HVAC issue: Blend door stuck on Hot

I need some advice on an HVAC issue with a 1999 Mercury Sable. It’s an LS so it has a climate control system (you set a temp rather than just a cold/hot knob)

I was driving on a nice warm day with the AC on, and all of a sudden it changed to full-hot and will not change back to AC.

I got home and tinkered, and found out the blend door is stuck on hot air. I took out the blend door actuator so now I can flip it back and forth manually (at least I got to have sweet cold air back!)

So I isolated the problem to the blend door actuator stuck on Hot. I got a replacement from Amazon, but this one does not respond to any temp. setting adjustment.(I knew that could happen)

I assume at this point that the problem is in the component that controls the blend door act. either the whole climate control module or its thermostat. Is that a reasonable assumption?
In other words, what should be my next step? Can you service those units, and are there any flaws in my previous diagnostic steps?
Thanks in advance,

It’s probably the actuator has failed , a sort of electrical motor gadget. In any event you’re going to need to take a look-see at the actuator, mechanical linkage, and it’s electrical connector It appears the expected labor fee is about an hour to replace the actuator (by an expert mechanic) so likely driveway diy’er possible in 4 hours or so. Obtain the repair instructions and take a look at the procedure for yourself before deciding. One thing you have in your favor, since cold weather is ages away (presuming you live in the northern hemisphere), you got plenty of time.

It sounds like the HVAC module isn’t driving the actuator.



I would look online and see if there’s a reset procedure that could be done either by disconnecting the battery or with a scan tool. Someone here might know that. I’m a lot more familiar with GM’s stuff. If a reset isn’t possible or doesn’t help, it sounds like you’re on the right track with the other options. Is the thermostat for the control module replaceable separately and pretty cheap? If not, it might pay to have someone hook a scanner to it and diagnose it before spending too much on parts.


Good idea above, sometimes the actuators lose track of their home position. Requires an appropriate scan tool to know if this is the problem.

Got it!

So I followed the reset idea, I found out the reset procedure, it returned codes 24, 25 and 125. I did a reset, and the blend door motor is turning again!

I’ll try to look into these codes to see if there are issues I need to address.

Thank you all for the help!


Awesome! I hope it keeps working.

Just to add a bit about the EATC units. They use vacuum and mine was different with some foam pads and a bit more complex. The link does not show this one as so.
With time the foam can rot of course and O-rings harden and cause problems. The option is to get a rebuilt unit (on eBay, etc) or perform a DIY repair. I’ve done the latter. The link shows easy; mine not quite so much.

A few other trouble areas. The one-way valve (front of firewall) or leaks in any of the in dash vacuum pods can also cause problems depending upon settings.
One note. It was discovered many years ago that there may be too much travel in the blend door motor. That can lead to door arm stopping and the motor not; which means breakage. The solution would be to never set the temp on the Min 60 or Max 90. Stay a degree or two above or below. Affect is nil.

Hello everyone,

So I am back… and I still have some problems.

Now that the actuator is moving again, I tried to install it, and while doing so I noticed that the blend door does not move right. There seem to be a stubborn bind while trying to flip it back and forth. I didn’t notice it before. I suspect that this bind is why my motor got stuck and gave an error,

Are there any other blend doors that might be in the way? or what could be the cause of this? right now the only way I can see forward is either taking the entire dash out and trying to cut openings into the ductwork to see whats going on. I do have a boreoscope, so I might try an exploratory hole.

Any other less invasive ideas will be greatly apprictated at this point… :slight_smile:

You might need the blend door repair kit

it’s specifically for 1999 Sables with automatic temperature control

The Dorman part # is 902-223


One idea, you could try to get a shop-vac nozzle into that area, maybe there are bits of twigs and leaves interfering with the door’s movements. Going forward good idea to thoroughly vacuum the inlet-air area right under the windshield (exterior) every once in a while to minimize the amount of debris that gets sucked into the HVAC duct work. I do that w/every oil & filter change.