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Randall C
Randall C, ASE Master Tech
Category: Chevy
Satisfied Customers: 12719
Experience:  ASE Master, L1, 32 years, Diagnostic / Electrical Specialist
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Where does the vacuum hose on the heater control valve connect

Resolved Question:

Where does the vacuum hose on the heater control valve connect to on a 1997 Suburban 2500 4WD 454 engine with rear AC?
Submitted: 6 years ago.
Category: Chevy
Expert:  Randall C replied 6 years ago.
Hello, how long of hose end do you have? what end is undone?
Customer: replied 6 years ago.
I replaced the heater control valve because the old one broke. The vacuum hose attached to the old valve was disintegrated and the end away from the valve wasn't attached to anything, so I don't know where it goes.

There is a small cylinder (roughly 3/4" diameter and 1.5" long) attached to the firewall above where the coolant lines go thru the firewall. It has an electric plug and 2 small hose barbs on it. From what I read elsewhere, it sounds like that might be what applies the vacuum to turn on the heater control valve. I'm guessing that it electrically opens a valve that allows vacuum from the engine to be applied to the heater control valve. But if that is the case, then there is another vacuum hose missing on the second barb fitting on that cylinder, and I need to know where that goes, and whether the hose to the heater control valve attaches to the top or bottom fitting on the cylinder, or whether it works either way.
Expert:  Randall C replied 6 years ago.
Thanks. yes, the hose from valve to solenoid goes on botton fitting. the problem is i can not lcoate anywhere a pic of where the other hose goes to/from. i will say, the line to the top fitting is to be MANIFOLD vacuum so it goes to engine directly on or near throttle body OR look at rear of engine near the fiel pressure regulator that has manifold vacuum as well . There may? be a "T" fitting there, look at the underhood vacuum diagram label which shouild be on or near on top of radiator? they put the label in different spots. the valve is not very important at all. It only turns off water to heater core to help AC cool a little better in very hot weather. I understand you want done correct but.. I just do not remember nor pictures to show where other line hooks up. I would look around back of engine etc as you may find the balck/hardplastic line laying somewhere. If not. look close at throttle ody for empty vac fitting and look near fule regualtpor as well for fitting. if all else fails, get a vacuum T from parts store and insert inline to the Fule pressure regualor hose. It will do exact same thing. the top fitting is to be full vacuum when engine at idle

Customer: replied 6 years ago.
Thanks for your answer. That certainly answers the first part. As to where the vacuum hose from the solenoid goes, I did not find any fittings or hoses around the throttle body. There is a small, black, hard plastic hose that goes across the top of the engine. It is unattached on the passenger side, and broken off on the driver's side. I can't find where it might attach on the driver's side. Any ideas?

There is a slightly larger hard plastic hose going from the large black cannister behind the left edge of the radiator over to a square thing with an electric plug sticking out of the intake air manifold on the driver's side. Is that the vacuum line to the fuel regulator? Tapping into that would require a tee where the leg of the tee is a smaller size.

Here in Tucson, we do have very hot temperatures, and a Suburban has a very large interior volume to cool.
Expert:  Randall C replied 6 years ago.
Did you look at under hood label? I will be the smaller vacuum line One end goes to solenoid, other, you have to find a fitting or T that may have broken off on one end. i wish i could give moe info but just can not remmeber without looking.
Customer: replied 6 years ago.
The label is on the air filter housing. It indirectly led me to an empty rubber elbow coming out of the air intake manifold, which has suction on it. When I connect that directly to the heater control valve, the valve activates. When I connect it to the solenoid, it doesn't, so there is an electrical problem. But I already knew that there are electrical problems with the AC, because I have to bypass the AC relay with a jumper wire for it to turn on. I guess I could leave the vacuum line attached directly during the summer, and connect it to the solenoid during the winter.

Thanks for your prompt help. I will click "Accept" after I send this.
Expert:  Randall C replied 6 years ago.
yes, sounds like electricl problem maybe at conttrol head etc. Glad you found the vac source. Yes.. it is to have fulltime vacuum like you describe. soory you had to search some but info is very limited due to age
Expert:  Randall C replied 6 years ago.
here is a diagram for reference. the HVAC control module may very well be your underlying problem. Idoes control compresor funcyions as well as heater control valve. it is a micro processor

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