extremely hot weather the pressures increase, and you really don't want your high side to run above 225 constantly in hot weather, ideally it should peak out no more than 200 psi, higher than that will cause premature wear and stress on your compressor.
As you put more Freon in the low side will slowly increase, but so will your high side, so try to keep an eye on both. I've sent many out the door with only 35 to 40 psi on the low side, and freezing cold air, with the compressor clutch staying on , a lot of it depends on the system of the vehicle.

 

[NE GA Pappy]

because R134 doesn't carry oil mixed with the coolant, if you run the system with a undercharge, you are also running the compressor low on oil. It doesn't matter if you added oil to the system. The oil molecule can only travel the system attached on top of the coolant molecule. So if there isn't sufficient coolant, then there can not be sufficient oil carried thru the dryer and expansion device to properly lubricate the compressor.

 

[EuroTech]

38 to 42 and 250 about three cans