A/C compressor won't shut off

Contactor relay.

Replace the contactor, wash the condenser coil. It's likely dirty, causing unsually high amperage draw, heating the contractor contacts and 'welding' them together. Also, replace the air filter to limit long run times.

I would agree with changing the contactor but a high head would not cause the contacts to burn and pit.

I would think worn out contacts and check your hard start cap. to see if you spot any damage. If so replace the relay and cap.

I also agree that you should wash your coils and change your air filter.

:-)

Nobody's going to check the compressor terminals?

I just had too... LOL

Your right.

But some times I worry about a home owner, who is just trying to save some money, get hurt while working on their own system.

Heck I have seen service tech forget what they are doing and have gotten hurt.

I've seen it too. If the OP does in fact try to do a self repair, I hope he knows enough about 220v systems to prevent a trip to the coroner's office.

Very true, I wouldn't advice a homeowner to check them either.

I was just being ornery. :-)

Thanks very much for the responses. I ended up replacing the contactor, and so far it's working fine. The old contacts were badly pitted.

And I even remembered to pull the fuse block out before I did the replacement, So no ambulance or coffin was required. No OP's were harmed in the making of this repair. :-)

I have a feeling I do need to replace the entire condenser unit, and probadly should do so before this one fails. I couldn't help but notice in my records that when this one was installed in 1985, they charged me $650 installed. I suspect it would be somewhat more today for a 42k btu unit.

Could they still use freon 22 in a new unit?

Some manufacture's are planning to stop production of their R-22 units at the end of this year.

Freon is a brand name. Like Isotron, Genetron, or Forane.

Refrigerants are known by number. There are numbers 11, 12, 22,

Which refrigerant do you want?

I want a R11 residential unit.

You going to s*it me one?

Yes but the new units with 22 is getting harder to come by and if you can find one don't worry about getting refrigerant