85 Buick Park Ave heater/AC problems

[toolive65]

My 85 Park Ave seems to blow hot air whenever Im driving. It blows from the bottow of the dash and from the vents if I turn the AC on which dont seem to work either. Its 95 degrees here in GA and its driving me crazy. Can anyone give me a clue as to where to start. Hot airs just blows hotter and hotter the more I drive. Especially on the interstate. The heater will blow if I trun it on but it does not have to be on to feel hot air comeing from from it. What could be the problem? Thanks.

[T-Type]

Sounds like a 'flap' in your ductwork is not moving to the correct position for AC or vent. In other words it sounds like it is stuck in the heat position. All the air coming into the car is going through the heater core. I believe the controls for the flap are vacuum operated for GM cars of that era. With the car idling, blower off and radio off, slowly slide the switch between heat and AC and back. You should be able to hear the flap move as you move the switch. If you hear that, the flap is probably working OK and it's something else. If all you hear is a constant hiss you have a vacuum leak in the dash and that is why the flap is not moving. If you hear nothing, your leak may be in the engine compartment.

BTW when you turn the AC on, does the compressor stay on or or does it cycle on and off? Do some of the AC lines in the engine compartment get cold when the AC is on for a while?

[toolive65]

Thanks for the post T-Type, I tried switching from heater to AC and I heard the flap close. Air bllew thew the AC ducts and when select heater, it blew out the bottom duct. But I noticed that even when blowing out the AC duct, it continued to blow out the heater ducts too.
And as for the AC, the compressor runs continuously even when I seletect heater and all of the lines leading to the compressor get hot.

[rmodys]

Sounds like the heater door is stuck open. If it's anything like a G-body, the A/C, heat, defrost, etc. will be vacuum operated and the air mixture will be operated by a metal wire type of deal. This can get unhooked or stuck, causing the car to blow hot air at all times.

[toolive65]

Thanks alot, I will check that ASAP and repost as soon as I find out.

[73ChevelleSS]

Does your car have a digital control head,or a manual control system?The auto ac system that uses that digital control heads had a lot problem back in the day.I use to have a 1985 Park Ave with the auto system and a digital head.After 1985 Buick stoped using them if I remember correctly.

[Triple-X08]

if its automatic then it could be a actuator problem, or control head like mentioned. if its vacuum then more than likely a line has deteriorated over time or you may have a bad valve in one of the vacuum actuators, does it only have 1 mode or can you still move it from floor to defrost to bi level to chest etc. if it can do all those then you may have a stuck blend door or a bad vacuum line going to it. you could take a vacuum pump to the actuators and see if they move, if they dont then you know its either a actuator or a stuck door. remove the actuator and see if the door moves freely.

if its cable operated, then it could be bound up, or possible a bad cable. lots of possibilities.

its alot of work, but it will help you diagnose your problem strategically.

when you have problems like this it could be something simple like a vacuum line, or something major like a bad door.

reminds me of a similar situation with the astro vans, they have a vacuum controlled hvac system, and sometimes they burn a hole in the vacuum supply for the hvac system. there is a line located on top of the intake manifold that likes to burn up, thus supplying no vacuum to the hvac system, and in the process the hvac goes to the defrost position. and stays there. so im assuming this is something like what your having, except with the temperature settings. so im assuming its a vacuum problem of some sort.

[toolive65]

The control head is digital and air does switch between the heater/ ac/ and bi level/ defrost. I will check the actuator to see if its functioning properly. This is great info guys, Thanks.

[73ChevelleSS]

Originally Posted by toolive65

The control head is digital and air does switch between the heater/ ac/ and bi level/ defrost. I will check the actuator to see if its functioning properly. This is great info guys, Thanks.

The control head is junk.

[GMFreak8]

Did you ever get this taken care of? I have the same issue in my Buick Park Ave, although it's a 1990.

I accessed the controls behind the glove box and there is a metal rod sitting on top of a black box right behind the glove box. This has come undone. If I move the rod back and forth I can control the temperature of the air, but if I leave it alone nothing is controlled automatically. Can anyone tell me how to go about fixing this? The heater is constantly stuck on, even with the fan off. I have the digital control head and I can set it to 60 and it still blows hot air at the highest fan speed. I also can't select any of the vents, it's stuck on floor mode. When I select any other mode very little air is deflected away from the floor and to the body level vents or the defrost. I can hear a flap move somewhere but only the slight amount of air is redirected. It's becoming an issue now that it's getting colder. Defrost is a must around this area. if anyone can help me get my vent selector working along with being able to actually control the temperature of the air coming out I would greatly appreciate it.