I have an 81 Lebaron that I've been driving in the Michigan winter, and today on the way to work I noticed two things- my heat never really got hot, and there was no difference between hitting HEAT and DEFROST. Even on the highest setting, it was blowing out lukewarm air. There's usually a noticable difference between heat and defrost. It was working fine up until this morning. Could this be a vacuum issue?

Could be:

(1) clogged heater core

(2) blown vacuum pod on the blend door

(3) deteriorated foam weatherstripping inside the HVAC system.


Cures:

(1) flush the heater core. Replace if necessary.

(2) get a hand held vacuum pulp and test the vacuum pod. You should note that this problem might also be due to a faulty control head in the dash. These are known to disintegrate after several decades of use.

(3) disassemble HVAC system and replace weatherstrip with the stick on foam variety you can purchase at the hardware store.

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks for the information. I'm at work right now, but I'll start with what you suggested there when I'm home.

The sudden onset of the loss of heat suggests something is wrong with the vacuum pod or the control head. With a clog or degrading weatherstrip, you would have a gradual loss of heat as the heater core clogged or as more cold air bypassed the core.

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Casually looking for a Clifford hyperpak intake for cheap.

Did the engine reach operating temp.? (thermostat stuck open?)
Some vehicles have a heater water control valve, check to see if that is functioning correctly. (control valve stuck closed?)
DD

The engine reached normal operating temp, and is running decently, save for an intermittent stumble that has to be a fuel issue. That's for another thread, but I need to do some more board searching before starting that. I believe I do have a heater water control valve. I haven't ever touched it, so it should still be open, but I'll take a look.

Reed, I was doing some googling, but where exaclty is the blend door? And am I correct in thinking that the vacuum pod opens and closes the door, letting in cold/hot air?

First, Doc is right. A/C equipped cars had a water flow shutoff valve that stopped coolant flow through the heater core when the temp was moved to "cold." Check that that hasn't stuck closed or partially closed. It will be in one of the heater lines going to the firewall and will have a vacuum hose going to it.

Second, the blend door is just a common name for the door in the HVAC system that diverts air either past the heater core (cold) or through the heater core (hot). It "blends" the air, so it gets called a "blend door." You need to get a factory service manual for your year and model of car to really see how your system is put together.

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Casually looking for a Clifford hyperpak intake for cheap.

Okay thanks! I suppose I'll be back with more questions once I start getting into it.

Guys, I think it was the control valve under the hood. It was stuck closed. I sprayed it down with WD-40, and it seems to have loosened it a little bit. I'll probably just pick up a new one soon.