I was investigating a problem where my '89 vette blows only hot air. The temperature control door is suspect but I do not know exactly where this is. The previous helpful response was :

"Assuming the a/c is properly charged, the temperature control door is in the evaporator housing and is linked to a motor located inside the passenger compartment on the heater core housing. The linkage is connected with a plastic piece and it could be loose or broken (more than likely) or the motor could be shot or it isn't getting juice from the a/c programmer (not as likely) To see if the door is functioning, access the evaporator housing by removing the blower control module. The door is to the left as you look towards the rear of the car. Note it's position at full cold. Now select full heat at the dash assembly. The door should have moved. If not, then the problem is in the aforementioned items. To access the motor, you will need to drop the hush panel on the passenger side. The linkage is on top and you should repeat the full cold/full hot test to determine if the motor is working. "

Can someone explain where exactly I could see the flap. I am not sure where the evaporator housing is or what it looks like. Is this under the dash inside the car where the passenger sits?

 

The evaporator housing protrudes from the passenger side firewall and has two aluminum tubes going into it. Looking into the car, you will want to remove the module which is bolted on the right top side of the housing. Inside and on the left is the flap you need to observe.

 

Does it blow hot air all the time?

Anyway to answer your question.. if you drop the black hush panel under the dash on the Passenger side and up fromt he bottom you will see a metal rod protruding from the direction of the firewall.. it connects to a plastic arm on the Temperature Door Motor (assuming you have the C68 auto climate option) this could be the problem.

If you are getting Constant hot air on your feet at all times. it is more then likely the A/C programmer located on the driverside just above the accelerator pedal.

Below is a picture of the Temp Door Motor.. it is in the center of the picture

 

Just a little more info on this problem.

The vents would blow very hot air only nomatter what the temperature was set to or of the A/C was on. It's not an AC problem since the vents would normally blow cooler air if it was set to a low temperature whether or not the A/C is on. The blower/fan is working fine and is adjustable ...but there is enough idle leakage where the car gets uncomfortably warm.

Also - this was intermittent at first where it would blow hot air about once a week for the past couple months. Now it works about once a week.

Thanks for the picture, could you define it a little more specific from all the other stuff under the hush panel.

 

Hey Barrypaul I have the same problem with my heater/ac. I can start the car with temp set to 16 and it blows cold air. Restart the car a bit later and it blows out hot air. Or I don't get cold air at all. This is an intermittent problem, and I can sometimes get cold air out if I turn it on and off several times.

Have you had a chance to take a stab at this yet? If so what did you find, and how hard was it to get to the vent motor? I am going to have to deal with this soon, as it is driving me nuts, just not looking forward to it though.

thanks

 

Before you start to tear the car apart, try simple steps first.

Near your distributor , underneath it is a vacum line with a vacum tee. Check the lines and the "tee" to make sure they are in good condition and are not cracked or broken. Take a good look at the tee for breaks/leaks. Once you are satisfied with the vacum lines then;
Under the dash on the driver's side near the brake pedal is the programmer. It is approx 3x6" and black in color. It has a vacum harness, an electrical connection and is attached to the firewall with one bolt. Remove the programmer (remember that there is also a small bolt in the middle of the vacum harness also). Open the programmer and look at the board. In the upper right corner there are two resistors. Check the area to see if the board is discolored and if the soldier connections are broken or are a dull gray in color. These resistors (2 for .49 in Radio Shack) are the main problem. You can go out and buy a new programmer for $3-400.00 or take it to a TV repair shop to resoldier or replace the resistors. This is the second most common problem to heat-a/c failures with the vacum connection being #1. GM fixed this problem in later years by installing larger resistors to dissipate the heat. When the resistors heat up they either burn themselves out or melt the soldier causing a break or bad connection.

A third problem could be the plastic connector to the actuator rod to the door actuator. Simple to check. Open the hood and on the passenger side is the heating-a/c housing, attached to the firewall. On top of the unit is a silver unit with a set of wires attached, held in place by three bolts. Remove the three bolts and remove the unit. You can now see inside of the heat- a/c unit. You will see a core on one side and a door on the other side (the door swings back an forth covering either the heater or the a/c core). Very carefully use a screwdriver to attempt to move the door. If the door moves easily then the connecter rod is broke. If the door does not move, the rod and connnector is fine.

If you have any other questions, E-mail me.

 

OK, I found the metal rod that extends from the temp control motor into the firewall. When I change the temp from hot to cold the rod doesn't move at all. I don't hear or feel the motor doing anytrhing. I tried to give it some help by moving it with my hand, but it wouldn't budge. Does this suggest that the motor is seized and that's why it wont move? Or is it likely under the hood where the rod connects? Any help would be appreciated...

'89 coupe W/ auto climate control

 

Should I be able to move that connecting rod by hand?

 

You should not be able to move the rod. It is either the motor (chances not) or the programmer, highly likely. Check the resistors in the programmer.

 

Sounds like the A/C Programmer.. get the Service manual and follow the steps for troubleshooting

 

Thanks Everyone,

For the record, Bob was right on the mark - it was the two resistors (120 Ohms at 2 Watts) - on the programmer board. I replaced them with 150 Ohms at 5 Watts and all's well again. The boards were burnt a little but also the solder connection was either loose or completely melted for these connections. Note that the programmer came out easier by only removing the circuit board - just a little back bending work but fairly easy and thanks to the responses - i knew exactly what to do.

This is an amazing Forum and the members should be commended for such detailed explanations for problems which I believe the dealer (let alone myself) would not be solve.

barrypaul

 

I'm glad everything worked out. Thanks for the compliment