there is one on my 91, and all other gen 1's i have seen
john

and all the ones I've seen, too, dside footwell high right, behind a black cone shaped plastic cover that's held on by one screw on the back side, IIRC. It's a ball valve, too.

Gotta have some kind of valve, or intense psychic powers to hold the water back...

Found it on the GenI in ASA. Hate it when those 2 are right... P/N MB272294 Valve, Heater Water. It's in one of the pipes that goes into the heater core itself. The one with the little stubby piece of hose on it.

Oh well, it was fun while it lasted. Guess I'll go ahead and put the compressor on now....

BUT, pcc has a '92.

John B.

I'm pretty sure I don't have a heater valve but I guess the easy test would be to set the heat control to cold then feel the heater core hoses on the firewall, if there is a heater valve, and it is operating properly, then one hose will be much cooler than the other. If no valve then both hoses should be the close to the same temp.

Ok so I installed the valve (NAPA 6601413 $21) and did some driving with temperature readings. These numbers are with minor rounding as I was dealing with driving in some sun and some shade as well as a slightly rising morning temperature. Doing any testing in park with the hood open will produce bad numbers as the air intake along the windshield just sucks in hot engine air. No picture as this is so simple a picture wouldn't provide much more information.

Ambient Temp - 74F(shade), Upper Vent Flow, Fan 3/4 Speed
A/C Off/Outlet Air:
Valve Closed - 82F
Valve Open - 82F

A/C On/Outlet Air:
Valve Closed - 46F
Valve Open - 46F

As you can see there is virtually no difference with or without the water valve. For sure it cuts off hot water to the core, with the valve closed I got no heat when temp dial was set to high. But the heater hoses at the firewall were the same hot temperature, maybe because there was still flow to the throttle body and that was enough to heat the hoses.

The center console pocket was cool with the valve closed so there is definitely less heat in the cabin to cool, but over all Mitsubishi did a great job just using the blend doors to distribute heat/cool.

You can draw your own conclusions but this little project did not produce what I anticipated - about a 5* difference in A/C air. There is less heat in the cabin, so that might make me feel cooler, but the numbers did not show this to be a worthwhile modification. I'm glad I only chose the $21 valve and did not go with a more expensive remote control one. You also have to understand that the compressor cut off temperature will not change as this is determined by the temperature sensors in the evaporator box, maybe this is why the outlet temp is the same.

Hope this has been helpful.

I do not know if it would make to much of a difference, but if you put a vlave on the inlet and outlet and turn them both off you should help at least to cut off any abient heat that would follow the coolant back to the heatercore. I noticed on my montero even with the heat off that the outlet hose was very warm and the inlet was even warmer. Just an idea.

I'm not sure where the heat transfer is occurring that makes the two firewall hoses the same temp (to touch) when the valve is closed, but the fact that I get no hot air when the valve IS closed shows not much if any heat is conducting to the heater core. The valve is all metal so it will even conduct heat.

I know it's a king-kong-mega-biotch to get to the heater core itself, but I'd be curious to know what the core temp actually is during the tests you performed.

Well with the valve closed and the temp control knob turned all the way hot it can't be much because I only got 82F outlet air.