OT: 2000 Pontiac Bonneville: HVAC blows warm when cool is selected

[GM Guy]

hey all,

working on the sister's 2000 Pontiac Bonneville with the 3800 V-6.

The issue is with the HVAC. It has the manual system with two knobs and 8 buttons, rahter than the little digital display. It blows warm when selected to cool. with 250K miles, the knobs are well used, and the temp selector is sloppy. you can turn it to cool, and go one "notch" at a time, and get a fairly large temp change, so I am wondering if the control module (the whole mini-dash unit, with 2 knobs and buttons) is wore out and needs changed, or are these cars famous for bad blend door actuators?

no matter what, I hear this car has CANBUS, so I am worried that I may need to have a tech II involved to change any parts electronic, as in get the CANBUS system to "recognize" the new parts. is this true, or can I change whatever with the battery unhooked, then hook it up and be fine?

finally, is there any way a tech II can aid in the diagnosis? I may take it to our local dealer if this CANBUS system is too much for me.


on a side note, we just put a can of freon in, and now it blows cool (had 15 lbs in the system, so just added freon. dad insisted on adding an ounce or so of ester oil against my recommendations) but not cold, so we are still combating the issue of heat intrusion into the system.

any input appreciated, thanks!

 

[WarWagon]

System is low on freon and starving the compressor for oil in it's current state. This is the reason it isn't "cold" or "cool". May have other issues, but, for sure low on R134a.

Look for any leaks. System was nearly empty having just gas in it - no liquid.
Add two more 12 oz cans of freon to get slightly over what the system calls for. 36 oz. You could find cans with odd capacities like 16 oz to add up to 2lb.

Google will quickly give you what you need to know about the AC specs. Some GM stuff has gone to PAG 46 per a TSB.
2000 Pontiac Bonneville freon capacity
32.00oz 134a freon oil PAG 150 9.00oz

If you dad has a gas engine tell him to toss a quart of oil in the gas tank and watch it smoke. It has about the same effect as randomly adding the wrong oil to AC systems. Unless a part is replaced or there is an oil stain around a leak the system does not loose oil. So the system generally doesn't need oil and especially doesn't need the wrong oil.

 

[GM Guy]

will put some more in, but would like to solve the root problem, the screwy controls.

on the freon charge, one can was enough to get the safety switches to release and allow the compressor to kick in. we only used the low side port to keep from having fun with the high side like we did with the 98 K2500. running at idle, what PSI should we have on the low side to see if we have enough?

 

[WarWagon]

Charge by weight. Pressures vary by temperature and are WORTHLESS to charge the system.

 

[THEFERMANATOR]

System is low on freon and starving the compressor for oil in it's current state. This is the reason it isn't "cold" or "cool". May have other issues, but, for sure low on R134a.

Look for any leaks. System was nearly empty having just gas in it - no liquid.
Add two more 12 oz cans of freon to get slightly over what the system calls for. 36 oz. You could find cans with odd capacities like 16 oz to add up to 2lb.

Google will quickly give you what you need to know about the AC specs. Some GM stuff has gone to PAG 46 per a TSB.
2000 Pontiac Bonneville freon capacity
32.00oz 134a freon oil PAG 150 9.00oz

If you dad has a gas engine tell him to toss a quart of oil in the gas tank and watch it smoke. It has about the same effect as randomly adding the wrong oil to AC systems. Unless a part is replaced or there is an oil stain around a leak the system does not loose oil. So the system generally doesn't need oil and especially doesn't need the wrong oil.

If there is enough charge in the system for it to run, then the compressor is not starved for oil. PAG oil mixes with liquid AND gas forms of R-134A, NOT just the liquid form. And do not under any circumstances overcharge an A/C system by more than a 1/2 lb with an accumulator equipped system, if you do liquid charge can hit the compressor and destroy it. Feel the low side line at the compressor and see if it is cool, if not then get gauges on it and see what your head pressures are. And take your dad's ester oil and throw it in the trash can. Go down and buy some of GM's universal PAG compressor oil to put in the GM systems. It is roughly a PAG 120 viscosity, but is designed to have better shear stability than the PAG 150 they used to use. And yes the blend air door actuators are electric and can fail just like any of the others. Also grounds are ciritical to them since they work via a low voltage trigger to vary there operation. And in 2000 it is not a canbus system as GM didn't go to that for vehicle coms until 06.

 

[GM Guy]

So would it a wise idea, or a waste to change the control panel, or do you think its in the actuators? I think we will try the controller, whats 250 bucks? Sister got a promotion, and she lives here on the farm, and is about as cheap as my old man, so needless to say she can spend a little.

we will keep that ester oil for other systems (I am thinking due to the supposed R12 and R134A compatability, it would be great in an old tractor that came with R12, and is getting converted to R134A.) but I will try to ban him from using it in the vehicles.

So the PAG 120 GM universal is your preferred oil to keep in stock if a guy was to only use 1 oil? or should I still get some PAG 150 for the R4 equipped rigs?

thanks for all the input guys, it is much appreciated.

 

[WarWagon]

With the freon the additional $250 control panel totals that car depending on how much gas is in the tank! :rof: Time for her to get a real vehicle and drive a 6.5 equipped diesel pickup. :thumbsup:

If you added more freon as outlined above...
Check the accumulator for being cold. The inlet and outlet of the evaporator should be about the same cold temperature.

Next get a bypass valve for the heater hose. It is cheaper than a new control panel. Little manual change under the hood for heat...

You can listen to the doors move with the blower on low engine off. Move the heat/cold selector and listen to how much the doors move. Should be the same for each step. If you get a door that moves on it's own or is hunting then you have a bad actuator. They don't last forever. Check grounds for the system first of course. Amount of temp door movement can be either the actuator or the control panel if it is excessive. Usually actuators will hunt when bad. They should move to a spot and stop. Some will change position with airflow pressure on the door from a bad actuator. Esp bad rec doors on 1995's swapping modes with speed/airflow. (How and why I don't understand well.) You can literally push it with your finger and have the actuator move to the full other end of it's travel on it's own. You can run the blower speed up and see if the blend door moves.

I have had them intermittently hunt on me. The blend door on my 2005 would do that.

Junkyard may have a good control panel.

 

[GM Guy]

I will listen closer, but have never heard any hunting or flopping, like the bad actuator on my 91 gasser. since it is dead quiet, I think we will try the actuator. the backlights are out on half of it, so might as well get a good one with all the backlights!

Sister can afford to put a little in this one, it is rust free and in excellent shape for the miles, just some local businessman's traveling car. he owns a few radio stations across the state, so he drove quite a bit.

the heater idea may not be too bad, no quick connect, just two nipples, so a guy could loop a short piece of hose between the two, but one wouldnt dump any coolant if he talked his sister into spending 250.