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ADJUSTING THE HEATER CONTROL VALVE - HR-101

At 10:07 PM 7/19/04 -0400, Chuck Jackson wrote:
>".... in July, I really donít need the extra heat (I think it comes from the heater, not a heat transfer process from the engine compartment). I have seen fixes that involve ... Why not put a ball valve in .... Shutting off the ball valve should remove any water flow and therefore any heat transfer at the heater core. .... Does that make sense to you?"

Nope. Waste of money for no gain. Most attempts to modify or replace the valve are aimed at increasing the water flow when it's open. Just adjust the cable so the heater valve actually shuts off in the summer time. I get cool air ventilation out of my heater box all summer long.

heater control valve
Heater control valve in closed position

Move the heater control to the extreme cool position before starting the engine when cool. Start and run engine up to normal operating temperature. Place your hand on the heater supply hose (between valve and heater) If the hose is cool the valve is fully closed, If the hose is hot the valve is not closing.

A "feature" of the MGA setup is that the heater valve has a little more physical travel than the cable connected to the temperature control lever. In the winter you might prefer to have the valve go full open, even if it doesn't close all the way. In warm weather you would prefer to have it go full closed, even if it doesn't open all the way. To that end, here's how you get it to go fully closed.

Move heater temperature control lever to the full cold position (hard left). Loosen both cable screws on the heater valve. Push the cable forward to move the center wire through the wire nut until the outer jacket touches the lever, and tighten the screw in the wire nut to secure the center wire. Then pull back on the cable jacket until the valve goes to the full closed position, and secure the cable outer housing clamp. To the best of my experience, this will always make the valve completely shut off the water flow, and no funny modifications are required.

One word of caution. If you mount the temperature control lever mechanism upside down, it works backward, which can be very confusing. When you move the lever to the left it should pull on the center wire. Moving it to right should extend the center wire.

And by the way, even with the heater turned completely off and cold there will be a lot of heat coming though the single layer of sheet metal on the heater shelf and upper firewall. For the tunnel with a single layer of carpet and no carpet padding, your leg resting against the tunnel can get very uncomfortable from the heat. Imagine how hot that might be without the carpet, and that's how hot the firewall gets.

Insulating the bottom of the heater shelf and the back of the upper firewall can cut heat intrusion dramatically in hot weather. Also keep the 4" air hoses (plural) in place so you can open the heater vent and run the blower for fresh air ventilation around your legs.

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