No power to blend door actuator?

[armstrong486]

Hey guys, I have a ‘99 Ram 2500. The blend door actuator that makes the blend door go from hot to cold and cold to hot isn’t working. I know they’re notorious for the plastic tips breaking off and rendering it useless, a common fix is replacing it with a metal tip.

1. So I pull it off ready to replace the plastic top...previous owner did this already, it already has the upgraded metal tip
2. I replaced the blower motor 40amp fuse and Relay under the hood, and 10amp fuse in the cab
3. I replaced the blower motor and blower motor resistor (figured it was unrelated but wouldn’t hurt as they Harry worked anyway)
4. I got a brand new OEM blend door actuator
5. After none of this worked, I ripped apart the dash and installed a new HVAC control panel with a new temperature switch

After all this I still have no power to the blend door actuator. I’ll plug it in, turn the temp gauge and the rotating piece on the actuator does absolutely nothing. I have it fully removed at the moment so I can rotate the blend door by hand as needed, but this is getting very old and I’m trying to fix it properly. Any ideas?

 

[DavidC]

You are turning the ignition to run correct ?. I just went through this.
Use the 2000 wiring diagram as the 99 is incorrect.
https://www.turbodieselregister.com/threads/99-blend-door-wiring-diagram.268158/

Maybe some help
https://www.turbodieselregister.com/threads/99-blend-door-and-coupler.268170/
I had read the wiring connector can also cause problems, I think it's the one at the motor, break out the voltmeter and start checking as I believe you will have all the info needed.

 

[armstrong486]

Thanks David. So that second link you posted was for the “heater treater” to replace the flimsy plastic tip with a metal one. I attempted to do that, but the previous owner already did that. As far as the first link, I think the 2000 wiring diagram is correct for the 1999 (it’s funny because the guy in the 2nd link said the same thing, FSM for 1999 incorrectly lists the blend door as vacuum actuated, it’s actually electronic).
That being said, based off the 2000 wiring diagram, what would I need to replace to fix power to the blend door actuator? I’m terrible at reading diagrams like that

 

[DavidC]

First, turn key to run, check 10amp fuse 2 to ground. Should have 12vdc on both sides.
Second with key in run check the dark blue at blend door motor to ground then dark blue to black, light green tracer and verify 12vdc on both tests.
Third test yellow with orange tracer to ground and yellow orange to black light green. Adjust temp setting and voltage should vary which would activate the motor to heat cool on blend door.
If none of that checks out and you have power on both sided of the fuse yo will need to get to the plug on temp switch. With plug connected check dark blue to black green for 12vdc and dark blue to ground.
If that checks go to yellow orange to ground and yellow orange to black green.
Check back with findings or when you get to one of the tests that fails.
Remember the key must be in the run position, the truck does not need to be running but the key must be on.

 

[Rhondasway]

May I piggyback a question related to this? Can the blend door actuator be only partially functioning? Mine does switch from cold to heat, but air doesn't get very hot, especially in sub-freezing temps. Thermostat is working properly and engine temp is normal, no head gasket issue (at this time, lol) and coolant is fresh and full. Also, sometimes it blows warmer than other times.
It is possible that the heater core itself has some oil blockage from multiple blown head gaskets pushing oil through it, but I have cleaned it previously, have replaced the entire engine, and have no oil traces in the system.
I hate to spend the money and tear it down for nothing. Thanks.

 

[DavidC]

I guess I would first try a thermometer, Get it up to normal temp, turn full cold and note temp, turn full hot and note temp, turn midstream and note temp. That would tell you if it only doing a partial swing. I do not know if you can fit anything between the actuator and it's mounts as I marked the metal coupling that is part of the actuator with a magic marker when it was in the middle setting. That way I can see if the actuator is doing some strange things.

 

[GAmes]

Rhonda, IIRC you have a '98. The blend door is operated by a cable, not an electric motor. If you still have the original heater core it might be due replacement. You could always try disconnecting the heater hoses and back flushing it. You might also have an AC evaporator that is full of dirt/hair/leaves that is blocking the air flow across the heater. You can see it by removing the fan.

 

[Chief USA]

This is not an ideal solution and may only partially help but what I did with mine is turn the fan up to max and they crawl under the truck with my compressed air hose and air chuck, found the evaporator drain and gently blew compressed air up into the evaporator drain. A LOT of leaves & other trash came out of the dash vents with the fan blowing on max. I repeated this until I did not get much trash out of the vents.

Again, this is not ideal and not the proper way to clean out the HVAC box but is sure DOES beat taking the dash apart to get in there and has worked well enough for me a number of times.

You would not believe how much trash accumulates in the heater/evaporator box.