Automotive Air Conditioning Information Forum

Looking for some help with my truck. We have had the truck for about a year and slowly over that time the air coming out of the vents has started getting warmer and warmer. I decided to see if I could fix the issue. I put the a/c gauges on the truck and here is what I the pressures read:

Ambient temp around 75, suction pressure cycling with the compressor was going between 20ish and 50ish and on the high side between 100 and 110. A pressure chart from acprocold.com had that as low for both sides and to add refrigerant. I added 12 oz and a little more from a second can and the pressure came up and the compressor stopped cycling. The air was colder than before but not real cold. I took the truck for a drive and when I got back and the put the gauges back on then the pressure was on the suction side was 35 and the high side had gone to 325. After idling for a minute the compressor then started to go back to turning on and off this time with the pressure on the suction side 25-62 (the compressor would turn on around 62 and then cut off at 25) and the high side was going back and forth between 130 and 150.

That is when I found this forum and this post https://www.autoacforum.com/viewtopic.p ... f250#p1024. After reading that I went back and started the truck back up and started doing the cycling of the compressor and then the high pressure started to climb along with the low side. The high side reached 325 and the low side around 30. I sprayed some water on the condenser and the high pressure came right down and the compressor started cycling again and then after a couple of minutes the pressure would slowly rise again but it never got back over the 300 on the gauge. One thing I found was some cold air coming out of the where two the lines run into a box or plenum (see the pic below). So perhaps there is a leak somewhere with the air duct.

It seemed maybe two issues were happening a) it was low on refrigerant and 2) perhaps the condenser was not 100% or the orifice tube need be replaced. I was just about to add just a little more refrigerant when I notice the low side over 100 and the compressor no longer coming on.

Update: After sitting for about 45 minutes the compressor has started working again.

Well, outside of the obvious air leaks on the evaporator box you need to deal with, there are a couple of other issues.

1) The cycling switch hysteresis. This is a problem I have seen with this vintage Ford before. It should not be waiting for 60 psi to turn back on. It may also be responsible for the compressor failing to start at all, but there are other causes for that.

2) The compressor failing to start when hot. This is likely caused by an excessive clutch gap. This is adjusted by moving shims, and is completely normal wear over time in CCOT systems. Check the clutch gap with a feeler gauge, and reset it if worn. Regardless of other work, this should always be done to eliminate the variable on a system.

3) You have no idea how much refrigerant is actually in the system. It could be undercharged or even overcharged. The best way to find out would be to recover the system & weigh the charge.

4) Your fan clutch is suspect. A 12 yr old F250 has to have at least 100k miles on it. Fan clutches wear out, and when they do the A/C suffers while the engine still cools well enough. Your 375psi spike could be compromised condenser airflow.

I would be inclined to recover the system, replace the cycling switch & inspect the orifice tube. If large debris or evidence of sealant are present on the orifice tube, then further work would be required.

If the orifice tube is less than 20% covered in small debris, I would replace it & add and ounce of oil along with dye before closing the system back up. Then charge it by weight & run it. I would check carefully with a UV light after a couple of days for any leaks that might need further service.