Diagnosing Car Heater Problems

by Bob DeP.


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Hey Bob!
I own a Chevrolet with a heater problem. When you turn the heater on you can hear the blower fan blowing (so we know that's working), and you can hear all the vacuums when you move the heater controls from "defrost" to "vent" to "blend" etc. But there's very little air coming out of any of the vents. When the heater is cranked up to high, you can barely feel the heat on your face! Please help me!
Demi

Demi.
I have been getting many questions and comments about cold driving this year. I suppose that it's the season. Here are a few things to look for, but pay close attention to the symptoms, because they all mean different problems.

1) There is no heat, the fan blows, the temperature gauge shows normal, and there is no noticeable air flow out the vents.

Most cars heating system uses a series of vacuum operated diverters. If there is a problem with their operation, the air flow may be dead ended or blowing out the wrong area. Some causes could be a bad vacuum line, or a broken diaphragm in one of the diverters. You'll need to get behind the dash to check individual lines.

2) I get air flow, but its cold.

Two possible problems here. One is that you are low on engine coolant. You see, the system is designed to reduce coolant flow to the cabin when coolant is low. This may seem bad to you, but it is protecting the engine. When you stop and the engine is cool, check the coolant level. If it's low refill with the proper coolant. The other possible problem is that the thermostat has failed in the open position. If that's the case your engine temperature guage should give a low reading. To fix it you'll need to replace the thermostat.

3) I get nothing, no fan, no blowing no nothing.

Well, this would seem like an electrical problem with the blower motor. Start with the fuse. If the fuse is good use a volt meter to see if there's electricity at the fan. If there is, it's probably a bad fan motor.

Now, these all pertain to vehicles without electronic climate control. Once you add a computer in between, there is a whole different set of things we need to do. And most times, its the computer that has faulted and needs to be replaced.
Good Luck!
Drive Safely!
Bob, The Auto Answer Man


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