34-Eliminating the Heater Control Valve

[fiatslug87]

If anyone has this please post.

[eaglescout526]

Perhaps this one doesn’t exist anymore due to Minuit debunking that having the valve in place with AC setups actually helping with the cooling of the cab. Just a thought. 

[hgeranium]

Guys! In doing some research I have found what seems to be cruiser's writeup on tip #34 if someone was still interested on doing it. Here it is:

# 34 Eliminating the heater control valve in XJs/MJs
Why would you want to? This valve is unnecessary and a source of leaks and complications. Jeep
eliminated it as time passed and so can you. With the valve gone, radiator water flows to the heater
core all the time, but your hot/cold door position blocks it when heat is off or when on AC. Your call if
you must remain original for your year. In which case you probably haven’t eliminated the front axle
disconnect either. Jeep also did away with that!

Here is what the control valve looks like; four hoses to and from the
radiator, and to and from the heater core, AND a vacuum line which
controls the valve. Pull off the vacuum line and plug it securely before you
forget. Your engine will tell you if you forgot!
Now pull the hoses off the valve. These can be discarded, EXCEPT you likely
will need some of the hose going down to water pump so, leave it in place
until you decide if and how much you need and where to cut it.
A big caution: be careful when you remove the hoses from the core inlets
going through the firewall. The hoses will be frozen on, and
excessive force could damage the heater core causing you big
problems! Suggest you cut the hoses close to the core inlets, then peel back a little hose at a
time and gently cut with a utility knife until you can easily twist it off. Note: the core
connectors are different sizes as shown! Bottom about 5/8” and top close to ¾”.
I purchased two Gates hoses as shown for a ’97 XJ, Gates
numbers 19039 for the longer and 19038 for the smaller.
Inspection suggests these are right—good fit! The bigger and
longer hose connects from the thermostat housing, top, front of
the engine and the larger connector at the firewall. The smaller
hose goes on the smaller core connector and comes back to join
the hose going down to the water pump.
Note: this smaller hose only reaches back to the AC compressor
because Jeep brought up a metal pipe in later models alongside
the AC. You probably won’t have that but, you did leave the hose
going down there in place, right? You just need to connect the 19038 up with that hose
using a barbed, 5/8” connector, brass or PVC. You may need to cut the 19038 to fit based on
the positioning of your barb connector.
All you need now is to install and tighten clamps. Couple issues: Some claim the PVC
connectors fail in time. I have never experienced that, but I needed a new one and bought
brass (easy to find—standard garden hose 5/8” connector). Secondly, there is an argument
about air bubbles and water flow with some suggesting that the larger hose 19039 coming
from the thermostat should go to the smaller heater core connector on the firewall. Well, the smaller
hose coming up from the water pump is pressurized, so going to the lower and smaller heater core
connection seems right to me. Also, if you feel the need to
switch them, then you have to cut both hoses and downsize

one and upsize the other on the heater core end! For me, I just install where they logically fit by size, big
end to big fitting, and they look the cleanest with nice parallel hoses. DONE!

[fiatslug87]

@hgeranium nice job finding it and thanks for reposting it.