HVAC Actuator Problems?

[Niveko]

My heat is stuck on defrost only. The fan's speeds all work fine. The re-circulation door (which is located behind the glovebox) will not close and cycles a dozen or so times before stopping when the truck is started and produces a very audible knocking noise.. It also does this when the truck is shut off. Any insight as to what is going on is highly appreciated. Also, I am getting lots of frost build-up on the inside of my windshield and driver/passenger windows.

Thanks
K.O.

 

[MADDOG]

It's either the actuator (but it sounds like it's working) or the mechanical portion of the blend door. Pretty common failure many owners have to deal with.

If you want to tackle the repair job yourself I'd recommend getting a service manual. Otherwise, any good shop can fix it for you but it does take quite a bit of labor to get to that damned thing buried up and under the dash.

 

[Niveko]

It's either the actuator (but it sounds like it's working) or the mechanical portion of the blend door. Pretty common failure many owners have to deal with.

If you want to tackle the repair job yourself I'd recommend getting a service manual. Otherwise, any good shop can fix it for you but it does take quite a bit of labor to get to that damned thing buried up and under the dash.

So there are two separate mechanical components to the re-circulation door, one being the actuator, and one being something else? What controls the re-circulation door from closing and opening, is it the actuator, or something else? I am capable of doing the job myself, just trying to narrow down the culprit is the issue. Thanks for the help.

 

[Gary2]

Funny how Dodge /Ram has had problems with the doors in the HVAC housing since the 90s and they still have not mastered it .

 

[MADDOG]

There is an actuator (what you hear moving around behind the dash) and the blend door, a baffle that moves as the actuator directs based on the control setting on the dash.

 

[Jeepwalker]

Well, let's see ....sounds like you have multiple things going on.

Let's start with the 'knocking' sound: chances are very good that one of the actuators has a cracked gear/shaft. The female portion of the drive motor has a nylon gear that fits over a square drive (door shaft). This long, female portion that rotates the door shaft commonly cracks (lengthwise) and then opens when the door reaches it's end-travel (at the most torque) and then 'skips' instead of stopping the motor. The motor keeps skipping on the shaft because there isn't enough resistance to stop it. The quick fix is to buy at least one new motor and replace it. You can ID which one it is by feeling it and you'll feel it click as it skips. If its the defrost it should be easy to get to as far as I remember. Just google a drawing of the HVAC box. All the actuators should be the same. Ebay is a cheap place to get one. Hopefully your truck doesn't have automatic (dual) temperature control. Even if it does, with luck, the motor in the back of the HVAC box isn't the problem.

As for the outside air/recirc air blend door, if it's like the HVAC boxes I've looked at, what I would do is take a strong flashlight and look 'up' from the passenger's side footwell. It's an awkward position, but on the ones I've dug into, I was able to look up through the grate to see what's going on with the blend door. It wouldn't be uncommon if the door is separating at the hinge. The hinge may not be a true hinge, more like thin piece of the plastic door which flexes open/close until after enough cycles the plastic breaks half-way. Then the door hangs down and to the side and neither opens or closes all the way. The motor will cycle until it tears the hinge the rest of the way (then the door will drop down). The quick fix I've done is to take a piece of stiff wire the right length with sharp ends (sharp like a finishing nail) and wedge the wire in there to hold the door shut until you can get at it. The actuator could be bad too. You won't have outside air, but you'll also have good heat again until you get at it (or just leave it).

Good luck.

 

[Niveko]

Well, let's see ....sounds like you have multiple things going on.

Let's start with the 'knocking' sound: chances are very good that one of the actuators has a cracked gear/shaft. The female portion of the drive motor has a nylon gear that fits over a square drive (door shaft). This long, female portion that rotates the door shaft commonly cracks (lengthwise) and then opens when the door reaches it's end-travel (at the most torque) and then 'skips' instead of stopping the motor. The motor keeps skipping on the shaft because there isn't enough resistance to stop it. The quick fix is to buy at least one new motor and replace it. You can ID which one it is by feeling it and you'll feel it click as it skips. If its the defrost it should be easy to get to as far as I remember. Just google a drawing of the HVAC box. All the actuators should be the same. Ebay is a cheap place to get one. Hopefully your truck doesn't have automatic (dual) temperature control. Even if it does, with luck, the motor in the back of the HVAC box isn't the problem.

As for the outside air/recirc air blend door, if it's like the HVAC boxes I've looked at, what I would do is take a strong flashlight and look 'up' from the passenger's side footwell. It's an awkward position, but on the ones I've dug into, I was able to look up through the grate to see what's going on with the blend door. It wouldn't be uncommon if the door is separating at the hinge. The hinge may not be a true hinge, more like thin piece of the plastic door which flexes open/close until after enough cycles the plastic breaks half-way. Then the door hangs down and to the side and neither opens or closes all the way. The motor will cycle until it tears the hinge the rest of the way (then the door will drop down). The quick fix I've done is to take a piece of stiff wire the right length with sharp ends (sharp like a finishing nail) and wedge the wire in there to hold the door shut until you can get at it. The actuator could be bad too. You won't have outside air, but you'll also have good heat again until you get at it (or just leave it).

Good luck.

Did Dodge change the design of their re-circ door from gen 3 to gen 4? I appreciate the information.

EDIT: I should mention that the knocking is in the same area where the re-circ door is failing to close/open; that being said, presumably the re-circ actuator is the culprit for both of the issues: the noise and the door not closing and opening properly. Is there any easy method of removing and replacing that actuator, as by the looks of things it is tucked pretty far underneath the dash.