I have a 1998 4.2L F150. I have had it for 8 years and know the AC has never been charged since I have had it and the AC has never really worked. Today I decided to charge it but the reading was way high over 100 psi on the low valve side (in the red danger zone) so did not add anything. I know it was the low side I was checking. Any ideas? Could it have been overcharged for 8 years? what now.

 

That pressure sounds okay if the compressor is not running. You need to have a gauge set that reads both the high and low side. Perhaps you should take it to a shop that knows what they are doing?

 

yep, the first thing to check is to verify if the compressor is running. Look at the front to see if the clutch is spinning. I'll bet it isn't running.

 

Like glc said, take it to a shop that knows A/C.

 

If the compressor is running at 100 psi low side, sounds like a bad valve.

 

The compressor wasn't running, therefore he was reading static pressure which, for around 90°F would be....drum roll.... a little over 100 psi.