1994 Ford Taurus - AC & Heat Blowing Lukewarm

My 1994 Ford Taurus (156k miles) had been working great until recently when the AC & heat started blowing lukewarm/cold and the temperature gauge started leaning more to HOT than usual. My coolant level is fine, I have checked for leaks and there are no drips, and I just replaced my air filter.

Obviously, I am a kid just learning this stuff, but I would love a mini-lesson, if possible.

I would consider installing a new thermostat. If the old one is sticking or slow to operate it can cause the engine to run too hot or too cold. This is often the cause of poor heater performance. Thermostats are inexpensive, and replacing one is a good excuse to flush the cooling system and add fresh coolant.

You also want to be sure the cooling fans are working correctly. If you start the engine and let it idle, it will come up to operating temperature and the thermostat will open (assuming you have installed a new one). At this point the coolant in the radiator will start to warm up, and when it is hot the cooling fans should come on to cool the radiator.

If you let the engine run the fans should cycle on and off to maintain the correct temperature in the radiator. They should also come on whenever the AC is engaged.

Make sure those things are working correctly, then see how the heat works.

AC that doesn’t get cold usually has lost some refrigerant via a leak. This must be checked by an automotive AC shop.

Does the output temperature vary much? Is the AC cold when the car is started the first time for the day, and then goes warm as the engine heats up? If the answers are “no, yes”, then it might be an issue with the electric blend air door. This door determines how much (if any) of the air flow goes through the heater core. If it’s stuck, it could be your problem. It is moved by a little electric motor. This is true even if you have manual climate control.

I was about to suggest the blend actuator…

That’s one of the few things that could cause you to be getting lukewarm heating inside the passenger compartment while running hot. That or a plugged heater core.

I wonder about a waterpump, too - if you’re not pumping coolant well, you’ll run warmer than usual, and who knows if the computer will let the AC engage if it is sensing that you’re too hot…

Thank you for the suggestions.

I installed a new thermostat (the gasket was basically destroyed and there was a lot of gunk around it) and now the AC works perfectly, the heat is not working (still blowing lukewarm) and the temperature gauge is still on the hot side. The fan is cycling correctly, exactly as you described.

What might be my next move?

In the end, it was the waterpump. Swapped that out, changed a couple hoses and it’s golden - AC is cold, heat is hot, temp is right up the middle. Thank you for your help.

Correcting poor AC performance with the installation of a new thermostat raises questions.

Ordinarily I would just let someone believe that a new thermostat corrected their cars poor AC performance but since you say you a learning I will probe a little deeper.

What was the exact AC complaint? do you feel your engine was overheating (into the red) and this was causing poor AC performance? I would be more inclined to believe that the new thermostat cured your cars HEATING concern.