Just ck fuse ok the only fuse not working with test light is first one forth row

 

That fuse only has voltage on it when the key is turned to ON.
It provides power to the Central Control Module when running the engine.

Fuse block.

 

Thanks for the photo are fuse boxes are different I only have five rows yours is nine .my car is a 1992 must have changed a lot in two years.

 

Don't know if this will help but it might be closer to yours.
you need a guy with an 92 book for more accurate documentation.

 

The HVAC programmer RECEIVES signals from the HVAC control head. It NEVER sends any signals to the control head.

Your problems are in the control head or related wiring. Can you get it into diagnostic mode? Try this link:

http://forums.corvetteforum.com/c4-t...stic-mode.html

[ EDIT ] This was true for the 1989 and earlier HVAC systems. The system was redesigned for 1990 and newer cars. [ /EDIT ]

 

Not sure this is correct about signals fed back to the control head. I know it's a 92 but if it is anything like a 94, all sensors feed back to the programmer. There are 2 data lines between the head and programmer. For example, the outside air temperature connects to the programmer and the data is sent to the control head for display. The diagnostics mode sends the positions of vents and motors all feed back to the programmer and get displayed on the head.

There is definitely a loop of data to be completed or a hand shake between the two. That's why if the programmer is dead or disabled be removing power to it (fuse 43 in a 94), there are no LED green lights lit or any action on the controller head. It is not a stand alone item which just requires 12 volts to operate. (Got to be different than a 86).

Just saying

 

He needs an FSM...

 

I'm pretty sure the two work as a pair and exchange data between themselves. I have a 96' so I'm not positive but I think the two models are similar in this respect. I also think a set of 92' FSM's would make this so easy to diagnose. It would give you step by step procedure for troubleshooting this problem. Without it you are just guessing and throwing money at it. The price of a set would easily pay for themselves with just this situation.

As an example the FSM for my 96' states that if the Control Head and the Programmer lose communications with each other the Control Head Displays a single line "----" and goes to a default defrost vent position. It also states that you should be able to press the Fan Up and Down Buttons at the same time for several seconds and then it will enter diagnostic mode displaying "00". Pressing the Fan Auto button will then step through any faults it is experiencing which you would then compare to a list in the FSM to find the cause.

Pcolt94 is correct. There are two bi directional serial communication lines between the Programmer and the Control Head labeled "E" and "C". Entertainment Link and Comfort Link. Data is transfered/exchanged both ways between the units.

 

My post was based on the earlier version of the HVAC programmer, which is one direction only.

Things changed a lot in 1990, so it looks like I was wrong again… I guess that proves the old saying, "a little knowledge is a dangerous thing".

 

Thank all you guys for your help I think I going to buy the fsm. I will post the repair after I fix it thanks again.

 

Cliff - Nobody knows it all, we sometimes say stuff that's wrong but part of the learning curve. That why we are in the Forum. I have also but owe up to it like you. But definitely pick up a lot of good information from you on the older C4s.

Ron - This should help you at least get a start till you get you FSM which may take a while. Should have maybe done this sooner. Its not a 92 drawing but for a 94. Should be pretty close, better than nothing.

My opinion. You have a problem that I usually don't see or hear about which I think I a bit unique. I never heard of a programmer being totally dead causing this symptom but not impossible. Since it never worked when you got the car, I would keep a wide open mind out for man made problem rather than a part failure. (Just a thought).

My approach to the problem would be to try a programmer. That way it will be fixed or know the problem is not there. (Easer said than done as you do not have one on your back pocket).

If you do get one to try, when you unbolt it , it will still be hanging by the vacuum lines (they don't just pull off). You can keep them connected and just switch over the electrical connector for an initial test. Good luck.

 

This diagram definitely shows two Data links... for a 94 anyhow! I'm not familiar with an HVAC Data link set up, it may be nothing more then multistring connection, and this is were the FSM comes to play.

 

I dont know if there is enough stuff working on your climate control to do this, but this might be helpful!

 

As I return to this thread, it was to gain information for myself as my HVAC C68 system has developed a major problem. It was disappointing to not see a completed thread to see what his resolution was.

My symptoms were different but I felt similar and thought the end of thread might help.

One minute all was working OK, then it just developed a mind of its own doing different things. Sometimes one led was lit, or not at all and no control at all. Doing a fuse 18 and 43 head and programmer reset all would look OK till I hit any button and it just locked up. Sometimes just dashes across the screen, no control, you get the idea

Pulled the control head cause it's easy to get out. Just on principal clean all the buttons, pins for board interconnect and a little soldering. Put it back in and was just the same.

While messing around with the fuses and evaluating the whole situation, all started to work again 100%, - days end OK. Then today was back to the problems. My gut said it was probably the programmer so I pulled it. Checked the pin connections and some routine stuff. I thought it was bad so I located a part near me for pick up on Monday.

In the mean time took the board in the house just to see what I can see. As I stared at it I saw the 4 electrolytic capacitors. Kind of reminded me fixing the Bose amplifier boards. So I got out my capacitance checker and checked them all. They were all low by about 50% (would still work) but one was 4 mfd on a 39 mfd capacitor. That’s just too far out of spec for me (it could work depending on circuit but…) so decided to install one temporary that was close to value.

Put it in the car and it all worked first time not problems. Put the old part in, no work. Put the new cap in all is good. So I think I'm on to something, not a hard fix if you have some skills. I believe each capacitor if bad will give different symptoms as Roncap has.

I think a lot of these boards are failing due to age and their not semiconductor related problems.

I am going to start my own thread on the repair with the details and pictures as soon as I get my own car completely fixed. My plan is to get the correct capacitors and replace them. I am going to also buy the new programmer just to have a spare since I got a good price on it.

Wondering if Roncap ever changed his programmer or fixed it.

 

Hope you follow up on this. It is some real interesting information. Thanks for everything so far! jim

 

My recollection from pictures I've seen is that these capacitors are associated with the power supply section. If that is true then you need to make sure to use low ESR (Equivalent Series Resistance) capacitors or they will overheat and fail with time.

 

This is my thread on the repair. It's a recap plus the additional information and details of what I did and found.

Like anything, after you find and fix the problem, it all seems so simple.

http://forums.corvetteforum.com/c4-t...-repaired.html