HSTT1

I have a 90 coupe with the climate control for a/c. I turn it on auto and hit the fan to 10. It will blow out cold air, then when it wants to, will start to blow out very hot air for about 5 seconds, then back to cold. My dad says it is a gear that has warn out. Where do I get this gear and / or what is the part that is broken? I know it is a 8 hour job to fix, but cold air in the very hot summer is worth it. The controls for the a/c & heater will freeze up and the green light will blink every once in a while, so I know it has a problem. Just would like to have the part before I do the job.

QZRBLU

HS,
You probably should do some more diagnostics before you start throwing parts at it. Do you have any error codes? This will be a good start for the HVAC: http://www.corvetteactioncenter.com/...agnostic+Codes

RLG

see if the control head has any codes. 09 is low on freon.

HSTT1

There are no codes on it. I did a check and this is what it shows.
00-00, 1-64, 2-55, 3-65, 4-136, 5-111, 6-32, 7-00, 9-02, 10-48, 11-00, 12-155, 16-71, 17-128, 19-87, 20-63, 21-146, 22-171, 23-128, 24-128, 30-60, 31-116, 34-153, 35-155, 36-00, 37-07. I just went out and started it up and checked the codes.
I have heard what sounds like a electric motor grinding noise every once in a while, if it is quite in the car.

The freon is good. It is COLD when it is on right. It just cycles through cold then heat, then back to cold, like the flap is moving to check where it is.

QZRBLU

1-64 indicates you are calling for heat, I think.
2-55 is the indoor temp
3-65 is the outdoor temp

Does the operation change at all if you lower the requested temp? I don't recall if you can set the temp to lower than 64.......

This service bulletin may apply:
http://www.corvetteactioncenter.com/...ooling+Control

HSTT1

The first 00 shows that ther are no error codes in the system. It goes from 60 to 90 in the heat range. It did the same thing in the winter. No heat, till it some how just got stuck and I just left it alone and had heat. If it got to hot, I rolled down the window to cool the interior down. I have pull the battery to reset everything and it is still unchanged. My dad says there is a gear that reads where the flap, that goes bad after so many cycles. I think that is the problem, but I have not taken it apart yet to fix the problem.

RLG

there is a blend door motor that seems to fail, I believe there is also a problem with a plastic keeper that holds the rod to the motor and it can break. Check here on the parts forum.

QZRBLU

Here is a thread from May this year:
my 90 did this, take off the fan relay thing on top of your evaporator core box and watch what the blend door is doing. on mine it was like it was shorted out and would cycle from closed to half way open and then when it got half way open it would flutter for awhile then start to close.

A new blend door motor cured the a/c to hot cycling.

http://forums.corvetteforum.com/c4-t...-thoughts.html sounds identical to your problem.

HSTT1

That soulds like it what I have. Where is the hole to check the blend door? Or do I have to still take the dash apart to see it?