heater control valve not working

Katiness · 04-18-2011, 12:50 PM

I have a 1990 XJ. We replaced the overflow tank on my jeep. Since then my heater only has air come out of the defroster. We took off the heater valve and when you blow in it, it moves properly so I think we must have a vacuum leak. We have checked the lines around there but can't see anything. Does anyone have any suggestions on which lines to look at. Maybe it was just a coincidence and it's another vacuum line. If anyone has pictures of lines I would appreciate it

xjfever · 04-18-2011, 01:25 PM

The air coming from the defrost only is a direct sign of a vacuum problem. The hose for both runs from the canister behind the front bumper on the passengers side up below the battery tray, to the cruise servo if so equipped, then back to the firewall along the passengers side inner fender. It splits out to the heater valve, either before or after it goes into a check valve and then into the firewall to the heater controls. The most common place for it to fail is at the battery tray where corrosion eats away at it, but with it's age could be damaged anywhere along the way. The cannister could be bad as well and needs to be checked, it looks like a plastic egg and sits inside the bumper behind the inner fender.

Paradise XJ · 04-18-2011, 01:45 PM

Is there a vacuum line on your HCV at all.

If not, it's the pink/tan/light colored one. If so, go forth with the above.

Katiness · 04-18-2011, 10:19 PM

There is a pink/tan/light colored line connected to it. Are you saying it's defective? It goes to the firewall. There is no vacuum at that line. We checked the cannister and it looks good. We have vacuum past the battery. I hate vacuum leaks.

**tjwalker** · 04-19-2011, 05:44 AM

And once you get that vacuum re-established to the heater control valve, consider replacing that valve unless it is newer. Money well spent.

These valves were under-designed from the factory and failure of them is extremely common, not to mention that when they disintegrate, it can lead to an overheat and engine damage.

Katiness · 04-19-2011, 05:03 PM

Good idea to replace the heater control valve. I don't know how old it is. We are still looking for the leak
Thank you for the input

Katiness · 04-19-2011, 07:17 PM

Ok, we found a blue line not plugged into anything. We cannot find where it goes. I posted a picture down below. If anyone can post a picture or tell us where it goes it would really help.

jheld95xj · 04-19-2011, 07:43 PM

its hard to tell from the pic but that might be the actual vacuum line that hooks to the junk heater control valve that controls your heat, that might be your problem right there. I'll see if i can post a pic of mine to show you where it hooks up, but it hooks to the canister part and it looks like the nipple is broke off on yours.

jheld95xj · 04-19-2011, 07:54 PM

here's mine, as you can see the vacum line hooks to the the heater control valve on the canister part

Katiness · 04-20-2011, 09:11 AM

Thanks, but that is not the line I am talking about. I have a pinkish tan line connected to the HCV. I was wondering about the blue one. It is going off toward the overflow tank. I looked in a friends 90 jeep and it doesn't go anywhere on his either. So I guess we are back at square one. We will have to go back and recheck everything.

Katiness · 04-23-2011, 04:19 PM

Yeah! I found it!. Thanks for all the input. It was the black line leading into the firewall.

xjfever · 04-23-2011, 06:36 PM

glad you got it fixed.