AC and heater blowing at same time


I have a 2000 Dodge Dakota and the AC hasn’t been working. I took it to a mechanic. They vacuum tested it added stop leak and recharged the Freon. However it’s not blowing cold air. They said that the blend door is not shutting off the heater core and allowing just the cold air to blow. Therefore I have both hot and cold air which is creating nothing but warm air. They said a $500 job and the dash must be taken apart to fix everything plus they want to replace the evaporator and heater core while in there.

However for right now wouldn’t a quick fix and maybe also a check be to block the heater core? Then the hot coolant won’t be coming in and only the cold air will blow? Is this correct. Can I do this in a way that I just re hook it up when Winter gets here? The heater core is not leaking. I just need to block the hot air and keep only the cold air coming in the cab. I do basic repairs and can handle blocking it off just trying to stay cool and save a buck right now. Let me know if this will work please.

It can be done. You just take off the hoses going to the heater core, and then install a hose connecting the two engine-side heater core connections together, bypassing the core. Undoing it is the reverse of doing it. But you’re gonna lose coolant when you do it, so you’ll have to replace that.

I’m curious why they want to replace the heater core and the evaporator. If they’re saying the whole problem is the blend door, why do they want to replace other parts?

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I would immediately connect the heater inlet hose to the heater outlet hose and enjoy cool air while checking into the best alternative to repair the truck. But then I am criminally pragmatic.

you can get hose pinching pliers to block the coolant flow through the heater core to check if this is the issue.

You can also turn the a/c on and feel the low pressure line- if it is cold, the a/c is trying to work properly. Make sure you grab the correct line though, as the high side will be hot. Be careful doing this. :slight_smile:

Hose pinch off Pliers- Harbor Freight

Thanks guys I really appreciate your input. Yeah I’m kind of wondering why they want to replace the other parts that are okay too. I’ve heard a lot of mechanics say while there doing one thing it’s best to replace other parts…I understand they might go bad later down the line but to me I live by the “if it aint broke don’t fix it”…

So I’m planning on not going back to this mechanic and blocking the heater core or doing the test as mentioned with the pliers and feeling the line. Thanks for the help!

The blend doors are probably vacuum operated. Has it been determined the problem is at a specific place under the dash? Or is it simply a disconnected or leaking vacuum hose between the engine and the firewall?

That means there is a leak somewhere, which I think is why they are recommending you replace the evaporator. Dunno why they want to replace the heater core.

did you ask?

Please don’t take this the wrong way . . .

Are you the kind of guy who will pay to replace the timing belt only, but not the tensioner, idler and the water pump, which may be driven by the timing belt?

Everybody’s entitled to their own opinion

I’d like to hear yours


I believe the shaft on the blend door is metal, unlikely that it broke. If you remove the heater controls and the radio you can reach in and check the operation of the blend door on the top of the heater box, you might find that the control cable is broken or disconnected.

Hello everyone,

I know the basics of cars/ trucks. Not much of a mechanic when it comes to big jobs. I do basic repairs and if I can figure it out online with the help of youtube, forums and websites I usually do the repairs I can handle myself with the tools I have. Do answer the question about the timing belt…Yes I would replace all those things and not just the timing belt. Although I generally shop for vehicles with timing chains. I had a firend withj a 2005 Dodge Neon where the timing belt broke at 70,000 miles ruining the engine. I prefer timing chains. However to get back to the question…I agree in some jobs multiple parts should be replaced. However I explained to the mechanic that the heater core at recently been replaced and is brand new. He still insisted on replacing it.

I don’t know much about the ac and obviously I don’t the tools needed to repair the ac. Which is why I took it to the mechanic. However I do hate bringing my vehicle to a mechanic because I don’t trust any of them. Especially where I live.

I went to a new place yesterday for the AC because some of the other places I had went years ago were not very trustworthy.

But anyway I think this guy is a joke. The AC compressor has been operating correctly. It’s been coming on however he vacuumed tested the system yesterday put dye in to check for leaks, stop leak and also recharged the system. Once he did this he checked and it still wasn’t cooling so he says its the blend doors. Instead of blocking the heater core I just closed it off with a rag wrapped around the hose and vise grips. No coolant coming in to the heater core. There is still no difference.

The I went and checked the compressor to make sure it was coming on. It is now not coming on. I feel like he did something to stop the compressor from coming on and the system would work properly. And he plans on charging my $500 to fix the blend door and replace the other parts when the compressor either needs replaced now or he did something to prevent it from working properly.

I checked the fuse and I’m getting ready to go back out and check the electrical connections. It seems like a scam to me. If he charged the system and the problem is the blend door why is the compressor suddenly not coming on? It was comng on when I brought it to him. I assume there is just one fuse to the ac clutch and unless he cut a wire the electrical connections should be okay. I’ll updated you after checking.

And I will look into removing the radio the check the blend doors. I seen something online about that yesterday…Also kind of wondering why he didn’t want to do this before tearing the dash apart and charging me $500. Well I guess I know why he wouldn’t have.

If the system is low on refrigerant, the compressor won’t come on. So, he didn’t have to break the compressor in order to get it not to come on if the evaporator has sprung a leak, for example.

My main question is that I want to know why he has reached the conclusions he has reached. This does not necessarily mean that he is wrong, or lying - it is entirely possible for two problems to exist simultaneously and the blend door won’t move at the same time that you have a leak in the system somewhere.

But you need to know why he thinks this because while he may be entirely correct, he might also be one of those “throw a bunch of parts at it and see what sticks” guys.