ac runs and so does heat at same time no ac in car

Asked by Jul 24, 2016 at 11:19 AM about the 1998 Mercury Grand Marquis 4 Dr GS Sedan

Question type: Maintenance & Repair

ac runs and heater will not shut off

3 Answers

24,405

The heater core never shuts off. Even on the blazing hottest day it sits there in your dash, a little radiator dispensing heat. All that happens when you switch the temperature knob from heat to cold a little plastic door (called a blend door) swings over to direct air flow from the blower motor to go over the AC evap coil instead of the heater core. If you have good AC and COLD air (check the compressor is running) and HOT at the same time, it's a sign your blend door is stuck open to the heater core. Usually it's the blend door actuator that failed. The part costs about $35. The labor, however, to get to the heater cores plenum box is expensive. You either have to remove or loosen the dash, pull radio, passenger air bag, drop glove box, to gain access to it.

2 of 2 people found this helpful.

KenF How much does the labor to repair the blend door?

24,405

Blend door repairs are expensive due to the labor to access that area of the dash. About 4 hours shop time or more, the dealership will charge over 1,000 for this. The blend door actuator (typically the part that fails) costs under 40 bucks. If you can find a good guide online, it can be a good DIY job even for a novice. Try Crownvic.net, they have several posts there on doing a blend door or actuator replacement. The trick they use is to loosen the dash, wedging the passenger side up on a small block of wood and reaching in through the air bag opening to get to the actuator. I've done several CVPIs this way, and have it down to about 45 min-1 hour. Be sure to TEST the actuator too, before swapping it out. If you prefer to have a shop do it, just call local mechanics and shops, especially those that specialize in AC repairs, these types of places tend to have much better pricing that dealerships and chain shops.

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