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93 Lincoln Town Car rrr thump thump heat problem

My brother’s 93 Lincoln Town Car makes a noise under the dash board that sounds like rrrrrr thump-thump rrrrrr thump-thump. This problem is related to getting heat in the car. If outside temperature is 45-50F he gets heat, when colder than 45-50 he gets no heat just rrrr thump-thump. He said the blower is running all the time under these conditions so no problem with blower. This vehicle has 4.6 v8, auto transmissionand auto climate control.

check coolant level, 7 out of 10 cars that I check for no heat are low on coolant

Sounds like the air-blend door is getting stuck when the interior temperature is low. The thumping sound you hear is the electric motor trying to get the door unstuck. They [dealer] had to replace the whole door/air duct assembly on mine while it was still under warranty. (For exactly the same issue, no heat when it was cold inside the car, but heated okay if warm inside car.) If you can get to the blend door, you can probably find a less drastic solution. You probably just need to shave some plastic off somewhere.

This is one of the other 3 out of 10 cases.

The only problem with that explanation is that it does not account for heat above 45-50 and none below that. I am puzzled by that aspect. It makes me suspect an EATC (auto control) problem. It might pay to put it into the self test mode and check for errors. If no one here knows what buttons to push to do that, post your question at

Yes it does. This was the case with me too. Below 45 or so (inside the car), the plastic of the air chamber warps and contacts the blend air door and keeps it from moving very much at all. Trust me on this. There were several trips to the dealer and I finally figured it out by watching the door when the interior was cold. They replaced that assembly, and the problem stopped. I had the thumping sound of the air door too, that’s a big part of what clued me into it being the problem. Haven’t you ever had house doors that stuck in some weather conditions, but worked perfectly well in others? Run the self test on the climate control when the door is stuck (when it won’t heat) and I promise you will get a code for stuck blend-air door.

I see. thanks for the insight.

I have been negligent in coming back to look at the replies posted here. I think tardis and beadsandbeads have nailed this one. I logged in today and was very happy to see any reply at all. I called my brother to pass this along and he was not there. I should be speaking with him soon though. I really do appreciate your answers. I will post the outcome when it gets fixed. Thank you both again for helping with this.