A/C stops working on the highway



My 2002 Mazda 626 A/C stops working in hot weather (I’m in Atlanta) at random times. Just yesterday, after having a shop do diagnostics and put more coolant in (was down40%), I ran on the highway for 10 minutes, very cold, then it stopped. Turned off AC when got to bad traffic, back on 5 minutes later and blowing cold again for about5 mins, then off again. The engine temp is fine, and both radiator fans were still running. The shop wanted to replace the idle control valve because it was causing the engine to start stalling at idle (AC cuts off then too). Don’t think that has anything to do with it failing on the highway though. Any suggestions?



Where did 40% of the refrigerant go? If the shop did not fix the leak, but merely recharged the system, then I’d say it is still leaking, and as the refrigerant level drops it can do exactly what you describe.

Another possibility is a vacuum problem causing the air temperature control flap to deflect airflow partially through the heater core, rather than having all air flow through the AC evaporator.


It sounds like the evaporator may be freezing up. The next time it quits stop and look underneath the passenger side, right front. You should see a water condensation drip.

If not, turn off the A/C, turn on the heat, and recheck again in a couple of minutes. If water is streaming out the evap. is freezing.

This could be caused by an improper refrigerant charge, faulty expansion valve, etc.


And don’t forget a dirty evaporator coil or dirty (HVAC) air filter.
Since 40% of the charge leaked out, there must be a leak somewhere. Add some A/C leak finder dye (must be compatible with polyol ester oil for R134a). Then use a blacklight to find the leak and then fix the leak.


Your car, or any other, does not even HAVE a HVAC air filter so ignore that irrelevant comment.