Questions About Heater Control Valve and Blend Door
 

Hey guys, today my heater control valve broke in my 1992 XJ, so I removed it and bypassed with two hoses like others have done. I have a few questions:

1. Since I have owned the for 6 years, every time I turn on and off the heat or AC, there is a creaking noise that I presume is the blend door opening and closing. Is this noise normal?? Does something have to be lubed or cleaned related to the door?
2. After bypassing the heater control valve, this creaking/door opening noise now happens every time I start the jeep, which never used to happen before. Is this normal after bypassing the heater control valve?
3. There is also a noise when I turn off the jeep that I hear coming from inside the passenger dash, kind of like a fizzing noise, that was not there before I bypassed the heater control valve. The sound goes away a few minutes later. Is this normal? maybe sound caused by a higher flow rate caused by removing the valve?

hoping someone can answer these questions. Thanks

Did you plug the vacuum hose that went to the heater valve? If not or its leaking and losing the vacuum stored in the canister under front bumper. This allows all vacuum operated actuators to relax with engine off, then you start engine and the vacuum recharges and puts the actuators back to selected positiond

I second that!

I covered the vaccume opening with tape

The dorman rack has an assortment of little vacuum parts that will better cap that, the tape won't last. In a pinch use heat shrink tubing pinched shut.

The creaking sounds like the vacuum leak making the motors move faster than before, they can be pretty noisy. The fizzing sounds like the air hasn't bled out of the heater core yet. Factory flows top to bottom so they don't bleed fast, but it will after a few heat cycles.

When your heater core leaks you'll have the chance to clean and lubricate the whole air box and HVAC system. Dash disassembly is a chore but pretty straightforward. You can lubricate a few of the vacuum motors under the dash but I don't think you can reach all of them without taking the dash off. Maybe you can but I've never tried. I just lathered mine in white lithium grease when I changed the heater core and it's been great.

Thanks for reply. The creaking sound has been there since before I bypassed the HCV. It always makes a noise when I turn off the heat or AC

So just to be sure, turning off the heat/AC while the engine is still running will reposition the vents doors. Any doors activated with vacuum, will now bleed off and return to the normal position. Hearing the doors move a bit and the venting of the vacuum is normal (IMO). There is a check valve that maintains vacuum in the system during periods of low engine vacuum (climbing hill, accelerating, engine off). It's normal for the vacuum to bleed off after a few days so you may hear doors moving once you start the engine.

If you have a vacuum leak of bad check valve, you can try the following.

If you have a vacuum pump, you can pull some vacuum on the hose at the intake manifold. Make sure all HVAC controls are OFF. Pull a few PSI and see how long it holds. Then make sure you test at every door position including full cold on the temp selector.

If you shut the engine off and move the selector to different vent settings, you can hear the doors moving. Keep changing until the doors no longer move. You should get a couple of changes until the vacuum depletes. Once you start the engine, you regain vacuum and the doors will move to the selected position. You can also run the engine, select a vent position, then shut down. Come back an hour later and move the vent selector (do not start engine). You should still get some movement.

If it can't maintain vacuum, you either have a leak or a bad check valve. Make sure you check all of the lines, including the ones that connect to the reservoir behind the front bumper. I think on a '92, the check valve is part of the reservoir. If the check valve is bad, you can get a generic replacement at mount it at the line on the intake manifold.