AC / Heater / Defrost Vent Problem

147403 Views 38 Replies 19 Participants Last post by Robert l, Nov 18, 2017

imported_Anonymous

Discussion Starter · Apr 25, 2006

I have a 1995 Suburban 1500.
My airflow is stuck in the floor position no matter what setting is switched on the dash vent switch. I can't get defrost or dash vent air to work. Fan settings do work. Also, there is no light coming on when the AC button and/or the recirculating buttons are pushed. All fuses look good. When the AC button is pushed, it doesn't appear to engage the compressor.
What could be happening?
Can't drive around without defrost. Too dangerous.

Thanks!
Chuck

1 - 20 of 39 Posts

G

· #2 · Apr 25, 2006

In most cases the flap that directs your air flow, is controlled by vacuum lines, sometimes it's a cable. You may want to check to see if the vac line is still connected. unfortunately you will probably have to tear the dash down some. 84fiero has a better handle on these issues. Maybe he'll swing by, and add some thoughts.

Of course if you have young children, you could be the victim of the lolipop in the vent, or some other foreign object that got lodged in there.

Sorry either way I think you're going to need to do some exploratory surgery.

Good luck, and keep us posted.

imported_Anonymous

Discussion Starter · #3 · Apr 25, 2006

One other thing...
There is a motor assembly next to the gas pedal and attached to the air handler box which appears to control the linkage for the "flapper" or "baffle". What is it called? Any how, I pulled it off and checked it out and appears to be working fine. Would there be a separate vacuum system?

Thanks

k9cop

· #4 · Jun 9, 2007

Is there any more input on this. Mine will blow out defrost and floor but not the front of the dash. HELP I'm melting!

mitch2264

· #5 · Jun 10, 2007 (Edited by Moderator)

I am not sure

but reading your description I would suspect the heater a/c control assembly. I have read several posts on other sites that pointed to this. Supposedly these tend to malfunction and do weird things. Mine is squirrely too. If system (fan switch) is off and I just have it on vent, the outside air mostly blows at your feet. Sometimes it will come out of the dash vents. If the a/c button is pressed in but fan selector is off the amber a/c light will be on sometimes or just flicker. I checked this part at LMC and it shows the '95 using a control assembly that is unique to just the 95 models. It looks like the same one as the 96 to 99 models.
Good luck! I did find a post where a guy had detailed instructions on how to rebuild this unit using parts from Radio Shack --just soldering in some new resisters, etc.

Reactions: 1

Cableguy

· #6 · Jun 10, 2007

Good advice, Mitch. I don't think your far off. I had to replace same thing in my work van.

k9cop

· #7 · Jun 11, 2007

When I switch to blow out the front it sounds like it wants to switch, but almost like the baffle is stuck inside the dash. I switch to defrost and I can hear the baffle move. It finally blew out of the front of the dash today. Not sure what happened, so I guess I just won't take it off that setting,

.

DSub95

· #8 · Jun 17, 2007

I have similar issues with my 95 Sub. I just bought it and noticed simsilar things like no light on the a/c or recirc buttons and I had no floor or defrost air just dash. I also noticed the a/c compressor was continuously engaged even if the a/c was off. I started looking at fuses and relays and found there was a jumper wire from the a/c relay (under hood) to a and ECM fuse just next to it. When I removed the wire, the compressor stopped. I replaced the relay hoping the $9 part would be the magic fix, but this did not change anything. I figured this was probably an electrical problem in the dash panel So here I am, looking for suggestions/answers. I did fix the "no floor air" problem. I found the harness to the damper by the gas pedal was unplugged. Now I get floor air only on "defrost" and "defrost/floor" but not on just "floor" but never did get defrost air other that the side window defrost vents.???? Another question: is there supposed to be some type of thermostat controller that keeps hot water from flowing through the heater core (front and rear)? This seems to keep my a/c from getting cold enough.

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SonofThunder

· #9 · Jan 2, 2016

mitch2264 said:
I am not sure

but reading your description I would suspect the heater a/c control assembly. I have read several posts on other sites that pointed to this. Supposedly these tend to malfunction and do weird things. Mine is squirrely too. If system (fan switch) is off and I just have it on vent, the outside air mostly blows at your feet. Sometimes it will come out of the dash vents. If the a/c button is pressed in but fan selector is off the amber a/c light will be on sometimes or just flicker. I checked this part at LMC and it shows the '95 using a control assembly that is unique to just the 95 models. It looks like the same one as the 96 to 99 models.
Good luck! I did find a post where a guy had detailed instructions on how to rebuild this unit using parts from Radio Shack --just soldering in some new resisters, etc.

Where is that post about the guy rebuilding this unit?

winterwolf

· #10 · Feb 23, 2016

SonofThunder said:
Where is that post about the guy rebuilding this unit?

Try this,

Daddyjohn

· #11 · May 30, 2016

Yes I am having the same problem, and I figured it is the head control unit as there is a circuit board behind the temp control and vent selector knobs, recirc, and A/C buttons. I purchased a New one and I still have the same issue. I have seen a post from a guy in Sweeden ( I think) rebuilding his by replacing resistors, or transistors. I guess I will try to fix the old one after a trip to RadioShack! I guess I was fortunate enough to get a defective on new out of the box!

RayVoy

· #12 · May 30, 2016

I doubt very much that your new out of the box unit has the very same defective circuit as the original in your dash.
Usually when this happens, we consider the problem to be somewhere else.
Instead of saying "I have the same problem" on a 10 year old thread, tell us your symtoms and we'll see what advice can be offered.

And maybe a MOD will split this into a new thread.

Daddyjohn

· #13 · May 30, 2016

RayVoy said:
I doubt very much that your new out of the box unit has the very same defective circuit as the original in your dash.
Usually when this happens, we consider the problem to be somewhere else.
Instead of saying "I have the same problem" on a 10 year old thread, tell us your symtoms and we'll see what advice can be offered.

And maybe a MOD will split this into a new thread.

Sorry Ray, I am new to the forum thing, but the symptoms are listed in my post. I have checked everything I could think of fuses, relays, compressor, pressure switches, low and high side ETC. and I am sure you have had the luck of most people of buying a defective part new in the box at least once. But once I figure out how to start a new thread I will try that.

RayVoy

· #14 · May 30, 2016

John, @Daddyjohn not to worry, wasn't finding fault, just trying to help. Welcome to the club by the way.
All I was suggesting, is to give us a list of your problems and we'll (the members) will to help.
I've spent my life fixing things (mechanical, electrical and software), very seldom does a new part exhibit the same problems as the part being replaced. That's why I said, if you have the same problem after replacing a part, that part is not the problem, it is else where.

Reactions: 2

gprice73

· #15 · Aug 1, 2016

This may be of some help. Here are two different potential fixes to problems I've been having, sounds very similar to what is happening here. Late post to this thread but better late than never right??

http://www.chevytalk.org/fusionbb/showtopic.php?tid/27558/tp/1/

http://www.silveradosierra.com/how-...k-series-trucks-hvac-control-unit-t77522.html

First post FTW

Reactions: 2

99BurbanVortec350

· #16 · Aug 15, 2016

Hello to ALL members. I'm new here to this forum. I just created my account today after trying to research a problem I started to have today out of the blue with my '99 Chevy Suburban K1500. I was driving on our way to the lake on this hot day and after NEVER having a problem with my brand new AC system, and components I smelled a burning type of plastic smell with the front and rear air conditioning on. Afterwards my AC light and Recirculation light would not come on. Whenever I pressed either or of those buttons the air flow would switch to floor ONLY, and the strangest part was that when those buttons were not pressed, the air would flow wherever I selected it. I'm leaning towards the actual AC/Heater selector module having burned out. I've checked every fuse available for the blower, and AC no avail. I've seen there are a few things electrically that may be worth a look also under the driver's side has pedal, and on the blower motor. Does anyone have any suggestions please, and thank you?

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MagRce1

· #17 · Apr 25, 2017

4

gprice73 said:
This may be of some help. Here are two different potential fixes to problems I've been having, sounds very similar to what is happening here. Late post to this thread but better late than never right??

http://www.chevytalk.org/fusionbb/showtopic.php?tid/27558/tp/1/

http://www.silveradosierra.com/how-...k-series-trucks-hvac-control-unit-t77522.html

First post FTW

I had this same problem on 1997 k1500. The A/C button and air flow selector did not work. After replacing the AC controle Module, ($200 AutoZone) i found that the A/C button and air flow selector only worked when blower speed switch in "off" position. Based on the second link in your post "Problem #1:
If:
a) air flow is always directed to the floor, regardless of the position of the Mode dial and,
b) the AC button does not illuminate when depressed and,
c) the Recirc button does not illuminate, and the resirc door does not operate and,
d) the AC compressor does not come on;
This is caused by an open Switched +12V power transistor, or it could possibly be caused by a defective blower speed switch."

i concluded that the switch was bad from AutoZone so i replaced it again. No change

The manufacture wires the switches wrong. I checked 3 different units from AutoZone.

i was able to move a wire in the blower speed selector wiring harness and give the A/C button and air flow selector power when ever the ignition is on.

see photos for more. Take the blower speed switch wiring harness off of the switch and remove the 2 blue wire keepers. remove the Green wire in terminal "D". replace it into terminal "E". (Here i had to replace the entire pigtail because some of the wires were burnt and the plastic broke apart.) To confirm, you now want the Green wire (that goes directly to the other plug into the back of the AC Controle Module) to be connected to the terminal immediately below the one that it came off of. This is the only terminal that is visible connected to another "G" inside the switch.

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Alice Lettries

· #18 · Jul 8, 2017

Please help my AC only blows out of the defrost vent I have checked all the fuses and everything I just don't know where to go from there any help would be greatly appreciated thank you

RayVoy

· #19 · Jul 8, 2017

Alice.....we need your vehicle info

MagRce1

· #20 · Jul 10, 2017

MagRce1 said:
I had this same problem on 1997 k1500. The A/C button and air flow selector did not work. After replacing the AC controle Module, ($200 AutoZone) i found that the A/C button and air flow selector only worked when blower speed switch in "off" position. Based on the second link in your post "Problem #1:
If:
a) air flow is always directed to the floor, regardless of the position of the Mode dial and,
b) the AC button does not illuminate when depressed and,
c) the Recirc button does not illuminate, and the resirc door does not operate and,
d) the AC compressor does not come on;
This is caused by an open Switched +12V power transistor, or it could possibly be caused by a defective blower speed switch."

i concluded that the switch was bad from AutoZone so i replaced it again. No change

The manufacture wires the switches wrong. I checked 3 different units from AutoZone.

i was able to move a wire in the blower speed selector wiring harness and give the A/C button and air flow selector power when ever the ignition is on.

see photos for more. Take the blower speed switch wiring harness off of the switch and remove the 2 blue wire keepers. remove the Green wire in terminal "D". replace it into terminal "E". (Here i had to replace the entire pigtail because some of the wires were burnt and the plastic broke apart.) To confirm, you now want the Green wire (that goes directly to the other plug into the back of the AC Controle Module) to be connected to the terminal immediately below the one that it came off of. This is the only terminal that is visible connected to another "G" inside the switch. View attachment 96898 View attachment 96906 View attachment 96898 View attachment 96906 View attachment 96914 View attachment 96922

UPDATE: After the above fix, the controller failed 3 weeks later. I purchased another (3rd try) control module and rewired again back to OEM. and now all works good.

I had 2 bad controllers from the factory. Good luck all!

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