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!997 Dodge B2500 3.9L- What controls the vacuum TO the ac/heater climate control switch in the dash?

Have been looking for a vacuum leak. Found one in the engine compartment at the throttle body but no others in the engine bay. Van still stalls all though not as much. Cannot get heater to blow from vents- defrost and floor only. Figured this was at least one other leak. Took dash apart and removed heater/ ac control panel. With van running and heater set to "Hot" and switch set to "heat" there is NO vacuum from any vacuum line at the switch OR at the heater control valve. The hose is on the intake and no leaks have been detected there. Is there anything between the intake vacuum outlet and the heater/ac control panel on the dash that controls the vacuum on and off? Checked for any hoses that might be disconnected but did not see any.

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  • Cars & Trucks Master
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The switch that controls this is the vacuum mode switch and it is in the heater control panel on the dash.

Posted on Mar 21, 2017

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Posted on Jan 02, 2017

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SOURCE: vacuum leak

Your air leak is in the heater control switch. You have to replace this unit. I have done this in both S10 Blazer and S15 GMC. Remove the front dash cover and remove the control bolts. One control is electric and the other is air controled. You can get this unit from GM or take your chance and buy it from the wrecking yard or off EBay.

Now some one also posted that there 4X4 is not working also. This uint is controled by electronic control. The transfer case has a electric motor on it and is control by the switch on the dash only. There is a canister outside under the front right (pass) side fender that controls the locking gear for the front drive axel Chech this for air leaks.

Now for the banging in the heater unit. It is the blower motor. I have the same problem right now in my S15. It needs to be changed.

Posted on Jan 13, 2009

chuck943
  • 783 Answers

SOURCE: Vent control

You have a vacuum leak.Defrost is the default postion(no vacuum).
See if you can locate the small black vacuum line that goes inside the vehicle on the passenger side near the heater core. The trace it back,should see it going to a canister then to the intake manifold.Make sure it is not disconnected or broken somewhere.

Posted on Mar 02, 2009

  • 16 Answers

SOURCE: No air blowing from the dash vents

sounds like you have a vacuum problem

Posted on May 04, 2009

  • 87 Answers

SOURCE: 04 Chevy Tahoe Climate control issues.

HVAC control head problem or it is the air Temp Control Valve problem. THe control head is the one with the buttons and knobs and the control vavle is located on the HVAC carrier assembly underneath dashboard (two of them one on left and one on right in center). This is a job for someone who has knowledge of HVAC and electrical on a GM vehicle.

Posted on Aug 02, 2009

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1 Answer

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1 Answer

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