My dad has a 94 vette (I have a 68) with the c68 electronic automatic air conditioning option. The problem we are having is that the temprature door (mix valve?) will not open to allow cold air from the air conditioning to cool the cabin. We have copies of the GM Service Manuals and have performed the recommended diagnosis.

There are no Diagnostic codes being set and the outcome of our troubleshooting indicates that the HVAC programmer has failed.

We can manually drive the motor for the mix valve by applying + or - 8volts to connector c295 pins b and c. The door will open and close successfully. Our assumption is that the solid state drive circuitry has failed on the programmer board. By tracing the lines back from pins c7 and c8 on the programmer board (16192582 and 16177111) they go back to an 8 pin dual inline IC chip. It has the numbers 519V 3107 9328 and 67968 on the chip. I believe the key number is 519V and the others are manufacturing and/or date codes.

More info - When we look at diagnostic parameter 34 with the air conditioning set to 60 (the air conditioning blows good cold air) the reading is proper at -153. When we look at diagnostic parameter 24, it reads 00. So, this makes sense to us. The programmer is being told the door is closed and the programmer is set to -153 to open the door.

I have seen older threads that discuss replacing the 4 capacitors on the board. This made sense and even though our symtoms were different I replaced all 4 capacitors with no change in behavior.

At this point what options do we have? I have seen used boards from $300 to over $1K on the web and am concerned about their quality. Does anyone have a schematic for this board? Does anyone sell new boards? Does anyone reputable fix or swap the boards. Does anyone know what the 519V IC is? I would like to take a chance on replacing the chip but I have been unable to find the specs for the chip.

Sorry for all questions. Any help or insight would be welcomed. We do not mind getting our hands dirty but, if we have to spend the money we would like to deal with a recommended reputable vendor.

 

I first ask if all the buttons on the control head seem to work correctly. IE. Control fan speed, change vent configuration with air coming out respectively and compressor engaging in recycle, external and defrost modes.

By driving the blend motor as you did does verify the motor is working. But there is also a feedback rheostat that sends a voltage back to the programmer telling the programmer where the door is. If the voltage is wrong, the door will not be driven to the right position. Some other people have had similar problems and replaced the blend motor and fixed the problem - just saying.

Also, if the evaporator box did not drain properly, it can leak back into the motor and cause some problems. This happened to me and I dried it all out and I was OK, (I checked it all out when it was open, careful of the gearing, it all matters.

After being on the Forum for 10 years, and read a lot, my take on the problem is that I not have heard of too many control heads or programmers being the cause of this type of problem. As illogical as it seems the motor was the cure, just saying.

I'm glad you liked my thread on the 4 capacitor replacement, - sorry that one did not help you on this problem.

Check my thread on this as it might give you some insight on this related problem.

https://www.corvetteforum.com/forums...blem-94-a.html

 

I made a schematic for the older style (before 1990) HVAC programmer. I don't have a newer style to trace out. The "smarts" for the HVAC system were moved from the HVAC controller to the HVAC programmer in 1990. 1990 and later HVAC controllers only monitor button presses and display data on the LCD.

The 67968 on the chip is probably GM's abbreviated part numbering scheme for ICs. The real number has 8 digits. It's probably 16067968. The only place I've ever found for GM ICs is a place called Elliott's Car Radio. His web site has gone wacko and no longer works, but you can Google it. He spent years collecting GM ICs and has a huge stock.

 

PColt94 - Thanks for the quick and detailed reply. All the buttons on the control head work fine. I agree it makes more sense that the problem would be mechanical and involve the motor, rheostat or door assembly but, that does not seem to be the case here.

When we drove the motor / door to both its extremes, the resistance readings were both in spec. We also reconnected the C295 connector with the motor / door at both extremes and parameter 24 read 00 and -153 as expected. We also stopped the motor / door in the middle and the reading was between the two extremes as expected. I think the motor / rheostat assembly is working and reporting fine.

I did look at your motor assembly post (well done). We did have the motor assembly apart early in the troubleshooting process and it looked factory fresh inside.

From my experiences also, I agree with you, the programmer would be my last choice to think was the problem. Although, in this case everything points to it. I wish I had a donor programmer to use to verify. I might be able to borrow one out of a friends 92. I know the part numbers are different but, are they functionally equivalent?

If the programmer is bad, what do recommend is my best course of action? Fix, swap, have refurbished or can I buy a new one somewhere? Thanks again to the community for your support.

 

Cliff, Thanks for the information. I will give Elliott's Car Radio a try to see if they can identify the GM IC

 

Reverting back to your initial statement: "The problem we are having is that the temperature door (mix valve?) will not open to allow cold air from the air conditioning to cool the cabin."
So then are you saying that the door is in the position for heat? Did you try removing the motor and flip the door to the other extreme position, then run the A/C and get cold air out of the vents?

I don’t know if you exactly tried this. Externally drive the motor to a mid position. Then reinstall the motor and the electrical. Either watch underneath or the blend door thru the evaporator with the fan module removed. Then, turn key to ON and punch up A/C. The door should move one way or another. If it does not, the programmer is not doing anything. Reason for this is, if the feedback voltage is wrong at one end of one of the limits, the (dumb) programmer might not like the end limit voltage and will not drive it back to the other end.

From what I have seen the 92 programmer is not a replacement for the 94. I do not know the difference. I would at least look at the connector and board to see any apparent difference. To try it is a crap shoot to see if that portion would work to gain any knowledge. Vacuum lines need not be connected, just look at the door physically and run the temp up and down.

 

The number of vacuum solenoids changed over the years, so that might explain any differences from year to year. My '86 HVAC programmer has 6 vacuum solenoids and I know the later ones only have 4.

 

Contact Batee.com. He is very good at diagnosing C4 ac programmers.