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2002 mercury mountaineer heater

In my suv there is a heater in the front and the back, they are separate controls for each. The heater in the front works when the engine is at about 2000 rpm’s. The heater in the back does not work at all. All it does is blow cold air in the back. This is 2 questions in one topic i know, but to me they seem to be coming from the same place. Any suggestions?

I would start with a check of the engine cooling system. Make sure the coolant is clean and full. Check for any leaks. It sounds like you might have air in the system that needs to be bleed out. If so, you have a leak somewhere that let the air get in, unless you had recent service and they didn’t bleed it correctly.
What does your engine temperature gauge indicate. If it stays low, you may have a bad thermostat.

You should have heat at any engine speed. Is the engine reaching normal operating temperature?

Check the radiator and make sure the cooling system is full, then check the owner’s manual for any special procedure to bleed air pockets out of the system. There may be a special air bleed valve somewhere. If there is air in the system it will not work correctly.

Does the rear unit have heat and AC, or is it just a heater?

The rear compartment has separate heat and air. The engine is reaching normal temperature and not going above or below. I have watched that to make sure the engine has not been over heating. When I get home today I will check the owners manual to see about bleeding the air.

As with the main heater/ac under the dash, there are motors that operate the blend doors on the rear unit too. They are electric so several tests need to be run. Is it a switch problem or blend door motor problem and if you have ATC it gets more complicated. To start with, feel the hoses under the right rear corner of the truck to see if they’re getting hot from water flow.

I think that the odds that both blend doors (in both systems) failed at the same time are less than then odds that a single failure point (such as air in the cooling system) is responsible.

I have checked the water level and noticed a small leak. It is so small I can’t find where it is coming from. I am unsure where the coolant system having air in it would cause the heater to only work when the engine is being reved up. I am checking that now though. And as far as the rear heater goes I do not know where to start with checking it. As far as the hoses go, they are warm when the car is warmed up.

Air in the system can block the flow of water to the right places.

This definitely sound like an air pocket problem. There may be a bleed valve for the rear heater core.