How To

Ask a Mechanic.........Cold Passengers in a Ram Pickup

Today we’re discussing heater issues in a Ram pickup.

Every week, we answer your questions about what is going on with your vehicle. Today we’re discussing heater issues in a Ram pickup.

Dear Ask a Mechanic,

Now that the weather has turned cool again, my wife has noticed that the air coming from the vents on the right side of the heater in my 2011 Ram 2500 isn’t nearly as warm as it is on my side. It seemed to work fine last year. What could cause this? – Chilly Spouse

There are two primary reasons why the air on the passenger side could be appreciably cooler than that on the driver’s side (or vice versa).

In dual-zone systems, the internal ducting is split, with each side having its own “blend door” that directs air either through or around the heater core to control the temperature. A failed blend door actuator or a broken blend door can allow air to bypass the heater core, reducing how much warmth it picks up. You may be able to diagnose this yourself. With the mode set to dash vents and all the vents open, try switching the temperature on one side at a time from full hot to full cold with the fan on high speed. There should be an audible change in the sound and a slight difference in the amount of airflow on each side as the door moves (the changes are due to the added restriction of the air blowing through the heater core).

If the sound and/or airflow didn’t change, try doing the same test with the fan at minimum speed. You may be able to hear the blend door actuator operating (it’s a tiny electric motor with gears inside). A moving actuator with no change in airflow suggests a failed actuator gear or broken blend door. Replacing a broken door typically requires removal and disassembly of the entire system.

If the airflow in the heater appears to be getting controlled properly, or your vehicle has a single-zone system, a possible cause is a blocked or restricted heater core. The core is like a miniature radiator, with lots of tiny coolant passages that can get blocked by sediment from old antifreeze, or corroded material from elsewhere in the cooling system. Because of the orientation of the core inside the heater box, one side’s airflow often passes through the portion that’s more plugged up (and therefore less hot). We’ve seen this numerous times in Chrysler models, but it is certainly not unique to them. Flushing seldom seems to work, and core replacement is the fix. Unfortunately, in many vehicles – including your Ram, this is a major repair, necessitating removal of the entire instrument panel to complete.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.


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