I am recharging my A/C. What is the correct psi of freon? The temp here is running around 90. When I am charging the psi goes from compressor kicking on at 65, and going off at 20, and cycling on and off every 10 to 15 seconds. Any info would be great.....

 

you want it above 30 lb psig on the suction side. 134a you will need to have vehicle at high idle to see what the pressures are doing . simulateing driving down the road pressure.

I dont have any charts to determine what it should read at a given ambient temp.

 

OK Just back in..... the psi on the low side is 45. highside is ice cold but blowing ambient temp. It's around 75 here today. Is the evaporator plugged, if so how did it plug up? How do I unplug it? Do I have to remove it? Thanks so far!

 

Are you sure that the compressor was cycling on when you took the low side reading. High side should be real hot to the touch. low side cold. Pressure could be to low to kick the compressor on.

 

Let me add something to this. You have to have either the fan locked up or a fan pushing the air through the radiator. Without this you will not get accurate pressures and will be low on freon. Mine starts working well at or above 45 pounds low side. And still it will sometimes drop out at idle on a hot day. I think part of that is the fan not running.

 

I might have grabbed the wrong one, compressor at least sounds like it's cycling on and off.... click 10 to 15 seconds later click and so on! I had the truck at 1800 RPMS, it'll run close to that running down the highway at 55mph, the fan was pulling air through the condensor and the radiator. I don't know how the evaporater could plug. Maybe frezze but I would expect to see some ice coming from somewhere.....

 

its been a while since i messed with A/C but it sounds like you are cycle on and off for low pressure. did u add freon? 12 or 134? you should have 20 to 30 on the low side and 200 to 240 on the high if the high side is much higher than that you have a blockage. there is a filter by the reciever dryer thats can get plugged.

 

My orfice in the high side dissloged and stuck in a 90 degree turn right in front of the air filter box. Causing a blockage replaced the high side line recharged good to go. Just a thought..

 

Need to fill in your signature, what year is your truck?
What type of gas are you trying to use? R-12, R-134, R-406, R-409.
From the what you are describing, the low pressure cutout is working and the system goes into a suction and cuts the compressor till the pressure rises then it restarts. And if the evap temps are hot, would also indicate a low charge. Here is a link to a temperature/ pressure chart.

http://www.aircondition.com/pressure.htm

Without knowing which gas I would not know how you are to charge the unit. Going by pressure is a pain and not accurarte because of the temperature to pressure ratio.
Do you have a sight glass to check, If you are using a drop in it is hard to do because you can't just "top off the system".
They usually only charge to around 80%.
Check all of the hoses and fittings for a oily mess and you will find the leak.
Jim.

 

Sorry, for not having my sig updated! I'm using 134a. According to everything else I've read I should be at 30 to 45 psi. Did I see / read the chart right I should take it to 104@ 90 degrees / 79 @ 75 degrees? If so I'm no where near that! I was at 60/65 @ 75.... I had this thing to a mechanic he says the evap. has a small pinhole leak, after he charged me 100 to fill the system, and I had to take it back to him. When he had it I couldn't tell where he had taken anything apart... dash, duct, nothing! And I'm not seeing any evidence of a leak ( no oil ). That's why I came here! I know the guys on here are usually better than the mechanics that I deal with, always more honest! I'm tired of dealing with these buttheads, dealers and the small hometown guys!

 

Just for information...

I had a small shop in Boise Idaho put in 1/2 # of R-134a.

The correct pressure he quoted was 35 PSI on the LOW SIDE and about 250 PSI on the HIGH SIDE.

Then he used a infrared temp gun... The air coming out the vents at...

IDLE = 25*F
2K RPM's = 19*F

I could pull the cab temp down to 70*F easy now! Yeah... That a freezer now in 105*F Boise Temps...