transmaster

The problem turned out to be the A/C Clutch Cycling Pressure Switch, which will take me longer to get drive the 5 blocks to my part store then it will be to install it.

NGM

Glad ya found it.. I didn't think it was going to have anything to do with the PCM...

transmaster

I really didn't either. I sure am happy, this is a 20 dollar part and I don't even have to monkey with the refrigerant to install it, it is screwed to what amounts to a extra large inner tube valve stem..

NGM

Yup.. Since there is a Shrader valve there is minimal loss of R134a

transmaster

The only other A/C system I am familiar with is the Frigidaire systems used in 1960's Cadillacs. Compared to them the system in this truck is simple but it sure would have been nice to have some of the features the system in this Ford has. The biggest pain in the *** was the 30 or so total feet of vacuum lines these Caddy's had to operate the various systems in the vehical.

transmaster

I am here to tell you I could not have done what I have done with the A/C system without Alldata DIY. Because so many states have made it illegal for the average home mechanic, no matter what their qualifications are, to work on A/C system it is hard to find good information about A/C systems anymore.

transmaster

really have to get a manifold gauge set for 134a. the one I have is for R12. I got the compressor going and I got lots cold air but only if by passed the new A/C clutch switch, the original was bad. The refrigerant charge was low so I charged the system up, at a certain point I found the clutch would cycle with the a/c clutch switch hooked up. Here is where I see a problem. The Clutch would cycle but what would happen is the pressure would rise to 45 psi ( this is low side pressure of course) which is right in the start of over pressure in the system. At 45 psi the clutch would kick in the pressure would then raise to about 47 psi and the clutch would disconnect. It did this continually, the clutch would stay not engaged more then a couple of seconds at a time. the compressor not being in operation long enough for the system to work. You can see why I need A proper manifold pressure gauge set for 134a. Could this be a bad high pressure switch? Does the High pressure switch sit on a Schrader valve? If it does I will replace it, if not I guess I will take the truck into the shop and pays my money to get it fixed.

NGM

Could be a blockage in the system. This would cause the highside to shoot up and shut the compressor off.

transmaster

I wonder if the orifice tube is clogged, anyway you look at it this is a job for a properly equipped A/C shop. If this is what is happening the system will have to be opened flushed out and internal parts replaced. With a 155,000 on the truck it wouldn't suprised if the compressor is worn out. When I get the manifold gauge this next friday then I can see what is going on on the high side.

wde3477

Not understanding how a rise in low-side pressure can cause the compressor to cut out. The low-side switch will kick the compressor out if the pressure drops too low. The high-side switch drops the compressor if pressure gets too high. It's been my (limited) experience that when the compressor cycles OFF or ON, the high and low side pressures move in opposite directions.

Any chance the system is over charged? 45psi on an R134 system relates to 50degF - kind of warm for the low-side, IMO. Perhaps inadequate airflows through the condensor coil?

I will say that I don't have a lot of experience with A/C other than with my truck and the related conversion from R12 to R134 - so I will gladly defer to the guys that work on this stuff for a living.