Tempurature control not activating blend door?

CORY2427

MEMBER
1998 MERCURY GRAND MARQUIS
4.6L
V8
2WD
AUTOMATIC
128,000 MILES

Just recently put heater core and a new blend door actuator in but noticed at the heat control that when I move dial from red (heat) to cold (blue) that actuator is not moving bled door closed or open. Figured most likely the heater control module maybe doesn’t know what fuse would control it but have not seen none blown. Everything else works on module. I did have a problem while back not wanting to change where it blows but other than that stuck on what to do.

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
48,581 POSTS

I would remove the temperature blend door actuator to move the pivot by hand to make sure it is not bound up. With the actuator off of the HVAC plenum but still plugged in, move the controls to see if you can get movement. You may have a defective part, here is the location of the unit so we can be on the same page, there is no fuse for this, just for the HVAC system which the rest seems to be working? Also, make sure the little vacuum lines under the hood going to the HVAC system are intact. Check out the images (below). Let us know how it goes.

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Tuesday, December 31st, 2024 AT 5:51 PM

CORY2427

MEMBER
291 POSTS

All vacuum lines are good heater core is brand new actuator is fine I’ve checked the old one to it was fine by taking them apart and using a battery on the motor watching it turn all controls work when switching from floor to defrost to mix and anything else it’s just not telling the actuator to close the door when you mess with the temp to move from heat to ac so if there is no fuse for it then it would be in the climate control piece I guess only option I can think of unless you got any.

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Tuesday, December 31st, 2024 AT 6:28 PM

KEN L

MASTER CERTIFIED MECHANIC
48,581 POSTS

If the system worked before I would say the control board inside the actuator is bad, the motor can still work but the actuator could still be bad, or the HVAC controller is not working. Can you work the blend door pivot by had, does it move freely?

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Wednesday, January 1st, 2025 AT 10:36 AM

CORY2427

MEMBER
291 POSTS

Yes, open close like it should actuator don’t think it worked before so changed from what I seen them controller are bad to go down on vacuum side of things, but the problem I having it’s just like it is not getting to command to open and close the door might have to change controller and see what it does. I’ve gone over everything nothing else to really do but change that out since there is no relay or fuse for it.

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Wednesday, January 1st, 2025 AT 10:58 AM

KEN L