Basically how can you tell if it's a bad compressor vs. freon leak?

The low pressure cutoff switch keeps the compressor from running and damaging itself.

Bad compressors usually make a grinding/clunking/loud sound or I've seen them completely locked up.

Opening up the system and finding metal shavings is a telltale sign. There was a post here a while back with a picture of an orifice tube filled with them.

You'll need to throw a set of gauges on it to see your pressures.

https://texags.com/forums/46/topics/3145841 Has some info.

It's not supposed to

No, it won't.

You can short circuit the LP switch and force the compressor to come on, but without a fluid to compress (and the oil to lubricate it) you run the risk of damaging/destroying the compressor.

More than likely, you have a leak at A) a seal in the system (gasket, o-ring, interface) or B) transition place (metal to rubber, etc.)

Third and less likely option is Schroeder (sp?) valve. They will leak a tiny amount; over time, the tiny amount adds up to the full amount.

~egon

87IE said:

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You'll need to throw a set of gauges on it to see your pressures.

https://texags.com/forums/46/topics/3145841 Has some info.

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What will gauges tell me? If there's pressure then a bad compressor? No pressure then low freon?

The gauges will tell you the pressure of the system, If it reads 0 then you know you have a bad leak and the system is empty.

If the low side reads lower than your low pressure shutoff switch is set at (I'm not 100 % sure what that is for your vehicle but I usually look for 30 psi) then your compressor won't kick on so you can't rule out the compressor being bad.

The high side being too high tells you that you have an obstruction or are overcharged BUT the compressor needs to be running.

From #1 in the link below

Quote:

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Locate the vehicle's AC compressor for reference, and it's important to monitor what the AC clutch is doing. When the AC compressor is disengaged, only the outside of the pulley will turn. When it's engaged, the entire clutch assembly will turn, driving the compressor. Your compressor is designed to not engage at all when refrigerant pressures, or volume is too low.

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It also has the recommended pressure based on the outside temp.


AC recharge

The clutch could be bad but you won't know if it's not "kicking on" if the freon is low...

If you want to test that the compressor works, locate the low pressure switch, unplug it & jump with a paper clip. Make sure you ac controls are set to "on" &engine is running. When you jump the switch look & listen for the compressor to "click" on. You'll see the clutch engage if it's "functional". This will simply tell you if the compressor works. If it does then get some gauges & check your pressures. They along with the vacuum can be rented from O-O-OO'Reilly Auto Parts Ow(with credit card"deposit")! You may Google how to tear your low pressure switch. They sometimes go out after 20 years or so.