HVAC issues on a 1990

[jrd1990zr1]

I posted a while ago, pulled the heater core to get to the actuator since I had no heat only AC. Tried two different actuators, when I switch to heat, temp at 90 degrees the blend door pulses open and closes about a quarter inch. Spoke to Bryan Thompson he thought it might be the programmer. Pulled the programmer, control head and shipped them to BATEE with the actuators.

Bryan tested with my actuators found one with a broken gear but the two others would pulse the door when calling for heat. He tells me it works fine with his actuator so he ships it back and I buy a brand new actuator from AC Delco. Install the parts, power up the car and it pulses when calling for heat. I find no open circuits, but the power to the actuator when calling for heat pulses between 7.6 volts and 0.5 volts. When calling for AC the power remains steady at 7.6 volts. POT input just below 5.0 volts per the FSM. Bryan claims there is nothing wrong with the programmer or control head, but I can not figure out why it pulses when calling for heat. Anyone out there have any ideas?

Thanks in advance and Merry Christmas to all!

[QB93Z]

Please describe what you are observing that you call "pulsing"? What position are you referring to when you say "closes a quarter inch"? ("blocking air flow thru the heater core"? or blocking air flow thru the AC evaporator?)


With the thermostat set at 85 degrees, the blend door should move all the way to block air flow through the AC evaporator coils. In my 1994, the blend door moved smoothly and continuously to its commanded position.


When the ignition is turned ON, the blend door should move full travel in one direction and then full travel in the opposite direction.


The HVAC programmer needs to be reset by disconnecting the battery for 30 seconds after any changes to the system. Have you been doing that?





Jim

[jrd1990zr1]

Jim, responses below in red.

Please describe what you are observing that you call "pulsing"? What position are you referring to when you say "closes a quarter inch"? ("blocking air flow thru the heater core"? or blocking air flow thru the AC evaporator?)
When temperature control is set at 60 degrees, blend door covers heater core. When you raise temperature to 90 degrees the blend door moves about a 1/4 inch then closes back over the heater core. The door continues to pulse open and closed until the temperature control is lowered back to 60 degrees .

With the thermostat set at 85 degrees, the blend door should move all the way to block air flow through the AC evaporator coils. In my 1994, the blend door moved smoothly and continuously to its commanded position.


When the ignition is turned ON, the blend door should move full travel in one direction and then full travel in the opposite direction. The blend door does not cycle at all.


The HVAC programmer needs to be reset by disconnecting the battery for 30 seconds after any changes to the system. Have you been doing that? Yes many times. For the last two days I have left the battery disconnected. When I reconnect the battery and turn the ignition on the door does not move. If I run temperature to 90 degrees the door pulses open and closed as described above, or if the temperature is lowered to 60 degrees it closes tight against the heater core.

Jim

It does not seem like the actuator is recalibrating. I get a code 01 and when I go further into the diagnostic parameters #11 and parameter #12 never match.

Update: spent about 1/2 the day disconnecting and reconnecting the power and trying to get the blend door to calibrate. Tried two different actuators and also the new one. All give the same symptoms. Even tried hooking up the CDM and the blower resistor, thought that might be the problem. Blower works all speeds, and is not locked out at startup calibration like FSM says it should. This leads me to think the problem is lack of calibration. Where does the commands for calibration come from; programmer, control head, other? :censored:

[SBAquaLT5]

Was this ever resolved? I'm having similar issues. Blend door moves full travel and heater hoses are hot.

[jrd1990zr1]

Was this ever resolved? I'm having similar issues. Blend door moves full travel and heater hoses are hot.

Yes (knock wood) I finally got it resolved. In process of putting the car back together. The actuator was bad. Mine is a 1990 so the actuator is on top of the heater box and a PITA to get to. I went thru 4 actuators before I found a good one.

If your car is a 1993 then I think the actuator is on the bottom of the box and easy to get to.

Good luck, I don't want to ever have to do this job again.

[SBAquaLT5]

Thank you for the input. My blend door seems to move fine and hot coolant is flowing, but still get cold ambient air. Might be a different issue. Glad you got yours fixed!

[jrd1990zr1]

Thank you for the input. My blend door seems to move fine and hot coolant is flowing, but still get cold ambient air. Might be a different issue. Glad you got yours fixed!

Are there any lights blinking on the control head, may have a code stored.

[SBAquaLT5]

Are there any lights blinking on the control head, may have a code stored.

None. I'm going to give the system a serious flush. My only thoughts are the flow is restricted but not blocked. The heat seems to have absolutely no presence. 90 deg Heater vent air feels like ambient air.

One thing I'm concerned about is the A/C was rebuilt on it before I got it. I'm not sure what was done and if that would have any impact on the electronic control.