2nd Gen Non-Engine/Transmission Heat/AC Temperature/Blend Control

[jgallentine]

I can only get full hot or full cold air out of my HVAC system. I have watched the blend door motor shaft while adjusting the temperature and this is what is happening. I start out of full cold, turn the know slowly towards hot (notch or two at a time) and nothing happens until I get to about the middle of the knobs adjustment range, which should be warm air. At that point, the blend door starts moving so I stop moving the dial in order to see how far it will go. The door doesn't stop moving until it gets to the full hot position. I then proceed to keep turning the dial slowly toward full hot and obviously nothing happens.



I was able to loosen the blend motor far enough to disconnect it from the blend door. The blend door seems to move freely from hot to cold with no binding.



I put another heat/AC control panel in that I got at a salvage yard and everything performs the same way with it installed.



The only other thing I can see to do is replace the blend motor. I have a service manual and it talks about a resistor but nothing else other than the control panel in the dash and the blend motor. Does the resistor have anything to do with temperature or is that just for the fan? Is there something else that might impact this?



Any ideas would be greatly appreciated!



Jeff

 

[Joe G.]

You may have a collapsed vacuum plastic pipe. If it's not all the way blocked it might do that. Easy to check so might as well do that first before messing around under the dash. The place it happens is above the exhaust manifold before the pipe goes through the firewall. There is a connector there. The bad part of the pipe may be inside the connector. If that's the problem just clip the bad part out and put it back together.

 

[JasonBrown]

If you replaced the electronic controls this will have to be calibrated. I had the same problem with a dodge caravan. I had a bad temperature controller, after replacing with a salvage yard unit it did exactly what yours is doing which is going all hot to all cold. The dealer has a computer program that will calibrate your electronic switch to the motor.

 

[jgallentine]

Jason,



I had this same problem with my original control but this may still make sense. When I replaced my AC core I took the servo motor apart, something I wish I had not done now. I have had problems ever since. I know it did not get put back together and reattached to the blend door synchronized to the same spot. Further, the coupling between the servo and the blend door broke allowing the motor and door to change synchronization further. I have replaced that coupling and am left with the current issue. Would this cause the control to need recalibrated even though nothing was replaced?

 

[jgallentine]

Joe,



The blend door on the 99 is electric rather than vacuum. The vent selection knob is vacuum and it works fine. At this point, I wish the temperature control was vacuum as well.



Thanks



Jeff