uarkman

i have a '66 mustang 289 with factory air conditioning that's fully charged with r12 coolant. if i try to run the a/c, within minutes the motor is overheating and the temperature gauge is almost maxed out. any other time it runs in the normal temperature range. anyone have any idea what could be causing this?

Scott H.

Loose belt?
Insufficient cooling capacity?
Plugged fins?
Just a few guess' off the top of my head.

Brandontyler65

new thermostat needed

ChaseFuller

I would say its a loose belt.But if i were you i would check out your AC clutch i can almost guarantee its about to go out my truck had the exact same problem and after about a month of driving with it like that my AC clutch broke.I am pretty sure its your AC clutch.

Chase.

Cannonball888

How would a loose AC belt cause his engine to overheat?

I think you need to upgrade your cooling system. 65-66 stock cooling systems are barely adequate in the first place. An A/C really pushes it over the edge.

grruminator78

sounds like a good excuse to upgrade to a new sanden with the new era refrigerant

DGA

Question -- Does it boil over? If not and you switch A/C off does the gauge ready correct itself quickly?

If it does boil over step one would be as suggested check the belt tension.


Driving with A/C on should not overload the cooling system. Idling may.

MC

I had a similar problem with my 66 with no ac. when i first got it I started messing with the heater switches and it started overheating, i flushed the radiator and replaced the thermo. now it runs fine.

Soaring

If your compressor is the old York, it is about to go south. I bet the compressor runs rough when you turn it on. If not the clutch, then the piston internally is about to freeze up causing undue pull on your engine. Don't use it any more until you replace it with a new Sanden. Then, of course, you will have the 134A frigerant.