The Heat Is On in Greg's Dakota Sport

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Dear Tom and Ray:

I had a heater core on a '99 Dakota Sport replaced, and I now have heat all the time without it being turned on. I was told that I was feeling heat from the engine because there is no insulation on the firewall. I didn't have this problem before the new core was installed. What, if anything, did they forget to do?

-- Greg

TOM: Boy, you're an understanding guy, Greg. They give you a song and dance like that, and you say, "Okey dokey," and walk away. We could use some customers like you!

RAY: That's not heat from the engine bleeding through, Greg. That's heat from the heater. And it's likely the fault of the guys who changed the heater core.

TOM: But before we conclude that they're absolutely to blame (we'll get to that soon enough), let's look at one other possibility. The heater controls in this truck are operated by engine vacuum. There's a check valve under the hood that helps the system maintain vacuum during hard acceleration.

RAY: Right. So if that check valve were broken, your blend doors (the flaps behind the dashboard that regulate how much heat comes into the cabin) can pop open during hard acceleration.

TOM: So if you're getting a surge of heat only when you're accelerating hard or climbing a hill, then this five-dollar check valve could be the problem.

RAY: But if you're getting heat all the time -- which is what you say in your letter -- then these guys screwed something up. Maybe they jammed a blend door so it can't close all the way. Or maybe they forgot to reattach a vacuum hose.

TOM: The reason they're trying to get rid of you is because rescuing the Chilean miners was easier than getting to the heater core in this vehicle. They don't want to do it again. For free. So they're hoping you'll just go away, or start driving around in your bathing suit.

RAY: So you're just going to have to be a little more insistent when you go back to see them, Greg. Bring a couple of large friends with you. Or a lacrosse team.

TOM: They don't want to take out the dashboard again, but that's what happens when you screw something up -- you have to do it again until you get it right.

RAY: Sure. Ask my brother about his years in eighth grade.

Comments

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timasemaster

Sun, 2012-02-26 14:32

Have you guys ever had a dash out of one of these trucks or serviced anything in the HVAC system? Your reply certainly makes me think you never have and did not bother to look in Mitchell or Alldata before spouting off on this truck. I specialize in HVAC repair and electrical diagnosis. I have also serviced more Dakotas and Durangos than I care to admit. Yes, the MODE doors and RECIRC door are vacuum controlled on this platform, but the temperature blend door is most certainly not. It is controlled by a push-pull cable. To remove the dash on one of these trucks, this cable must be disconnected. Your options are to disconnect it at the HVAC plenum once you have the dash rolled back, or you can remove the instrument cluster bezel, remove the control head, and disconnect the cable from the control head and snake it out of the dash. The problem is most likely somewhere in this cable. Other possibilities would be a faulty control head, or a blend door issue in the box. An outside possibility is that the repair shop used an aftermarket heater core that does not fit properly and is interfering with the blend door. Our shop does not use aftermarket heater cores on this application because they do not fit properly (ask me how I know). I agree that the problem is in the blend door or control somewhere, but certainly not due to a vacuum issue. If the vacuum check valve was faulty as you stated as a possibility, the mode position (floor, panel, defrost or mix) would be changing as engine vacuum changed under load. Please do us all a favor and at least research a problem before spouting off on it.

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