Long-time lurker, first-time poster. I've found the guides on here helpful in the past when I needed to replace my odometer gears and rebuild my front power window motors.
At the moment, I'm a bit puzzled about what exactly is wrong with the climate control system in my 1990 Grand Marquis. For several years now, the car has had AC which works perfectly fine, but no heat. I can move the ATC temperature selector on the dash all the way up to 85, and it stays just as cold as at 65. I used to hear a faint hiss and then a click when I moved the selector from one extreme to the other -- which I thought was the sound of the blend door actuator moving the blend door. I no longer hear that when I move the selector.
So, I thought this was an open-and-shut case of the blend door actuator malfunctioning. Everything I read up on suggested the small gear inside the BDA unit is what almost always fails, so I bought the replacement gear, followed one of the helpful guides on here to take apart the dash for a 90-91 model, removed the BDA unit, opened it up, and... all the gears look perfect. I moved the metal gear which extends from the actuator itself with my finger to ensure that the plastic gears and the actuator arm would turn all the way from one side to the other and then back. They did.
So I guess this means there are a few remaining possibilities:
1. The actuator itself has somehow malfunctioned and no longer spins, in which case I suppose I should buy an all-new BDA unit.
2. The heater core is not working properly.
3. The in-car temperature sensor is not working properly and constantly thinks it's like 100+ degrees in the car at all times, so the heat is never activated.
(Let me know if there's another one I'm overlooking.)
Any thoughts on which of these is most plausible? Or any suggestions on how I should diagnose which of these is the culprit (without having to reassemble everything first)?
Thanks for any comments!
Edit: I should mention there was a period of a couple years when the heater "sort of" worked. It seemed like, on some occasions, when I switched the selector from 65 to 85, I could get it to switch into heat and, on other occasions, I couldn't. But once I got it to switch, it stayed on heat. This situation was also what initially caused me to believe it was something with the BDA; these symptoms seemed (to me) more consistent with a gear deteriorating than something about the temperature sensor or the heater core.
At the moment, I'm a bit puzzled about what exactly is wrong with the climate control system in my 1990 Grand Marquis. For several years now, the car has had AC which works perfectly fine, but no heat. I can move the ATC temperature selector on the dash all the way up to 85, and it stays just as cold as at 65. I used to hear a faint hiss and then a click when I moved the selector from one extreme to the other -- which I thought was the sound of the blend door actuator moving the blend door. I no longer hear that when I move the selector.
So, I thought this was an open-and-shut case of the blend door actuator malfunctioning. Everything I read up on suggested the small gear inside the BDA unit is what almost always fails, so I bought the replacement gear, followed one of the helpful guides on here to take apart the dash for a 90-91 model, removed the BDA unit, opened it up, and... all the gears look perfect. I moved the metal gear which extends from the actuator itself with my finger to ensure that the plastic gears and the actuator arm would turn all the way from one side to the other and then back. They did.
So I guess this means there are a few remaining possibilities:
1. The actuator itself has somehow malfunctioned and no longer spins, in which case I suppose I should buy an all-new BDA unit.
2. The heater core is not working properly.
3. The in-car temperature sensor is not working properly and constantly thinks it's like 100+ degrees in the car at all times, so the heat is never activated.
(Let me know if there's another one I'm overlooking.)
Any thoughts on which of these is most plausible? Or any suggestions on how I should diagnose which of these is the culprit (without having to reassemble everything first)?
Thanks for any comments!
Edit: I should mention there was a period of a couple years when the heater "sort of" worked. It seemed like, on some occasions, when I switched the selector from 65 to 85, I could get it to switch into heat and, on other occasions, I couldn't. But once I got it to switch, it stayed on heat. This situation was also what initially caused me to believe it was something with the BDA; these symptoms seemed (to me) more consistent with a gear deteriorating than something about the temperature sensor or the heater core.
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