Tom 35th anniversary

Ive been pouring over the service manual and am getting ready to tear into this , this weekend along with a new heater core but I thought I would ask for any opinions where to start if anyone has had the same condition. 88 coupe.....blower and temp controls all seem to be working .....mode changes to appropriate vents when pressed. I can set it cold and compressor comes on but no cold air only hot......I pulled the heatsink assembly out of blower box and looked in while someone cycled controls for me and I never see the hot/cold damper door swing. My initial reaction is the damper door motor....unless whatever feeds it the signal has went bad.....just looking for some of this forums vast knowledge to possibly keep me from chasing my tail all day.

Thanks in advance

Haggisbash

Hi, sounds like the heater core is fine as long as its not leaking. You are correct, looking down into the heater box you should be able to see the door swing and if its not that is one issue but when you select cold you should get a blast of cold air out of the heat sink assembly hole regardless of what the door is doing at least that is what happens on my '93.

Tom 35th anniversary

You are correct cold air does come out of the hole so I know the cold air is there.....the flap is just not moving.......there is some water in the diverter box.....so i figure time to replace heater core and take care of this heat problem at the same time.....

kenmohr

Mine is doing the same thing. Everything works except the blend door. Had a check up at local shop and they said they was fairly sure it was the head programmer. Possible the blend door motor but less likely. waiting for the season to end, winter project. Mine does change frpm heat to AC from time to time.

Tom 35th anniversary

Yes, I doubt the blend door motor is at fault....I am going to order the repair kit for the head unit and the box with the solenoid units in it under the dash as they both have print boards with electrical components that fail over time with the heat.....It does not look like a hard fix to try and is relatively cheap.(Just some component unsoldering / soldering)

cdm747

I had the same problem. It has been discussed many times. Check the connector between the blend door actuator and the blend door. It is under the dash on the passenger side. There is a plastic clip that holds the two together that has a tendency to break. You can find a replacement clip at any parts store in the "Help" parts. You should be able to see it but will probably have to drop the ECM out to be able to get your hands in to fix it. Do a search and you will find a lot of articles about this.

ctmccloskey

This subject was brought up recently and I remember something about the vacuum source being another potential problem. Good Luck

I have a 1988 Coupe and on my car Bryan Thompson of BATEE.com suggested that I rebuild blender door while I was rebuilding numerous other parts on the dashboard and under it. He would be the best reference if you have questions. He sold me a kit to do the blender door, C68 A/C control head unit and the standard Digital Dashboard Upgrades. I hated to "Fix" something that was not broken but I was there so I did it. I am not really keen on taking the Dashboard apart over and over even though it gets faster each time...

I wish you the very best in solving the issue with your Corvette!

Tom 35th anniversary

Well.....some questions answered !!!! I figured because i need to change out the heater core I might as well pull out my cracked/nasty crash pad and replace it also.....What a pain in the a$$.....Hidden screws/bolts....even with the FSM it wasnt really clear but i got it tore down and looks like i will be able to get at the heater core a little easier. It turns out the heat all the time problem was the little clip on the door motor was broken and the rod came out of the lever.....at least i wont have to chase an electrical problem!!!!!

ctmccloskey

Great Job there Tom! The dash board of the C4 is not an easy item to disassemble. It is a shame that you did all that work just to find the clip that operates the blender door to be broken. I guess that is better than "not knowing" what is causing the problem in the first place. I hate taking half the car apart and having to change out a .25 cent part that GM got "cheap" on when they sourced it originally.

Good luck with your Heater Core replacement. That is something I have not had to change yet. I try to change the coolant every five years (at the max) as this hopefully makes the various components last longer. I also do not run DEXCOOL in any of my GM's any more. I went back to the older style Green A/F.

It sounds like you are in good shape now that you know what happened. I am sure the heater core will be a breeze for you now!

PatzwaldB

I suspect I have the same problem. The heater control valve looks like it is working fine. I get heat for a short period of time when I first start the car but then the heat seems to go away. I think that heater door is flapping uncontrolled in there. I am not sure how big a job it is to replace. The car has a new heater core so I don't need to go that far. It would be nice if it can be replaced my removing the cover and the computer without going too deep. I doubt it is a job I can tackle since I will have visiion problems for the next 6 to 8 months.

Tom 35th anniversary

Well, I finally found some time to put the heater core back in the car. Some success...no leaks (I did pre test for leaks so no surprise). What a pain in the butt getting the heater box half back on and most of the screws back in.....I opted to leave the one on top off as i could not get the screw started no matter what i did. Now for the problems i am seeing now. I replaced the plastic clip on the blend door motor arm and set the rod into clip with the blend door motor at its most advanced heat position. What I am noticing now is when I set to a/c at its coldest position the motor moves and the door swings to its fullest swing the other way but....when it hits physical limit the blend door motor keeps going a little more pushing the clip further down the rod......too much motor travel!!!!.....It looks like the blend door motor goes too far both ways forcing the rod to slide through the clip....this will cause a clip failure again in the near future......Now I am at a loss as to what would cause this???? Any ideas???

Thanks in advance

kenmohr

What all did you have to remove to get to the blend motor?

HAD2HAV2

Do what I did. I took a 1 inch dia.bolt (cut the head off) and had it welded to a nut that will fit the threads of the blend door rod. Doesn't matter if the bolt threads get buggered up during the weld process just not the nut threads. You can then cut the excess threads off. Spin it around the door rod about a 1/4 inch and the then slide the welded bolt threads into the motor. $9 and will never break due to heat.