HCV solenoid not getting power

DWAYNEDETERMAN

MEMBER
1999 GMC YUKON
5.3L
V8
4WD
AUTOMATIC
200,000 MILES

The heater control valve is not opening. There is no vacuum to it. There is vacuum to the HCV solenoid. The solenoid has ground but not power. I do not know which wire in the climate control unit in the dash should feed this, nor do I know if it is a direct feed, or if it goes somewhere else first. Fuse 12 is good. Suggestions and a good wiring diagram would be appreciated. Thank you.

5 Replies

HMAC300

MECHANIC
48,601 POSTS

Are you sure this is a 1999 as it does not show any water valves or solenoids. Has to be an earlier year as we do not show it on diagrams.

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Saturday, October 8th, 2016 AT 3:50 PM

DWAYNEDETERMAN

MEMBER
4 POSTS

Yes, this is a 1999. My understanding is that there were two models that year (mid year split) and that this is the early half. I suspect that it would be the same as a 1998 model.

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Saturday, October 8th, 2016 AT 4:00 PM

HMAC300

MECHANIC
48,601 POSTS

Okay I found it, only on certain models I sent diagram. We do not have a vacuum diagram for it though. The gray wire is power to valve and black to ground on head. See picture. It may be a bad control but have you scanned it for codes?

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Saturday, October 8th, 2016 AT 5:06 PM

DWAYNEDETERMAN

MEMBER
4 POSTS

I do not have any codes. The gray/black wire coming from the control unit does not have power on it. The original control unit did not have power on that circuit either, which is why I picked one up at the salvage yard. If it is a problem in the control unit, I suppose both could have the same problem.

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Saturday, October 8th, 2016 AT 5:33 PM

JIS001

MECHANIC
3,411 POSTS

They could especially if it is a common problem. Had an issue once on an infinity G35 the drop down function for windows did not function. Recommended the latch assembly and they brought me used parts from the salvage yard. After removing the glass installing and adjusting glass same problem. They go to the dealer and they tell them is the latch assembly also so they did it with new parts and problem fixed.

Now given the year on your vehicle some parts may not be available from the dealer but checking online there are places that might actually be able to repair your control unit.