Every week, we answer your questions about what’s going on with your vehicle. Today we are discussing the 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 out of the air vents on the right side of the radiator on my 2011 Ram 2500 is not as hot as the one on my side. It seemed to be working well last year. What could be causing this? – Chilly Husband

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

In two-zone systems, the internal ducts are split, with each side having its own “mixing door” that directs air through or around the heater core to control temperature. A faulty mix gate actuator or broken mix gate can allow air to bypass the heater core, reducing the amount of heat it picks up. You may be able to diagnose this on your own. With the mode set to dash vents and all vents open, try changing the temperature one side at a time from hot to 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 to each side as the door moves (the changes are due to the additional restriction of the air blown through the heater core ).

If the sound and / or airflow has not changed, try doing the same test with the fan at minimum speed. You may be able to hear the mixing gate actuator working (it’s a small electric motor with gears inside). A moving actuator without a change in air flow suggests a faulty actuator gear or a broken mixing door. Replacing a broken door usually requires removing and disassembling the entire system.

If the airflow through the radiator appears to be properly controlled, or if your vehicle has a single zone system, a possible cause is a stuck or restricted heater radiator. The core is like a miniature radiator, with many tiny coolant passages that can be blocked by sediment from old antifreeze or corroded material from elsewhere in the cooling system. Due to the orientation of the core inside the heater box, the airflow to one side often goes through the most plugged (and therefore less hot) part. We’ve seen it a few times in Chrysler models, but it’s certainly not unique to them. Flushing rarely seems to work, and core replacement is the solution. Unfortunately, in many vehicles, including your Ram, this is a major repair requiring the removal of the entire dashboard.

Ask a Mechanic is written by Brian Early, a Certified Red Seal Automotive Technician. You can send your questions to [email protected]. These answers are for informational purposes only. Please consult a certified mechanic before performing any work on your vehicle.