Earlier this year I had a problem with my Climate Control only blowing out of the Defroster and Floor registers no matter where you set the air to come from. After a couple of months it started coming out the dash only no matter where you set it once again. Now I can't set it so that I can get the defroster on. I find it confusing that it reversed the problem. I'm looking for someone who has experience and have come across this problem to guide me as to what my be the cause.

Air out the defost and floor vents regardless of where you are directing it to go is the failure mode for the HVAC control unit. Don't know why it reversed itself.

I believe my HVAC is doing the same it hasn't been warm enough plus 43 to test it though.lol But it does the defrost an floor. auto runs once then wont restart on its own. among other things like controlling the temp. only hot. I have no codes anywhere. I may have more trouble then just the controller, gonna start with that.
My question is about replacing it with one out of a junker is a crap shoot I have seen on sites that you send them yours and they will rebuild it, New ones the prices vary greatly, I plan on keeping this 97 Ultra for a while.
Now what is the word on rebuilds anyone have dealings there or steer me in a good direction, prefer a new one, cheap one of course, but 40 bucks to rebuild one? Reliable known place of business?
Well Blane lets see what we can learn. I'll be askin about gettin the dash pieces off with out breaking anything,? lol

I have a buick park ave 1995. I also had this problem. the Hvac unit is nothing more the relays that control the position of the doors inside of the air duct. The doors are not controlled electrically, they are controlled with vacuum. the relays inside of this HVAC unit control the vacuum to the doors. With that said you either have a leak in the vacuum line or the diaphram that moves the door, or the relay is not opening.

I do have a factory manual for an 91 park avenue wich would be very similar, I can make a copy of the diagram for you if this would help.

Thanks But there is a difference between the 95 and the 97. 97 went to all electric? anyway upon hooking the battery up I can hear what sounds like everything cycling through, a system test? So with that an no codes coming up its the hvac controller that is not sending out the rite signals to open an close the needed doors is the way it was explained to me .lol its brain is fried. mine will be here tomorrow and I will see if it fixes the program of set an forget. doin it manually is no fun. now to get the spark plugs an wires changed while im waitin on parts.

Plugs were something else 75 to 80 gaps on the three fire wall plugs think they maybe oem with 175 thou on the really tough to pull and the three in front were split posts heavy wear on these also. Put iridium'* in won't be worrying about them for a long time.
Replaced the HVAC controller an the auto works an keeps temp steady, couldn't get center vents to work, so will have to check into that an see whats out under there'
Have a fuel pump an sender to put in an will see if fuel gauge will work ,or if I have to put a stepper gauge in the dash an change burnt out lights will check the vents out with the dash apart an with parts in hand fix what I can lol

Okay a couple months have gone by, found the right/passenger side a/c damper door actuator was stripped inside so the motor ran and couldn't get a hold to turn when weather is cold works some when it'* warm out, kind of, more like i didn't notice cause my feet weren't cold putting it back together now.
FYI Actuators, it says not to run these without them being installed first.
Fuel gauges work again, but I can still spin the needle behind peg by turning the key straight to start with out a pause. I found if I let IP lite up, pause, then crank it it'* fine and works as it is suppose too.
back to work for me.

It is correct that the 98 PA has electronic controlled doors for both the drivers side and the passengers side. This gives the control feature the passengers ability to run the passengers side a few degrees warmer or cooler than the drivers side. The actuators that control both temperature doors have a circuit in each that is checked by the HVAC Control main unit each time the system is activated. The actuator moves through it'* range from hot to cold and relays that information back to the main unit. If the doors become stuck there is a good chance that the actuator will move through the test range and will strip the gears in the actuator. Each actuator has a small DC motor that has enough power to break the gears if the door is stuck. New actuators cost somewhere in the range of $100. It is recommended if a new actuator is installed that the dealership calibrate the actuator with a HVAC piece of equipment. I didn't do this and my second actuator broke the gear after I installed it. I gave up. I am currently using a small pair of vice grips on the control door lever and can set the temperature either towards hot or cold like a manual controlled unit. The actuator on the passengers side works great for both hot and cold so I have some ability to control the temperature overall.
I know this sounds a little complicated but I have spent many hours researching, reading shop manuals and trying to get my heat and air working correctly. My decision is to live with it because of the cost of repair through a dealership.