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No Heat

The heat on my 2002 Mercury Sable stopped working. Are there any suggestions for where to start first? I’m going to need to get it fixed soon, as Fall will soon be here.

Exactly what does it do or not do when you try to turn it on?

First check the coolant level in the radiator. It should be completely full.

Next, determine whether or not the engine is getting up to normal temperature. A stuck thermostat could be causing the engine to run too cool and that will result in little or no heat. It also uses more gas.

Then determine whether or not hot engine coolant is getting to the heater core. You can do this be feeling the heater hoses after the engine is warmed up. The heater hoses should both be hot.

If all that is OK the problem is inside the HVAC system. A stuck or inoperable blend door may be allowing incoming air to bypass the heater core.

Does the AC still work?

Be certain that you have sufficient coolant in the radiator. If you need to add coolant to get the heating system to work, check for a leak. If the coolant level is fine, the next suspect is the thermostat failing to close. Does your temperature guage read in the normal range? If not, it’s almost certain that your thermostat needs to be replaced. Do this right away, as a side benefit of an engine operating at normal temperature is that it gets better mileage.

Other problems could be something in the controls or a plugged heater core. The cars my Dad owned in the 1930’s and 1940’s had a valve under the hood that he would close in the summer so that coolant wouldn’t flow through the heater and open in the winter to get heat. The controls for coolant flow through the heater core do the same thing on your 2002 Mercury. If the valve that controls coolant flow to the heater core isn’t opening, you won’t get heat.

I don’t think the 02 Tarus/Sable uses a coolant control valve. I think it only has an electric blend air door.

You are probably right. There would have to be a complicated way to do something simple.