Car Doctor Q&A: Where’s the Heat?

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Now that most of the country is in the depths of winter, heat issues are a constant question for AAA’s Car Doctor, John Paul. Sometimes heat problems can be expensive to fix. This one’s cheap and easy:

Q.I have a 2006 Jeep Wrangler unlimited, purchased new, with 153,000 miles on it. Now that it has gotten cold, I have been using the heater and noticed the heater would only blow air on the highest of the four settings on the switch. Should I replace the switch or is there something else, perhaps a relay or some electronic sensor?

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A. The most likely problem is a faulty blower motor resistor. The blower resistor controls the speed of the blower fan in conjunction with the fan switch. The fan works on the high setting because in most cases when the fan is switched to high, current bypasses the resistor.

This part can be checked with sample tools and if faulty is easily replaced. The cost of the resistor is as high as $35 and can be purchased for as little as $8 on-line. A good source for Jeep parts is Quadratec, which sells the part for $21.

There are only a couple of screws and shouldn’t take more than 15 minutes to replace. Here’s a five minute video showing you how to swap it out:

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.