I have a 1993 Ford F-150 XLT 5.0L. About 4 days ago the A/C just started blowing warm, so I turned it off and rolled down the windows. When I got home I went to add more R-134a. I started the truck, put it on MAX A/C and noticed the compressor will not engage, according to the low pressure the pressure was 100psi, now I know that is kinda misleading since the compressor didnt turn on. Any help or knowledge would be appreciated, thanks for reading

 

The compressor will not run if low on freon... if it is low... you have a leak somewhere.

 

But how do I check for sure? When I put the gauge on it says 100psi. Do I just add more in hopes it will kick on?

 

Disconnect the low pressure switch on the accumulator and jumper the connector with a paper clip or similar and watch the low pressure gauge it should stabilize somewhere between 25-45 psi depending on ambient temp. If it drops below 25 and is not blowing cold add some Freon. If the compressor don't engage bump the clutch hub face with a wrench or other while the engine is running, careful of the belt. If it kicks in and stays engaged your field coil is bad or the air gap too wide.

Lots of other diag after that but that's a starting point.

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I tapped a screwdriver on the condenser, as soon as I did the compressor kicked on. It seems like its the pressure switch that needs replaced. The condenser says R12 on it but the low pressure connector fits R134a. In a previous post on here guys said since the R134a fit its unlikely that it is R12 and it has been converted to R134a already. So when I replace the pressure switch do I get an R12 since thats what the canister is or do I get a R134a since that is the freon inside?