Electronic Temp Controls...???

[LannyL81]

I need a couple of kind souls living in a warm climate to check operation of the electronic temp controls for me.

On my car, which has an air distribution problem, with the temp selected to 85 and the outside air at 59, when I select the floor vents my A/C clicks on and short cycles. The short cycle could be due to low Freon...do not know at this time....but is it normal for the A/C to come on when I have selected heat?? I get main air flow from the defrost, some to the floor.

When I selected the dash vents, the A/C stays off and I get air flow from the dash vents after about a minute. Is this normal?

When I select bi-level, both dash and floor the A/C clicks on and main air flow goes back to the defrost outlet with some to the floor.

I have tried a different control head....no change in operation. I then tried a different HVAC programmer and only thing that changed was that I never got air flow from the dash vents at all, only defrost.

WHY is a re-manufactured HVAC programmer $652!! This is the best price I have found so far.....their has to be someone that I can send this to and get it repaired for much cheaper?????? HELP!!!!!!

LannyL81

 

[Ted Krempa]

you might want to tell us which car is acting up..the 81 or 96

 

[LannyL81]

you might want to tell us which car is acting up..the 81 or 96

Okay, its the 96....this is the C4 area isn't it??

 

[aboatguy]

Its up to 56 here so I am going to print your thread and attempt to answer your questions.
I don't know why a re-manufactured HVAC programmer $652, I hope it is because they are extremely reliable and so nobody fixes them!
Mike

 

[aboatguy]

I need a couple of kind souls living in a warm climate to check operation of the electronic temp controls for me.

On my car, which has an air distribution problem, with the temp selected to 85 and the outside air at 59, when I select the floor vents my A/C clicks on and short cycles. The short cycle could be due to low Freon...do not know at this time....but is it normal for the A/C to come on when I have selected heat?? I get main air flow from the defrost, some to the floor. I was on a hilly route and the air temp was from 58-47 degrees. Mostly in the mid 50s I set the temp for 85

With floor selected most of the air was from the floor vents with a noticible amount going to the defrost.

When I selected the dash vents, the A/C stays off and I get air flow from the dash vents after about a minute. Is this normal?
Dash vents came on in under 2 seconds with no air anywhere except dash vents
When I select bi-level, both dash and floor the A/C clicks on and main air flow goes back to the defrost outlet with some to the floor.
Bi-level air from dash vents and floor vents none from defrost

I do not know whether the AC compressor came on or not. However, how can you drive with the heat set at 85? My car was hotter than two drunken coeds with a video camera.

Do you have a FSM(factory service manual)? Section 1C covers the electronic automatic air conditioning system and has a couple of pages covering its operation. If you have the manual have you check the CCM for system faults?


In case you don't have the manual here is aboatguy condensed version of operation section

To sum things up. Bi-level air gos to the floor(heater) and dash (airconditioning ducts) it also states that this setting will bring the temp to the range selected (makes me think that the AC compressor may run in this setting)

Vent (compressor will not run in this setting) will adjust temp to the range selected but cannot cool the interior colder than the outside temp

Heater most air entering the vehicle is forced to the floor with a small amount directed to the defroster. Temp will adjust to the temperature setting selected.(From this description I believe the AC compressor may run}

IMO this is a sophisticated system that has too many sensors providing input to try and troubleshoot without:
1. Patience
2. A little technical troubleshooting experience
3. Good volt, ohm, meter
4. Helms Manual
5. 1/5 of sippin whiskey
6. case of good beer

Section 1C is 25 pages long.

Good luck

Mike

 

[Ted Krempa]

wonder if the dash vent doors are vacuum actuated? if so, maybe there is a vacuum leak somewhere causing the doors to act up ???

 

[aboatguy]

wonder if the dash vent doors are vacuum actuated? if so, maybe there is a vacuum leak somewhere causing the doors to act up ???

I was perusing the manual and there seems to be a vacuum operated subsystem incorporated into HVAC system. Due to the minute delay in the dash vent selection, you may be correct about the vacuum problem. However, this is a complicated system and I would start my troubleshooting with the manual.

 

[LannyL81]

aboutguy: thanks for the help.
I have been through the Service Manual many times...stepped through the trouble charts...and tried several things. I have removed the press-on retainer on the HVAC Programmer and replaced it with a washer and nut, so that connection is tight....no vacuum leak there anyways. When I pull the vacuum connection apart, I have vacuum, so I doubt that I have a leak.

I know this HVAC system is somewhat complex....more so than it needs to be. I have checked all the vacuum motors that control the air flow/direction and all are working...no leaks here either.

Oh and I do not drive with the temp set at 85...I just did that when I was troubleshooting.

If the HVAC Programmer was easy to get out, I would sure like to try a known good part in my car....may be I have something else wrong. I thought when I got the used programmer that it would have solved the problem and its very odd to me that operation was almost the same....only difference was that air come only from the defrost, whereas with the orginal part, I can get air from the dash...it just takes it awhile.

Except for the slow reaction to shutting off the defrost when I select dash...may be mine is operating okay...just not perfect. And at $652 for a re-man module...I will just live with it until I win the PowerBall!!

Thanks again to everyone.
LannyL81

 

[aboatguy]

aboutguy: thanks for the help.
I have been through the Service Manual many times...stepped through the trouble charts...and tried several things. I have removed the press-on retainer on the HVAC Programmer and replaced it with a washer and nut, so that connection is tight....no vacuum leak there anyways. When I pull the vacuum connection apart, I have vacuum, so I doubt that I have a leak.

I know this HVAC system is somewhat complex....more so than it needs to be. I have checked all the vacuum motors that control the air flow/direction and all are working...no leaks here either.

Oh and I do not drive with the temp set at 85...I just did that when I was troubleshooting.

If the HVAC Programmer was easy to get out, I would sure like to try a known good part in my car....may be I have something else wrong. I thought when I got the used programmer that it would have solved the problem and its very odd to me that operation was almost the same....only difference was that air come only from the defrost, whereas with the orginal part, I can get air from the dash...it just takes it awhile.

Except for the slow reaction to shutting off the defrost when I select dash...may be mine is operating okay...just not perfect. And at $652 for a re-man module...I will just live with it until I win the PowerBall!!

Thanks again to everyone.
LannyL81

Lanny,
Your second paragraph is an understatement!

I have read in other threads about guys that overtightened the (vacuum manifold) creating leaks that caused malfunctions. Have you checked all of the HVAC system vacuum lines? Then again you may still have a faulty HVAC controller.

Good luck!

Mike

 

[LannyL81]

Yep, checked all the vacuum connections. I think the HVAC Programmer is defective. I put an extension line between the programmer and the car's vacuum source and with the car running, selected the different air outlets and each time I checked for vacuum coming out of the programmer. Never had vacuum coming out....and I did not wait long enough for it to switch from the defroster vent to the dash vent. I was just checking to see if I had a leaking vacuum connector. But I was holding the vacuum inlet going into the programmer so I know that it was tight and I was able to check that I had vacuum going in....just nothing ever came out.

Blast it....forgot to buy that PowerBall ticket for tonight's drawing.....now how am I going to win the jackpot if I don't even buy a ticket!!!!!! Got to pay for that re-man'ed HVAC Programmer somehow.......

Later,
LannyL81

 

[aboatguy]

looks like you have done the troubleshooting sorry that it looks $$$$ expensive.


MIke

 

[LT4man]

Factory service manual gives all of the diagnostics and troubleshooting for this problem.

Also, check past threads. A lot has been posted about this problem.

Save The Wave!

 

[Chris Kennedy]

Try gmpartsdirect.com for a new programmer---I got a new one for my '89 for $117 or so. Some others are remanufactured only, and you also may want to try Corvette Central, as they have a really good selection.

/s/ Chris Kennedy

 

[G Winter]

With all the vacuum doors, the system takes a lot of volume. Be sure that the check valve in your canister is working. This works likea reservoir,without a reserve in the canister the doors will act very slowly.This is an often overlooked problem.

Glenn

 

[LannyL81]

gmpartsdirect.com has the best price I have found so far for a new HVAC Programmer....$637 shipped, with $113 of that is their shipping and handling fee. Corvette Central did not have one.

I checked the vacuum at the check-valve...did not measure it though. Had what I thought to be enough there. The cruise control works perfectly, and since the vacuum canister is shared between the two systems, I assumed that I did not have a leak.

I have found another used one for $125 and will go ahead and get that one and see what happens.

At this time I have just put the car back together so I can drive it...I will work on it more at a later time.

Thanks all,
LannyL81

 

[theadmiral94]

LannyL81,

it sounds like you've tried everything and maybe narrowed it down to the problem.

However, did you also try disassembling the HVAC control head and cleaning the carbon 'buttons' behind the rubber membrane as well as the contact points on its circuit board?

The reason I ask is one thing I figured out about our 94 (and I presume your 96 as well).

The Electronic HVAC control head isn't just a switch, but a computer in its own right (as evidenced by the limited number of wires connecting it to the HVAC programmer). It sends an electronic digital signal, to the HVAC programmer, based on translated inputs from the depression of the various buttons.

If the buttons are not sending a proper duration/voltage signal because the carbon buttons/circuit board are dirty, it could result in more than just non-operation, it can result in mixed-up or confused signals to the HVAC programmer which might explain the odd results you are experiencing.

Hope this helps...

 

[LannyL81]

However, did you also try disassembling the HVAC control head and cleaning the carbon 'buttons' behind the rubber membrane as well as the contact points on its circuit board?

The reason I ask is one thing I figured out about our 94 (and I presume your 96 as well).

The Electronic HVAC control head isn't just a switch, but a computer in its own right (as evidenced by the limited number of wires connecting it to the HVAC programmer). It sends an electronic digital signal, to the HVAC programmer, based on translated inputs from the depression of the various buttons.

If the buttons are not sending a proper duration/voltage signal because the carbon buttons/circuit board are dirty, it could result in more than just non-operation, it can result in mixed-up or confused signals to the HVAC programmer which might explain the odd results you are experiencing.

Hope this helps...[/quote]

Yeah I know about the head control unit and how it sends out serial data to the programmer. But I tried a different control head and got the same exact operation, so I assumed that the control head is working as it should.
It still may be that the vacuum connector is collapsing and thereby reducing the volume of vacuum which would cause the delay in the vacuum vent door motors moving. Not much I can do about that other than replacing the programmer. I have tried to open up each line connection, but they are quite soft and my effort did not seem to do anything. I did notices that on an earlier programmer design that they each vacuum line connector was alot firmer, but GM changed it for the part number in the 96. I do not know if the previous part number would work or not....to expensive to try.

Oh well....something to just live with I guess.

Later,
LannyL81

 

[Chris Kennedy]

I just replaced the programmer in my '89 for $117 from Gmpartsdirect.com----why are you getting the $600 plus estimate from them? Did the part change? You might double check to see that they are quoting you the RIGHT part. Everything now works perfectly since I replaced the programmer (the temperature door was not moving to the heat function before).

/s/ Chris Kennedy

 

[LannyL81]

I just replaced the programmer in my '89 for $117 from Gmpartsdirect.com----why are you getting the $600 plus estimate from them? Did the part change? You might double check to see that they are quoting you the RIGHT part. Everything now works perfectly since I replaced the programmer (the temperature door was not moving to the heat function before).

/s/ Chris Kennedy

The programmer for the electronic A/C is different from the one you have....lucky me. I am using the part number off the programmer in getting the price from gmpartsdirect.com. I wish it were only $117...

LannyL81

 

[AIRBUS]

The programmer for the electronic A/C is different from the one you have....lucky me. I am using the part number off the programmer in getting the price from gmpartsdirect.com. I wish it were only $117...

LannyL81

Please forgive the hijack here but I'm about to start diassassembling my panel this weekend for a number of reasons.

In working on your 96, did you run across deteriorating foam door seals back in there?

When I pulled my right-seat vents Saturday, there was a cupful of broken up foam seal pressed up against the back of the vent grills that I'm assuming came from the system doors. (I have a 90 "round dash" with electronic air).