1993 Ford E350 A/C Not Cooling

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I have about 60psi of static pressure in the system. When I turn the ac on, the clutch engages but quickly cycles off at 85psi high side, 26psi low side.

I jumpered out the two pin pressure switch so that the ac clutch remains engaged. The pressures are 90psi high side and 14psi low side with the compressor operating continuously. This is the first time I have worked on ac. I would interpret this as both a bad pressure switch and low refrigerant. Does anybody have any other ideas?

The ambient temperature here is about 62F.

Thanks.
 
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The pressure switch is good and shutting off at low pressure to protect the compressor from damage. You are clearly low on Freon and need a recharge. Try adding a 12 oz. can of refrigerant (R-12 I suspect) to see if that will raise it up to maintain low side pressure in the 25 to 30 psi range when the compressor is running steady.
 
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Originally Posted By: Nukeman7
Try adding a 12 oz. can of refrigerant (R-12 I suspect)


I think the 93's were R-134a?
 
"Nearly empty" is a much better description of this situation than "undercharged". If it has worked properly recently, it has sprung a rather large leak.

The rapid cycling is normal when nearly empty. Do not jump the switch. It will start to cycle normally once charged.
 
The ambient temp is 62F. It has been converted to 134a according to a sticker under the hood but was originally R12.

I put very few miles on the vehicle and rarely ever use the ac. Maybe once every year or two. (I know that I should use it more.) The vehicle is 24 years old so I'm not sure if it's leaking fast or if it has just slowly leaked over time. I bought it 7 years ago and I'm not sure the ac worked all that well when I got it but I had other things to worry about. It is a 14 passenger bus that I built into a camper. We had a very hot spell last summer and now the wife wants the ac working for our vacation this year.

I already added 1 large can of refrigerant before I got my manifold gauges to try to diagnose the problem. It has a rear unit so takes a lot of refrigerant.

So, the pressure switch turns the compressor off when the pressure is too low. Does it also do the same when the pressure is too high?

Thanks.
 
Originally Posted By: NibbanaBanana
The ambient temp is 62F. It has been converted to 134a according to a sticker under the hood but was originally R12.

I put very few miles on the vehicle and rarely ever use the ac. Maybe once every year or two. (I know that I should use it more.) The vehicle is 24 years old so I'm not sure if it's leaking fast or if it has just slowly leaked over time. I bought it 7 years ago and I'm not sure the ac worked all that well when I got it but I had other things to worry about. It is a 14 passenger bus that I built into a camper. We had a very hot spell last summer and now the wife wants the ac working for our vacation this year.

I already added 1 large can of refrigerant before I got my manifold gauges to try to diagnose the problem. It has a rear unit so takes a lot of refrigerant.

So, the pressure switch turns the compressor off when the pressure is too low. Does it also do the same when the pressure is too high?

Thanks.
No, it is only a low side switch, which opens on pressure drop. If your gauges have a temperature scale, a decent starting point is the pressure which corresponds with 45F, as the system gets colder it will drop. In my experience the R134A adapter fittings are a common place for leaks.
 
Yes especially if you have a tall aluminum adapter fitting on the low side. Those are junk. NAPA may still sell the yellow steel ones that are much better.
 
Originally Posted By: NibbanaBanana


So, the pressure switch turns the compressor off when the pressure is too low. Does it also do the same when the pressure is too high?

no. Most r12 systems did not use a high pressure cut out switch. If the shop did the conversion correctly they should have added one.
 
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