Heater issue

Hi there, I have an 89 XJ. Recently it hasn't been blowing hot air. I flushed the heater core, had good flow, reservoir is full, Is there a way I can check the heater valve?

See if you have a vacuum source to the valve. There should be a pink line from the firewall to the heater valve. If that is disconnected or compromised it won't work.

Yep, was looking at that too. I didnt look to close though. I'll go inspect it. Thanks

I don't know if the '89 still has the metal HCV but the one on my '85 eventually corroded to the point where it would not operate freely.

Ok, which one is the heater valve? Is it the plastic thing with the vac line going to it or the metal square thing?

follow the heat hoses back along the valve cover. They'll go into a wierd valve looking thing that has hoses that go into the firewall (heatercore) and has hoses that go to the Renix Coolant tank on the firewall.

That's the HCV. When you don't want heat it bypasses the flow into the coolant tank.

Ok, found it. Thank you. Ok if I hook up garden hose to upstream side of the valve, with heat ON, it should flow out the bottom side of heater core IF valve is working. Am I right?

Alright. Now I'm reading up on bypassing that valve. From the sounds of it, I still get the heat I need in the mornings, and I can put the temp switch to cool and the air will blow cooler? What's the purpose of this valve?

Chuckanut said:

Alright. Now I'm reading up on bypassing that valve. From the sounds of it, I still get the heat I need in the mornings, and I can put the temp switch to cool and the air will blow cooler? What's the purpose of this valve?

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Eliminate it and plug the vacuum line. The heat in the cabin is controlled by blend air doors anyway. It's intended purpose was to stop coolant flow through the heater core with AC on. Not needed at all.

Oh awesome! My AC doesn't work anyway. But I ended up cleaning out the valve tapped it on the ground and I heard the valve on. Now it works. If this becomes an issue again I'll eliminate it. Thanks everyone

Chuckanut said:

Oh awesome! My AC doesn't work anyway. But I ended up cleaning out the valve tapped it on the ground and I heard the valve on. Now it works. If this becomes an issue again I'll eliminate it. Thanks everyone

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Is it a plastic valve?

cruiser54 said:

Eliminate it and plug the vacuum line. The heat in the cabin is controlled by blend air doors anyway. It's intended purpose was to stop coolant flow through the heater core with AC on. Not needed at all.

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Mostly true... However, if you eliminate the valve you WILL notice a little extra heat in the cabin due to the extra flow through the heater core when not using the heater. This can add to already uncomfortable inside temps without A/C on a hot day.

NotMatt said:

Mostly true... However, if you eliminate the valve you WILL notice a little extra heat in the cabin due to the extra flow through the heater core when not using the heater. This can add to already uncomfortable inside temps without A/C on a hot day.

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Sorry to disagree with you, but I've done this to all three of my Jeeps and I live in Arizona.

That ONLY happens if your blend air door isn't adjusted properly and that's a 3 minute fix.

cruiser54 said:

Sorry to disagree with you, but I've done this to all three of my Jeeps and I live in Arizona.

That ONLY happens if your blend air door isn't adjusted properly and that's a 3 minute fix.

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I guess everyone's experience is different. I'm guessing you probably run A/C in your rig, which I'm sure covers up the bit of extra heat circulating around the cab. On both my XJ and my MJ, with the heater valve bypassed, and NO A/C, there is a discernable difference in temperature in the passenger compartment, especially around the passenger footwell.

I ran my old XJ with the valve removed all winter and finally had to put a new valve in when spring came around since it got too hot inside even with all the windows rolled down.

I'm not saying ditching the heater control valve is a BAD idea, just saying that you will notice a little extra heat inside the passenger compartment. It's a FACT, with coolant running through the heater core it warms up, and DOES create extra heat inside.

It may or may not be worth it to you to have the simplicity of not having the valve, it's up to you. For me, in Central WA (where it gets plenty hot in the summer too), with no A/C, I'll take any reduction in in-cab heat I can, including running a heater core bypass valve.

Well, I get no hot air on Vent or any other setting either. I suggest you look into adjusting your blend air door.