So I'm having a hard time with the blend door on my 90 c4. The blend door has a tendency to fluctuate and won't hold a temperature. I have gotten the flash on my control unit and attempted to pull codes with no luck it always comes up with no codes. I can watch the door fluctuate from the top of the evaporator core housing. I've been trying to access the door all day with no luck, I'm having a very hard time finding resources on how to get to it. It seems that most threads are on the old 84-89 blend door and 93-96 was different as well. I've found that 90-92 used this system and it sounds like it's inside the box assembly. I have bought a choke cable kit and don't mind using that in place of the motor but if I can fix the motor assembly that would be even better yet. Right now though I'm just looking for any help to gain access to that dreaded motor. Thanks in advance.

 

The AC/heater programmer (located above the gas pedal) is the brains of the C68 climate control. Question for you, is the blend door still attached to the rod that goes to the motor? See if the door moves freely. I had a problem with my 88 programmer. Blend door closed off the heater core when adjusting the temperature down when using the AC. Trying to adjust the temperature up for heat, 75 and up, I had a long time delay before the door would move. Finally the door would not move to let heat in at all. Look up BATEE.com. They fixed my programmer so no cable needed. Blend door motor can be fixed also. The motor is deep inside the passenger side dash.

 

The door moves freely that was the first thing I made sure of. I removed the piece with the electrical connectors that bolts to the top of the heater box in the engine bay. Don't know if it's just a fan resistor or a temp sensor or... But regardless I can see the blend door moving. When I adjust the temperature it first moves in the direction of the desired temp, if it doesn't make it all the way it will stop in the middle and fluctuate back and forth if it does make it it will only seal for a moment then lift back up and start ocilating in the middle of the box. I'll check out that website now, thanks!

 

Looks like a AC programmer problem so no need to go after the blend door motor. The AC programmer is not fun to take off. Let us know if you need to pull the programmer off.

 

The system was redesigned in 1990 and there is no blend door rod. The blend door motor gear assembly attaches directly to the blend door hinge shaft.

 

Cliff, is the OP's problem most likely the programmer?

 

Looks like I should shift my focus to the programmer then. I read up on the batee website about repairing the programmer, basically I just need to freshen up any bad solder joints. I'll be pulling the programmer soon. It looks like I need to pull the panel under the steering wheel and it should be easy from there. Thanks for the help so far. I have minimal experience diagnosing electronic climate control problems.

 

Photos of my 88 programmer and tools you might need to remove. Go to ebay motors to see what a 90 unit looks like.

 

I've already located the programmer just a matter of pulling it. Thank goodness it's not as hard to access as the actuator. Should be a good starting point.

 

Keep us informed.

 

So I got the programmer out from under the dash, I opened it up planning to repair any bad solder joints based on the batee website. Although my programmer is completely different than the c68 programmer on the batee website. I also noticed that the head unit on the batee website under c68 is different than mine as well. I had assumed I had the c68 climate control system but everything shown on the batee website looks to be for the 84-89 electronic climate controls, not my 90. So I'm kinda not sure where to go from here. I found a couple solder joints that look a little dark around the edges on my board but nothing very drastic it's hardly noticeable. I'm assuming I should just resolder those joints and hope for the best?

 

Just visited both ebay motors and batee.com. Ebay motors has a picture of the 90 AC programmer. See if this compares to the box you pulled. Batee.com does do work on the 90 dash cluster and AC programmer. Look under Services. Give Bryon an email and discuss your problem. When I had HAVC problems, I sent him my C68 control unit, programmer, and blend door motor because I had no idea what was wrong with my system.

 

I'll send Brian An email. Right now though I'm leaning more towards the idea of wiring a switch into the actuator motor so I can manually adjust it by reversing polarity then wiring in my own independent a/c clutch switch. I really don't like the stock climate system and the way it adjusts the blend door and cycles the ac compressor to maintain a specific temp. I want control over the blend door and the clutch on the compressor. What would really be phenomenal is if someone had a wiring diagram of the a/c clutch wiring harness, the fan relay wiring and how the a/c turns it on, and a diagram of the actuator motor and the voltage the motor runs off of?

 

There's always the Electrical factory service manual.

 

I just ordered the factory service manuals for it. I tried a Chilton manual but it proved to be completely useless. I got the blend door to work by clipping the door position reference wire. I also took a reading on the reference wire which was consistently reading 4.5v with the door and temp setting at 60° but once I switched it to 90° my reference would drop to 2.2 then fluctuate from that to 4.5 to 0. It looks like my problem is actually the reference wire in the actuator motor sending a screwy signal which my programmer is seeing and not knowing how to handle. For documentive purposes for anyone reading this in the future when you remove the glove box on a 90 model vette. The actuator harness is on top of the ducting, it's grey. There are five wires. Black is ground, red is 4.8v being sent as a high reference, blue is the reference being returned to the programmer to indicate door position, yellow and tan are 7.5v which are switched by the programmer to reverse polarity and move the motor in one direction or the other. Now the question is if I leave the motor in and leave the reference clipped will the motor be constantly running due to the programmer not knowing it's already in the hot or cold position. Plus if I do leave it like this I will have to live with occasional blinking lights indicating a code in the system. I don't want to replace the actuator due to the huge task at hand, plus it still works to move the door.

Edit: I can actually answer my own question there, I know the motor runs too long without the reference wire telling it when to stop although it does eventually stop. The question is could it be harmful. Right now I'm just considering my options as far as keep the head as the temp control or adding my own switch.

 

With the reference wire clipped the system will move the blend door to one extreme (hot or cold) and keep trying to move it there. I would think the motor would run continuously and that will probably cause problems eventually.

 

I should have mentioned it does eventually stop. I can hear it.

 

Sorry, you guys are over my head now. I deal with Chemicals in my alternate life.
I thought the first gen C68's were bad at fixing. It seems the components for the 90's C68 are much easier to get at. Hope you get you system working correctly.

 

Haha no worries thanks for the help! The actuator is the worst. You almost have to pull the dash to get it out, however the harness for it is right on top. I'm just going to leave the reference clipped since it still works to go from hot to cold. I'll put up with the code in the system and if the motor ever craps out I'll replace it then.

 

Be careful on your 90's parts, they are slowly becoming extinct. I’m the proud owner of 2 working AC programmers for my 88. Batee told me the blend door motors can be repaired.