shum8

Ok day one of our project Jeep was good. Got new thermostat housing and thermostat installed. So now....It seems as though the HCV or the heater core is stopped up. No heat inside the cab and the return line isn't hot. Could anyone explain how to remove the heater control valve? Is it made onto the metal lines? I have a heater core but wanted to get some info on removal of HCV before I dove off into the dash. 88 model Cherokee 6 cylinder. Thanks

1991Jeep_Man

I'd bet your heater control valve is shot or there is a vacuum leak causing it not to open and allow coolant to flow. The HCV is evil and should be killed with fire and tossed into the fiery depths of Mount Doom in Mordor.

In all seriousness, eliminate it. Serves ZERO purpose and Jeep realized this in I think 1995. Just either replace the heater hoses with longer ones or just use a barbed connector and hose clamps. Remember though that the hoses are different sizes for the input and output of the heater core. Match them accordingly. I doubt your heater core is plugged. Eliminate the HCV and then do what I did:

Use compressed air or anything to blow out the heater core by using the connected lines that would normally go to the heater control valve. Then, pour some radiator cleaner (I bought from Walmart made by Prestone) and hot water into the heater core. Plug the hoses and let sit for about half an hour to an hour. Go back, run water (I used my garden hose) through the OUTPUT hose to push back all the gunk the same way it came in through the input line. HAVE THE INPUT LINE IN A BUCKET OR SOMETHING! Flush it good, then go ahead and hook back up the lower line to the rest of that line (eliminating the HCV). Take the input top line and hold it up. Poor coolant into said line until it wants to overflow. This helps eliminate air bubbles in the heater core which take forever to clear out. Then quickly hook back up the upper hose. Done!

shum8

Ill give that a try. I don't recall but does it have a vacuum line and a power wire hooked to it? What do I do with those. Its awful busy under the hood. Lots of stuff goin on. I did manage to find the vac hose going to the Vent/AC/Def selector broken. Works great now. Thanks for the info.

1991Jeep_Man

Its a vacuum hose that hooks to the top of it. I just shot some rtv up in mine to seal it.

shum8

Ok the heater control valve is out. I just cut it off T and used longer hose and out 2 clamps on it. It has no barb on it but seemed very tight. Anyone ever tried this? And please tell me no issues. Thanks

ZINGGG

I'd go get longer hoses so you dont have to jimmy rig it for a potential leak. But that's just me.

Go grab some hoses for a 97-01 (when they started eliminating the HCV from the factory)

shum8

Where could i find microfishce or a schematic so i could see what one looks like?

cruiser54

This?

shum8

Ok I didnt realize the newer ones didnt have a tank. If and when I need a radiator. Can I upgrade to one with a radiator cap and do away with all the tank and T fittings? Right now the electric fan isnt working. Antifreeze is circulating good. At idle its running around 205-210 on temp. When I rev it or drive it the temp comes down to 195. Hopefully the electric fan will work. Would 2 electric fans be better?

havensov

Just disconnect the vacuum line and flip the switch on the bottom. HCV uses the vacuum to shut it off, no vacuum and hot coolant will flow through the heater core.

They do serve a purpose in those models as the evaporator for the ac and your heater core are on the same blower flow. So if the heater core is hot you will have poor ac.

cruiser54

Not true. The HCV can be eliminated with no issues with the AC. Take it from a guy in Arizona who has eliminated more than a few HCVs. .

1991Jeep_Man

x2 even the older xj's still used blend doors to direct flow through either the heater core or evaporator core. HCV was kinda like the front disco CAD dana 30... a useless accesory.

cruiser54

Absolutely correct. Redundant systems that cost more and caused issues down the road. Ditch CAD and HCV. Don't look back.

havensov

Hmm, I dont doubt what your saying, and I will admit that my info comes from alldata and Mitchell diagrams and I have yet to tear apart a full dash (thats later this week on my '93) but I have had issues with my ac when the HCV was bypassed on both a '92 and '89. Makes me wonder if the blend door had been tampered/broken/removed on those vehicles.

Either way, the op should have plenty to go on now.

cruiser54

As long as the blend air door is adjusted properly, you're good to go.