94 Miata AC Running Hot, Majority of AC System Under 3 Years Old

Hi everyone,
For the past maybe 10 months, my car has been giving me new AC problems. The AC runs just fine when I’m driving normally or on the highway (basically without stopping for long periods of time and out of traffic). But when I stop for a long time (traffic, drive-thru, long light), my AC begins to run hot. To be more specific, the car actually begins to feel like it is running with more difficulty, as the engine starts running loudly and then I know that it is game over and it begins spitting out hot air. I generally just turn the AC off and put the windows down until I can get moving again, and then the AC is colder when I turn it back on.

Now, about 5-6 months ago I took it to my Mazda guy and he checked it out. Of course, it did not do what I wanted exactly, showing him what really happens when it sits for too long. Anyways, he said that everything seemed to be fine & both fans were working, but that the freon (r134) was low and he charged up the system and added some freon. After this, the AC was running MUCH cooler than it was before and the problem stopped.

That brings me to the last couple months; the problem has returned. This indicates to me, perhaps, that the freon has leaked out at this point, so it needs some more r134, but with dye, so that they can get a sniffer and pick the leak. Additionally, the engine is not overheating or anything of that sort, so I don’t think it has to do with the radiator or coolant. I have essentially replaced almost every other part of the AC system in the car within the last 3 years. I have replaced the condenser, one of the fans, the water pump, hoses, everything you could imagine that isn’t the compressor or the second fan.

Please help & thank you!

It sounds like there’s a small leak in the system that’s allowing the refrigerant level to get too low.

You can use the dye to locate a refrigerant leak, but a sniffer works better. A sniffer can locate a leak as small as 1/2 ounce per year.

Determine where the leak is located and then decide if it’s cost effective to fix the leak. If it’s found that the evaporator is leaking, I’ve used refrigerant with a stop-leak to repair those type of leaks.


A agree with Tester, you have a leak. My Mustang has a small leak, I usually have to add a can of R134a every two years or so. Right now it’s not worth fixing from a financial standpoint. But if the leak go to the point where I was having to add refrigerant every 2 months or something, then I would definitely have it repaired properly.

I’m with @tester. Add a can of R134 with stop leak. It’s cheap and will probably fix it for the foreseeable future.

I’ve had them put in refrigerant & charge up the system, but it went hot again. I’m wondering if the leak my be in the compressor? I need to double check because I think that’s the only part I haven’t replaced in the last 3 years.

If the compressor is leaking, you’ll see oil/dirt on the front of the compressor behind the pulley.


Hope this isn’t happening in your case, but there’s an insidious cycle that can develop with AC systems. Something breaks, and contaminates the system w/debris. That part is replaced, but the debris circles around and around and eventually breaks the part you just replaced, or something else. Etc etc. This can be compounded by overfilling the system with the coolant. It’s easy to think if a little bit is good, more is better. But it doesn’t work that way. Overfilling can damage an otherwise working system. The proper way to fill is to remove all the coolant into a temporary holding tank, then meter the exact amount back in. All the above is more of a problem in newer cars, in a 94 like yours hopefully this is happening. I think though you’d serve yourself better to visit an AC specialist.