Question about 1994 GMC Sonoma

1 Answer

94 gmc sanoma. heater dampers do not work properly. can hear a vacuum leak at rear of heater control switch. new switch at dealer is not available,junk yards no luck. the vacuum hose configuration is what i can not match up. please help.

Posted by on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • GMC Master
  • 975 Answers

From the feed line under the hood,have an
assistant(engine off) blow cigarette smoke into the line,you should be able to see exactly where the leak is.Often is is a hose,not the switch itself.

Posted on Oct 05, 2010


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Hv/a/control on console only comes out center dash

that is called the MODE damper
its like a door inside the heater box.
there are 3 kinds, (cable. /vacuum and motor controlled)
in a shop we find out
1: which kind then test the control to make sure the control works.
2: then make sure the mode damper works (it wont)
3: we then look and see this car has a motor and the motor is dead
3: we replace the motor and the mode damper now works.

the FSM shows the tests here, under HVAC, you can read that
any time, or login to and read that.

if cable , you just watch the cable move. it either does or dont at each end (if fail its obvious why, right>?) jammed or broken cable.

if vacuum, you watch the servo move. if it dont , its bad or the control bad. or the damper is jammmed, i release the link and operate
the door, by hand, it works and i find the servo diaphram leaks
doing a vacuum leak down test, bingo bad servo.

or if electric motor dampers. i do the FSM tests,. no 2 cars
motors work the same, so i'm compelled to RTM read the words
and graphics in the FSM, it shows how to hot wire it and test
ALL angles. if fail the motor is DOA. get a new motor at any toy dealer.
there i have covered all cars made , all 3 systems.
ask questions.

Jan 31, 2014 | 1998 Toyota Camry

1 Answer

94 gmc suburban ac/heater control for front wont respond

try a new control panel from the junk yard-there cheap and that may solve your problem-the last one i replaced i pick up on ebay- cheers Denny

Jan 02, 2014 | GMC Suburban Cars & Trucks

1 Answer

The rear A/C works but the heat does not on my 04 yukon.

Could be the swap valve/damper not opening to allow air to flow thru heater core in rear or control switch not telling it to change.

Oct 30, 2011 | 2004 GMC Yukon

1 Answer

I have a 99 gmc sanoma there is a vacume leak some wears there is a vacume line running throu the driver side finder well and i dont know wear it goes

Have an assistant blow cigarette smoke in the end of the line and look for the leak under the dash,
Thinking that goes either to the brake light switch or the heater control

Sep 16, 2011 | 1999 GMC Sonoma

1 Answer

I have 1999 ford Econoline 250, air conditioning works but the air damper does not open that air to come out of the vents, I have checked all vacuum lines, before it completely shot down, the damper used...

I would be looking again for a vacuum leak. The damper failure on acceleration suggests the vacuum was weak to begin with. Would it be possible to disconnect the vacuum at the manifold and the switch and just jump directly from the manifold to the switch with a new piece of vacuum hose? That would suggest a leak somewhere else in a vacuum line. Also, have you checked the vacuum line from the switch to the damper? Can you get a connector and just bypass the switch (to see f the switch is bad?

May 08, 2017 | 1999 Ford Econoline

2 Answers

Heater blowing hot air

If you have a new heater core inside, some of the probable causes of your lack of hot air include the two heater hoses, heater control cable, water pump, and damper/vacuum door. A handy diagnostic article that explains this will is the following:

Hope this helps!

May 27, 2009 | 1996 Pontiac Grand Am

4 Answers

Climate controls

Car manufacturers use the defrost mode as a default for safety reasons. Being they want you to be able to defrost the windshield no matter what. So when something goes wrong the system automatically goes to the defrost mode. You most likely don't have the vacuum hose connected under the dash at the climate control assy. Or if this vehicle doesn't use the vacuum hose style you may have not plugged in one of the connectors under the dash or behind the climate control assy. Good luck.

May 21, 2009 | 1997 Lincoln Continental

1 Answer

Vent selector inop

U have either lost the vacuum to the mode selector switch (in the dash control) or the vacuum mode selector switch is leaking in the ac/heater control in the dash, u can usually hear a hiss if it is leaking. the vacuum source is the engine, a small hose runs through the firewall on the passenger side to the switch from the eng vacuum source.

May 19, 2009 | 1994 Chevrolet S-10

1 Answer

What year automatic tranmissions will fit a 1995 sanoma

93-94-95 are the tran. that will work with your transmission control module

Dec 09, 2008 | 1995 GMC Sonoma

Not finding what you are looking for?
1994 GMC Sonoma Logo

Related Topics:

190 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

76848 Answers


Level 3 Expert

1311 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22246 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides