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Heater Control Valve
Phil Singher

Well, we finally got around to refurbishing the heating and cooling system on our 122S. Not only was the radiator shedding fins with every bug strike, but coolant was slowly disappearing -- somewhere. We eventually noticed that there was no loss as long as the heater was turned on, even a little bit. What with the long winter we were having, that presented no problem, but we couldn't figure out where the water was going. Finally, we decided the heater core was the culprit.

When Boeing builds a 747, they start with the central fuel tank and build the rest of the airplane around it. When Volvo built the Amazon, it seems they started with the heater core. We flushed the cooling system to get any crud out of the block, and then, after some study, took everything apart. The radiator and core went out for rebuilding, and we spent the next several days cleaning up the rust on the heater housing and giving it a nice satin black finish.

By the next weekend, we had everything put back together and sealed up so tightly nothing larger than a helium atom could possible leak through. We installed new high-temp heater hose throughout, and put in a new thermostat. We filled the system with distilled water, opened the heater control valve, and started the motor.

As soon as the car warmed up and the thermostat settled down, we turned off the heater. Psssshh! Water sprayed on the passenger's rubber floor mat. We turned the heat back on. No water. So, it was the control valve after all -- the "No Longer Available" control valve with its thermocouple firmly sealed into the heater housing, which would have to come back out of the car to remove it. What to do?

The answer came from the RPR catalog -- retrofit a new control valve from a 240. The new valve looks different from the old one, but it is easily adapted. We drained the system once more, cut off the old valve's thermocouple flush with the edge of the heater housing, removed it and threw it away.

The old valve's mounting plate is rectangular, with a mounting screw hole at the center top and bottom. The new valve is the same basic size and has the bottom screw hole, but the top edge is angled and has no hole. We took a small round file and carved a notch into the angled edge to accomodate the mounting screw.

The control cable attaches differently -- we used needle nosed pliers to uncoil the cable end, and then clipped it to slip through the new valve's clamp. The cable sheath attaches identically on both valves.

The original formed rubber hose to the heater core cannot be used with the new valve -- happily, we had some of the new heater hose left over. It was easy to make an appropriate loop to replace original hose.

The new thermocouple wire is too short to reach the inside of the heater housing, so there would be no point removing and opening the housing in any case. We pushed it between the housing and the firewall, down by the air flap. Do these actually do anything? We were warned not to cut the wire.

The heater now works excellently.

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