Before taking it in, can I check anything? I looked at the fuses, don't see a problem, no obvious loose connections.

 

2 common reasons the compresoor does not kick on are:
1. Compressor clutch gap too wide (wear)
2. Low Pressure switch open

#1 can be tested by starting the engine and turning the AC on with hood open. Take a stick/screwdriver handle/etc and carefully thwack the clutch (the center section of the compressor pulley that is not moving if the AC is not working). If it kicks on, then the clutch gap is too large and you need to remove a shim behind the clutch to tighten the gap up. This is a 5 min job.

#2 Is from one of 2 causes, typically: Either you are low on freon, or the LP switch is bad. You can test this out by pulling the plug on the LP switch and jumpering the 2 pins in the connector (the harness side). The switch is located on the accumulator (receiver/drier) that is the tall cylinder near the passenger side firewall. If you jumper the connector and the AC works correctly (cooling the air) then odds are the switch is bad. A 2-second job to remove and replace and it's cheap. If the AC does not cool or you hear noises from the compressor that do not sound normal, then you are probably low on freon. Don't run for more than a few seconds this way or you will damage the compressor. If you are low on freon, you have a leak. If it is a slow leak, you can weasel-by by just refilling yearly for a while. If it is a big leak, then you need to fix it (and should find and fix it in either case anyways).

 

Thanks for the help. Can I add freon through the low side port without the compressor running?

Im fairly sure it is low, I was adding 1x a year and this truck has been sitting almost all summer while I have been driving another vehicle. I'll check the switch also.

 

Oh - you didn't say you have history here.... Yeah, odds are it's just low then. Go ahead and try adding more. It helps to warm the freon can in a pan of warm water while adding so it goes in better. You can try addin it with the engine off first and see how much you get in, but you'll probably have to get the compressor running to draw in what you need. If it still won't kick on by itself, You'll need to jumper the LP switch connector as above to trick it.

Give the whole story and you get better responses!

 

Right, I should have mentioned more. I guess I thought the compressor would short cycle as opposed to just not start at all if low freon were the problem.

Thanks again.

 

It will short cycle... until it gets so low that just won't kick on at all anymore. Based on your history, that's the likely culprit.