Subject: Check voltage going into heater valve Author: cheung1 as Patrick C 88 750 160K : member since March, 2004 : 836 posts Posted on: 2008-05-16 21:35:12

There are three pins going to the heater valve assembly. The mid pin is common, at 12V (when car running). The outside pins each conceptually go to an output transistor on the IHKA board. The solenoid defaults to a power-off state of letting antifreeze pass through. If the board wants hot water, it will turn on the corresponding transistor which in turn short the pin to ground. Now electric current will flow from the mid pin through the solenoid coils to the side pin and energize the solenoid. The plunger will thus be pushed into the fluid stream and cut off flow.

In summary, if you measure 12V DC or so across pin 2 and 3, or pin 2 and 1, then that side should have the flow cut off, and hose should stay cool. Now if you see the above voltages, but hose is warm, then the plunger inside is not doing its job. If this is an original heater valve assembly I would buy a new one and change out the entire assembly. This is because the nylon nipples connecting to the hoses especially the source inlet one is probably quite aged and brittle. In fact if you don't cut the hose to detach it from the nipple you are likely to break the nipple off.

Lastly, removing the heater valve assembly give you a good opportunity to access the hose clamps to change out the five or so hoses involved. Except for the 3-way hose, the other ones are relatively inexpensive. Definitely change out the source hose between engine and pump/assembly because it had seen the highest heat and will be the first one to burst.

Patrick C 88 750 159K

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