02 sonoma hvac issues

Can anyone tell me why my heat/ac only works on #4 is it the blower motor resistor? and why when I switch the mode selector switch air mostly blows out of the face vents ? I looked at the vacuum lines and I do have good vacuum from the black one on the back of the switch but when idling there is a hiss noise from the switch. I took it apart stretched the spring and lubed the rubber it still hisses do I need a new switch ? also everything behind glove box works i think when I turn the selector switch to max ac the door opens on the firewall and on every other mode the actuator on the left(inside glovebox)moves in and out,I even went as far as to split the ductwork by taking out two gold screws and prying it open a little to see if the actual door inside is moving and it is. Is it just that the switch is losing vacuum and not fully changing the modes or is it that because I am testing all this with my fan on #4 and with the vacuum leak it seems more drastic because the modes do change but no matter what air still comes out the face vents.

when you took it apart did you see and oil on the back of the hvac control head?because I did alot of these at the dealer in early 2000.found a bulletin for this.Subject:HVAC Mode Switch Inoperative or Stuck in Vent Mode, Oil in HVAC Control Head and/or Vacuum Lines (Replace Transfer Case Vacuum Switch and Contaminated HVAC Components) #03-01-38-009 - (06/25/2003)

Models:2001-2003 Chevrolet Blazer, S10
2001-2003 GMC Sonoma
2001 GMC Envoy, Jimmy
2001-2003 GMC Jimmy (Export Canada Only)
with 4WD and Two-Speed Electric Shift Transfer Case (RPO NP1)


<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350749&pubid=279#ss1-1350749">Condition

Some customers may comment that the HVAC mode switch may be inoperative or stuck in the vent mode. After some diagnosis, oil in the HVAC control head and/or vacuum lines may be found.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350749&pubid=279#ss2-1350749">Cause

When the transmission or transfer case heat up, the oil may expand and find its way into the transfer case vacuum switch. This oil expulsion may cause the vacuum switch seal to fail and allow transfer case oil to be drawn into the HVAC vacuum lines.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350749&pubid=279#ss3-1350749">Correction

Replace the transfer case vacuum switch. Refer to the Transfer Case Vacuum Switch Replacement procedure in the Transfer Case sub-section of the Service Manual. Also, replace all contaminated parts in the HVAC system.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1350749&pubid=279#ss4-1350749">Parts Information

Part Number
Description
15664811
Switch -Transfer Case Vacuum
the t-case switch is on top of the transfer case.also if there is oil at the back of the control head you will have to replace that also.the oil gets inside the hvac control head,thats why it does not work.plus the vacuum pods on all the doors get filled with oil.might want to check them too.let me know what you find.hope this info helps.

Thanks for your reply, No I dont think there was oil in the rubber inside the switch but there was grease I think some one before me might have tried to repair it as I did and thats how it got there.Today I installed a used control panel from the junkyard and that stopped the vac leak (hissing noise) but air is still slowly blowing from the face vents no matter what mode (floor,defrost etc..) and I also swapped the resistor in the blower motor and that solved my fan speed problems.

you might want to check each vacuum pod under the dash for oil contamination.if so replace them and it will solve your mode switching problem.

Thanks I will check that tomorrow but could it be that the default position is for the face and defrost and im just buggin out because as I had said that I split the duct work and looked at the actual door that does the mode switching and it is moving properly I assume, but it has holes to let air flow thru no matter what position it is in?

check this out to diagnose your blower motor problems http://www.automotiveforums.com/vbulletin/private.php?do=showpm&pmid=762261