I have a 1999 that isn't engaging compressor. Not sure if it's due to low freon, bad switch, etc. how can I test?

 

You need a gauge set to test for refrigerant pressure.

 

As glc said... but do not buy a can of instant A/C and use that guage.... you need a proper gauge set.

In fact, the best thing to do is take it to a shop, especially one that deals with A/C repairs.

 

Does cruse and reverse lights work? If not check fuse #5 in fuse box under dash.

 

if you buy a can of instant A/C and use that gauge, make sure it reads no pressure or very low before adding freon to it. It should not take the whole can. If the ac worked last year then it should take less than 14 ozs. It is a good thing to see the high side as well, so you don't blow a hose and get hurt. Most shops charge $80 to do a recharge.

 

Perform at your own risk...

You can check the pressure switch by jumping the terminals. Remember if the system is low on freon this switch keeps the compressor from running. If the pressure is ok and you bypass the switch and it works then you found the problem.