Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

A/C Not Working When Truck is Stationary

Have a question regarding my A/C unit not working. I have a 2005 Dodge Ram 1500. My AC only works when my car is moving and my foot is on the accelerator. When I stay stationary, or stop at red lights, the AC blows out hot air. When I go on the expressway and am moving with my foot on the gas, it blows out ice cold air.

Looking forward to some advice. Thanks.


Internet Private Investigator

Sounds like it may be low on R134a refrigerant.

The first thing to check is if there’s a lot of debris on the front of the condenser. Things like bugs and leaves. The condenser is like a radiator where it removes heat from the refrigerant so it can converted from a high pressure gas into a high pressure liquid. If the condenser is restricted with debris, not enough air passes thru it when stopped to convert the refrigerant into a liquid so the air turns warm. When the vehicle is moving again, enough air is being forced thru the condenser so the refrigerant turns into a liquid again and the air gets cold.

If the condenser doesn’t appear to be restricted with debris, then the next thing to do is have a set of manifold gauges connected to the system to check it’s state of charge of refrigerant.


Is the engine cooling fan attached to the engine or is it electrical? If it’s electrically driven, it must be working any time the A/C is on…

This symptom suggests that there is air passing through the condenser when the vehicle is moving but not when the vehicle is stopped.

Does this vehicle have an electric fan? If it does, make sure it kicks on when the A/C is on. If it does not kick on, check the fuse/relay for the fan.

If the vehicle has no electric fan, check to make sure the mechanical fan is pulling air when the engine is warm. The fan clutch should free-wheel when the engine is cold, and get stiffer and stiffer (pulling the fan harder) the hotter the engine gets. You will, of course, shut off the engine before feeling the fan for rotational resistance!!!

If it’s not a low refrigerant problem then it might be a blend door issue. The blend door is what keeps the heater core out of the airflow when the A/C is operative and a quiok look shows that blend doors have been a problem on these vehicles.

Whether or not this blend door is vacuum operated I have no idea but a vacuum problem could cause this if the door does use this method of control.

With the A/C on and the truck idling raise the hood and inspect the accumulator. If the refrigerant level is as it should be then the accumulator should be cold and sweating at an idle and there should be a condensation drip underneath the truck.