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What is the vacuum switch on a 1999 Chevy Tahoe that controls the heater by pass valve?

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It is the middle switch on your climate control head

Posted on Sep 28, 2009


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Where is the heater control valve located on my 1995 ChevyK1500

it is connected in the heater hose line, normally closer to firewall above exhaust manifold, there will also be a plastic vacuum line running to it.
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Where is my heater control valve located on my chevy 1500 WT 4.3 2 wheel drive pick up Im not getting any heat unless riding down road when I stop it blows cool untill I start driving again

Chevy vehicles do not heater control valves in the water lines any more...they always rust out and malfunction. What you are probably experiencing is a bad vacuum ball or a vacuum tubing leak in the heater box area under the dash. The control lead that you use to adjust the heater (temp and direction), is vacuum controlled from engine vacuum. Engine vacuum varies under load and at idle, so the manufacturer put vacuum balls under the dash to store vacuum for the controls. When you adjust the heat or direction, vacuum from the balls is diverted to vacuum motors that position the blend doors to pass air thru the heater core or A/C evaporator. Other motors direct their door(s) to position the air to the floor, mid-vents, or to the defroster. A leak in the tubing, ball, or motor can cause the door(s) to retract to default if vacuum drops down as it does at idle. Have the heater box and vacuum system to it checked out.

Dec 08, 2015 | Cars & Trucks

1 Answer

Chevy tahoe gets heat in rear but not front

Bad heater control, plugged heater core between heater core and a/c condensor, broken vacuum line to control. Can you hear the gate open and close under the pass side dashboard.

Jan 27, 2013 | Cars & Trucks

1 Answer

1999 chevy tahoe can't change from heater to defrost or to air conditoner stuck in the upper vent positon. What can I do to fix the problem?

It sounds like vacuum is not getting to the vent, heat and A/C controls. Find the vacuum can. It may be under the hood on one of the inner fenders. The "one-way" check valve is usually located in the line and close to the can, make sure it works properly. The valve could be the very thing that's causing the problem. Trace the lines back to the vacuum block at the intake manifold or fire-wall, and also back to where the line goes thru the fire-wall. Check the can for leaks or obvious holes. They used to be just a plain metal can, but it could be a plastic ball. Check the lines as you go, for breaks and rub-thru's. Move the controls thru all settings and listen for vent door movement. Worst case is a bad vacuum motor or air flow position selector switch, and/or a faulty Blend Door Actuator. If you have been driving around with the Temperature knob or control set at the same spot for months, move it from fully cold to fully hot several times and wait for the air temperature to change each time. This will help reset the blend door and vacuum control system. Hope this helps... Let me know what you find.

Aug 25, 2011 | Chevrolet Tahoe Cars & Trucks

1 Answer

1986 chevy elcamino. i am having a problem with the heater blowing only cold air. i changed the thermostat but it did no good. someone told me maybe it is the blend door. how can i tell if it is and how to...

First thing you want to do is check the heater control valve on the engine side of the firewall attached to one or both of the heater hoses. Coolant must pass through it for the heater to work. If the valve is good, make sure you are getting flow through the heater core (you can run a garden hose through it) "blend door" is inside the heater box and is moved either by a small vacuum chamber (looks a lot like the vacuum advance mechanism on older chevy distributors). or it is moved by a cable. Whichever you have, it can be found on the heater box under the dashboard.
Easiest way to check them is to watch the heater box and with the engine running move the heater control Whichever type of actuator you have it should move the arm for the door when you do that. If you find one that does not work (for vacuum ones only) use a hand held vacuum pump and try to make it move. If it does, it's good if not, you either have a bad dash control or disconnected vacuum supply.
If cable type, find out why the cable isn't moving.

Sep 26, 2010 | 1986 Chevrolet El Camino

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On my 1999 Chevy Malibu when you press the switch for the a/c it will drop out if you turn the fan knob to a different setting. The same when you select out side air or recirculate they bounce back and...

it sounds vacuum related the fan knob relates to the fan motor (electrical) the vacuum switches relate to the heater controls hope that makes sense

Apr 09, 2010 | 1999 Chevrolet Malibu

1 Answer

I changed the thermostat, and it is working properly in my 1999 chevy astro van, But it only produces cold air. All settings only produce air from defrost setting. Thanks Keith

Keith Ok you have to check the valve that leads from the heater coolant from coolant to pass heater.Tambien have to verify that the gate which is in the box where the evaporator and heater this work this work with vacuum and if you have no way of vacuum to the actuator you will have no calefaccion'Thanks

Jan 30, 2010 | 1999 Chevrolet Astro

1 Answer

My 1995 chevy van blows out cold air when i have the heat on

The hoses to the heater core may have been re-plumbed to by-pass the heater core (a temporary fix to a leaking heater core) verify that hoses are routed properly. If they are, check coolant fluid level....when it is gone...the heater will not blow hot, and you will likely burn up the engine (if coolant is gone...temp gage may not register "hot" because there is not fluid for the temp sensor to measure. may have a broken/cracked vacuum line (the valves for switching where the air gets directed are typically vacuum controlled) Hope this helps.

Oct 12, 2009 | Chevrolet Astro Cars & Trucks

1 Answer

My 1999 chevy tahoe will only blow hot/cold air at your feet. It will not change locations

there is a valve on the bottom of your dash it is all black plastic cover in the center, tap that with your fist the valve might just be stuck. if not check your controls does iit click when you move them if not your a/c controls might be brocken..

Dec 16, 2008 | 1999 Chevrolet Tahoe

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