Blown 79

Ok all knowing members, I've looked up all the post I could find and am still trying to figure out what is going on. I just bought a 96 and the AC blows cold then hot then cold again over and over. First it was only blowing out of the defrost and floor. I found a vac leak on the AC programmer, fixed that, vents all work properly now, but it cycles between hot and cold. Also when in auto mode with the fan on auto it never kicks up to high. I can't catch the compressor cycling on an off, the clutch stays engaged. Cabin temp probe? The outside temp reading seems to be reading properly. Help I'm baking.

jv9999

The compressor needs to cycle to keep the evaporator from freezing up. My first thought would be that either the cycle switch is bad or it's low on refrigerant which is causing the evaporator to freeze.

Blown 79

Where is the cycle switch? If the evaporator is freezing up wouldn't it take several minutes to thaw. The cold - hot cycle time is maybe 1to2 minutes. When it blows cold it is very cold.

R59

Sounds like the temp door is changing from heat to A/C you can see it if you remove the top of the fan enclosure.

Blown 79

That's what it feels like. I'll check that in the morning but if so what would cause that?

Churchkey

Freon is probably low suggest having the system pressure tested.

The low pressure switch may have been jumped/bypassed causing the compressor to run constantly.

Blown 79

I'll check the pressure switch too, thanks.

R59

There is a nylon connector on the door arm that positions the door to heat or cool settings, My 96 did this, changed the nylon part and solved the problem.

At first I just stopped the door with a screw driver on the cold side, until I replaced the part.

You can hear the door move with the key on engine not running with the A/C on under the dash passenger side.

There is a vacuum dist. valve that the nipples get soft and close up making the door malfunction and creating all kinds of havoc! Check that valve!!

It's been a while, but you can search this and find it. I hope this helps....

Cliff Harris

The blend door is controlled by an electric motor so vacuum does not matter in this case.

The nipples in question are described in this post (see the rest of the thread for more info):

https://www.corvetteforum.com/forums...post1580705187

Blown 79

Pulled the lower dash and you are correct, the blend door is electric. It is randomly opening and closing. What controls this? There is what appears to be a diode mounted between the vents on the passenger side, is this the cabin temp probe? Could this be the problem? I temporally unplugged the blend door motor.

Cliff Harris

The blend door motor is controlled by the HVAC programmer. I'm not sure where the HVAC programmer is on a '96. On earlier years it was mounted to a bracket on the firewall above the gas pedal. I think it's still in the same general area.

The blend door position is determined by the difference in temperature between what is set on the HVAC control head and the cabin temperature.

Run the HVAC diagnostics to see what is happening:

Blown 79

Thanks Cliff, I ran the diagnostics and came up with no error codes. I'll pull the programmer this week and post what I find.

Cliff Harris

One of the parameters you can look at on the HVAC control head is the blend door position. You could monitor that and see if it's changing.

Blown 79

I'll check it this weekend. It seems like everything keeps pointing toward the programmer, bummer, it's a one year only discontinued item. I looked several places today and can't find one anywhere.

Eric 1988

Blown 79
Did you get this solved? Mine has error code 2 intermittently which says in service manual "indicates the temperature door is exceeding the max hot position." Since mine is intermittent I am trying connection points in the circuit. It is 50 degrees here so I am trying to run hot. Just bought 1996 conv. 6 speed 43000 miles. Found work around is to set to 90 degrees opens temperature door all the way regardless of circuit problem. For those trying to run ac in hot weather you can set at very lowest setting ithink 60 degrees it will move temperature door to full ac regardless of circuit problem. Nice to have override until I figure out problem.