Any way to check Compressor without Charging System?

[ericdude]

IIRC, there's a safety mechanism that stops the clutch from engaging if the pressure in the
system is too low. Is there any way to check whether the compressor is good without
charging the system with Freon? If I charge it and find the compressor is bad, I'll have to
dump the charge and recharge it.

[SCT]

Unless you have those fancy A/C Recharge machines, then you don't lose anything... I don't think there's a way to bench test a compressor. If it makes sounds, change it.

[kathyricks]

You first need to determine if the system is partially or fully discharged of refrigerant.
Unscrew the black cap from one of the schraeder valves (tire like valve) that is attached to the low pressure "S" metal refrigerant line ("S" = suction). Slowly depress the valve using the eraser side of a pencil and listen for a hissing noise similar to when you depress a tire valve. A hissing noise is a good sign the system is partially charged and just needs to be topped off with refrigerant to restore system pressure and compressor operation.
Adding only 1 can should enable the compressor magnetic clutch to activate and run the compressor.

If you find the system is totally discharged (no hissing sound from the schraeder valve) then the system has a serious refrigerant leak that must be found and repaired before you can recharge the system and check for compressor operation.

.

[freakinbox]

usually with something this old you will need a new a/c condenser. But it also depends how long a small leak has been left untouched. In a lot of cases the kit you can use to fill it up will seal things such as that and the system will work fine. So just because the system is completely drained doesn't mean there is a large leak, just like a tire with a small leak will go flat eventually.

[kathyricks]

The AC condenser is made of metal and can last 50 years or 500,000+ miles (except in a rust belt State like western New York).

Refrigerant leaks usually come from the compressor shaft seal and are caused by the owner neglecting to run the AC system occassionally during the winter months.

The Toyota AC Technician training manual strongly advises against adding additives to the system to seal leaks.

[retiredat44]

Originally Posted by ericdude

IIRC, there's a safety mechanism that stops the clutch from engaging if the pressure in the
system is too low. Is there any way to check whether the compressor is good without
charging the system with Freon? If I charge it and find the compressor is bad, I'll have to
dump the charge and recharge it.

there needs to be a charge in the compressor to check it... whether you do it or a shop.. as long as it is R134a, it's not expensive.. but if you use the old R12, it's very expensive..

if you want to do a leak check, it can always be filled with 1 can only, that should be enough to run it and check for a major leak, but maybe not a small leak under high pressure. a case of R134a refigerant from Sams or Costco is less than $40.00.

also, there is no way of telling how much oil is in a system that has no refrigerant in it.. as the oil leaks out with the refrigerant... and the only way to check the amount of oil in a system that is empty and the parts repkaced is to take the compressor off and fill it with the proper type and amount. Of course you can guess.... but... you might be wrong..

[kathyricks]

Most refrigerant leaks are small seepage leaks and so the gas escapes but not the oil.

A can of R12 is only $25 on ebay in the summer and $15 in the winter and system capacity is only
two 14 ounce cans so the cost is not a big deal. Only 1 can is needed to test if the compressor is still good.

[retiredat44]

you can fill it with compressed air... but then you would not only be filling it with moisture which is a huge NO-NO! But it would also not be able to use halygen (sp?) leak detectors..

The oil inside would defintely need to be drained out the filter/drier changed, com[pressor taken off to drain the oil, and refill,, al the seals you open would need replaced too.