The vette I have is a 95.

The problem I am having is with my A/C & Heating. They both work but, it is either hot or it is cold. Meaning any temp I set from 60-85 degrees is cold and 90 is hot.

I am wondering if there is a rheostat that works with the temp adjuster switch on the dash to combine the A/C and heater to give you tempetures for the mid settings. (hope that made since!)

If anyone has a suggestion on this problem please chim in!

C4 friend,
Wilbur

 

Assuming no trouble codes are stored for the HVAC system (do make sure that you don't have a flashing LED on the Dash Controls), you could spend a great deal of time and effort (and money) trying to track this down. System is controlled by a temperature door that adjusts air flow between the heater core and the a/c evaporator. That door is controlled by an electric motor and it's moved by a processor - the Programmer. The Programmer determines the best position for the air mix (door) based on the temperature selected at the dash controls and information from two to three thermistors (depending on model): an inside temp sensor, a sun or load sensor and an outside temp sensor. And any of the components, including the motor itself, could be the problem.

Off hand, my guess would be that it's either the Programmer or the Dash Controls. That's because at 60 and/or 90, the temp door stays at either full cold or full hot - the programming is such that the door doesn't blend anything at these settings, and your Vette simply lacks the inbetween stuff, so it must always be thinking 60 or 90.

The easiest and least costly way to test it is with a bidirectional scanner. The Programmer communicates with the CCM and a scanner, with the right software, can send instructions/commands which should make the Programmer do all sorts of wonderful stuff, including testing it to see if it can move the temp door to a blend position. If it works as commanded, then the Dash Controls are suspect - if not, you probably need a new Programmer.

In short, if you don't have access to a bi directional scanner, fork over whatever the flat rate is at your local dealer for a correct diagnosis - you'll probably come out $$$'s ahead.

 

I've sort of got the same problem (92 LT1) with the A/C/Heater control. There's no message on the dash panel. When I put the temp on 90 I can hear the door moving and the same when I put it on 60. It takes about 5 seconds to move from one end to the other.

But the problem I have is after I turn either the A/C or Heater on for 10 seconds, I can smell something burning so I have to turn it off. I can't figure it out for nothing. Guess I'll have to go see Mr. Bendover.

 

Thank you for you informative reply. Looks like that is what I need to do.

C4 friend,
Wilbur

 

Not much that will create a stink behind the Dash - I'd be more inclined to lift the hood to observe compressor operation. A slipping a/c clutch makes a pretty bad smell and the fresh air inlet can bring it in through the vents. I'd check it cold. Have the a/c off and while you're looking at the compressor, have someone hit the Auto button. If the clutch is slipping, you can usually see it the minute it engages. If it's slipping a lot, you'll smell it under the hood too.

 

I'm deep in a similar problem in my 90 coupe. One thing I've learned is that the temperature door is part of a closed loop system meaning that the programmer knows the position of the temperature door and open/close it in small increments it to maintain the interior temperature.

What Kingcobra54 describes sounds like door position feedback circuit has a fault and the programmer cannot position it properly. If you see one or more flashing buttons on the heater controller the system has detected the fault. You can get the fault code by pressing both Fan up/down buttons at the same time until 00 appears in the display. Then press the center auto button. If you see a 01 or 02 appear in the display then something is wrong with that circuit.

SunCr is 100% correct about having the problem diagnosed. Getting to the programmer and heater door is not easy by any means. It would be nice to know exactly what the problem is before tearing everything apart. Also if you do not have one I'd suggest getting the Helms manual. It has detailed diagrams and diagnostic procedures. It was the best money I ever spent.

My two cents worth..

 

I checked the a/c clutch tonight and it works like normal. It starts spinning when a/c is on and the fan kicks on too. I'm just not getting any blower power when I turn the fan on to 10. 10 might as well be 2. The burning smell is so bad you can't take it past 20 seconds. I just don't have much time to go see the man.

 

Hi rib_lover,

I did not notice any flashing buttons. I went out and check for codes by the procedure you described above. When I held the to fan buttons down until the double 00 showed up. I then pressed the Auto button and a (-) sign shows up in front of the double 00. When I press the fan speed adjusting button I then get a list of numbers. I got lots of numbers and thought I would post them.

The following are the numbers: 01,02,3,04,05,06,07,08,09,10,11,12,16,17 ,19,20,21,22,23,24,30,31,34,35,36,37

Do these numbers make since? Also can I erase all the numbers that are stored. Then I could check daily for any numbers that may pop up.

I see you also recommend getting a manual. I have been looking at the Chev Shop Manual for my 95 vette. Do you recommend the Helms book over the Chevy manual?

C4 friend,
Wilbur

 

"I checked the a/c clutch tonight and it works like normal. It starts spinning when a/c is on and the fan kicks on too. I'm just not getting any blower power when I turn the fan on to 10. 10 might as well be 2. The burning smell is so bad you can't take it past 20 seconds. I just don't have much time to go see the man"

Blower is controlled by a Module mounted on the Evaporator case (engine compartment/firewall/passenger side) which just so happens to be cooled by the air blowing pass the Evaporator Core, which then of course comes out through the vents. Never heard of one having an odor (but they seem to fail with some frequency). It certainly makes sense - along with no blower control - that yours is the cause. Test it first by checking for the signal voltage on the Tan or Brown wire at the Module. It should have about 2.5 volts at "1"; 6 or so at "10". Output to the Blower is Purple. Look for 4 volts at "1"; 12 volts at "10". Check it's power feed too - red - for battery voltage. Same Module is used by GM for all makes, so it should be available at any Dealer or NAPA has a stocking number.

 

King Cobra: If I remember correctly, those numbers are the various modes which contain useless binary info from the Programmer. I think the important/diagnostic mode is "8". I don't have the specific info handy at the moment, but you usually Page up to that number, then down, for any HVAC codes.

 

SunCr, can you PM me your number so I can call you? or if you like you can call me at 850-499-5078 cell.

C4 friend,
Wilbur

 

Is this what I need? If no, what's the name of the part?

http://www.autozone.com/servlet/UiBr...3d8004ac5c.jsp

 

This is the module(for the 90 in question)


It's only held in by three small screws. Pop it out and smell it, or turn on the HVAC system and with the hood open, go over to it and see what happens. Look down into the cavity and see/hear/feel/smell what the blower motor does also.

 

When you pressed "auto" the first time it displayed 00 which means no faults were found. Thats a good thing. When you pressed the up and down buttons it instructed the HVAC controller to ask the CCM/ECM for various parameters. For example if you would have set the display to 2 and pressed auto it would show you the 8 bit analog value of the in-car temperature sensor ( not very useful ). Setting the display to 16 gives you the engine temperature in centigrade ( a little better) . Its all documented in the shop manuals.

You may want to verify the varous sensors are working. you need to verify the in-car temp sensor (2), Outside ambient temp (3) and the sun load sensor (4) All three should be somewhere between 50 and 200. If the number is preceeded by a minus sign add 100 to the value i.e. -130 is really 230.

It my understanding that the GM shop manual is the same as the Helms.

Later....

 

Thanks for your information. If I am understanding your reply I can use the fan up or down buttons to scroll to the number 2 (in-car sensor) then press Auto and to get the value? or is this something that will have to be checked with the Scan tool?

A purchase of a manual is forth coming.

C4 friend,
Wilbur

 

I haven't taken the screws out yet but she smelled a little. I can't find that part in your pic here at the vette store or autozone. What's it called exactly. It's starting to get cold again?

 

It's called the Blower Control Module (listed as Module, Blo Mot Cont on the ac delco site). It's part #15-71642 for the '90 and up.

 

Thats correct.. just use the fan up-down buttons to select the parameter and press auto.. Unfortunetly the HVAC controller can not be used to send a specific command to the programmer. For that you need the scan tool. It would have been nice to have that ability built into the controller.

When you get your shop manuals there is a whole section on the C68 electronic HVAC system with troubleshooting diagrams and loads of information. You should be able to diagnose whats going on. Its a very good manual.

Later...

 

Thanks!!!!!!

C4 Friend,
Wilbur