Passenger side AC blows at 60F, Driver's side at about 73F, AC set to 60F

My passenger side AC vents were blowing hot air when I had the temperature set to max cold (60F).

I figured it was probably a bad passenger side blend door actuator and replaced it with one from Pick-n-Pull.  

I thought I would be happy when the passenger sided started blowing cold (60 degrees F as measured with a K-type thermocouple), but then I measured the drivers side temperature and found that it was running at about 73 degrees F.

So, I figured that the Driver's side blend door actuator wasn't working, but when I looked at the slots in the actuator pinion, it showed that the blend door should have been completely closed and the HVAC air should have been bypassing the heater core entirely.

The other two Driver's side actuators pinion indexing indicate that floor flow should be off as well as the defrost door.

Since the Driver's and passenger side AC vents are both cooled by the same AC evaporator, I can't understand why the Driver's side AC is running about 13 degrees warmer than the passenger side, unless the Driver's side blend door is cracked/broken.

The AC system probably needs to be topped off with some R134a, but that wouldn't explain why the two sides of the system run at different temperatures.

The Passenger "Comfort Control" is set to the neutral position.

Does anyone have any idea of what could be the issue?

Pulling out the HVAC unit to inspect/repair looks to be a fairly arduous job.

Thanks in advance.

Edit: Oops, I see that Larry70GS informs that warmer Driver's side temperatures indicate an undercharged system.
https://rivperformance.editboard.com/t13007-blend-door-actutor

I'll top it off tomorrow and report back on results.

If the AC refrigerant charge is low, the driver/passenger sides *will* be different temperatures. It's a quirk of the airflow over the cooler and warmer parts of the evaporator under those conditions. So if you *know* your fridge charge is low, fix that first.

https://www.electronicshub.org/ac-pressure-chart/

Tks Larry

I looked at the Factory Service Manual (FSM) to see what my low and high side pressures should be with a full charge of refrigerant (R134a) and what the AC discharge temperatures should be.

I hooked up my AC gauges to the Riv and the pressures were low (no surprise).

Today's ambient temperature and relative humidity were 78 degrees F and 43% humidity.

I had a partial can of R134a (about 1/3rd of a can or 4 oz by weight).

The acceptable pressures at less than 40% humidity and 80 degrees F are:

Low side:  35-41 psi  
High side: 170-230 psi

AC output temperatures at these pressures are acceptable within the range of 45-54 deg F

The initial low side pressure was about 20 psi.  After the 4 oz introduction of R134a my pressures went to about 31/160 (low/high sides).

The AC output temperatures after refrigerant addition went to
Passenger side:  55 deg F  (two days ago it was 60F)
Drivers side: 60 deg F  (two days ago it was 73F).
.
So, both sides got colder and were converging upon a single temperature - they were within 5 degrees of each other when they were 13 degrees apart two days ago.

Conclusion:  The system is working as designed and I should crack open another can of R134a and add enough refrigerant to get to the specified low/high side pressure and to get the system blowing air at the specified acceptable values of 45/54 degrees F at 78 degrees F, ambient temperature.

Driving in the summer is much nicer when the AC works as it should.

Thanks Larry70GS and Albertj for your help.

PS: The FSM said that if the input line to the evaporator was noticeably cooler than the accumulator, by feel, that that is a good indication that the system is undercharged. On my Riv, the input line to the evaporator was icing up when I turned on the AC - I think that's probably a good seat-of-the-pants test to know when your Buick needs some more refrigerant in the system. I have taken note of it for the future.

Great info it's gonna be a cool comfortable summer after this

YW

I opened another 12 oz can of R134a to get the AC system up to the specified low/high side pressures of 135/170 psi, respectively at 80 deg f and 40% humidity, ambient temperature/humidity.

I didn't think the system needed more than a few ounces since the pressures went up significantly with a mere 4 oz (by weight).

Surprisingly, the system absorbed the full 12 oz and the low side pressure only increased to about 133 psi and the high side pressure went to about 175 psi.

The passenger/driver's side AC discharge temperature converged to 45/46 deg F, respectively, which is in the FSM specified acceptable discharge temperature at the given ambient conditions.

Since the system capacity is 2 lbs (32 oz) and I've put 16 oz of refrigerant into the system total, I think I'll call the status quo OK, and save my remaining R134a for cars that need it more than the Riv does right now.

The last R134a is bought was in Montana since Washington State has decided to limit its sales to businesses that do AC work, etc.

brutusk1 wrote:

I opened another 12 oz can of R134a to get the AC system up to the specified low/high side pressures of 135/170 psi, respectively at 80 deg f and 40% humidity, ambient temperature/humidity.

I didn't think the system needed more than a few ounces since the pressures went up significantly with a mere 4 oz (by weight).

Surprisingly, the system absorbed the full 12 oz and the low side pressure only increased to about 133 psi and the high side pressure went to about 175 psi.

The passenger/driver's side AC discharge temperature converged to 45/46 deg F, respectively, which is in the FSM specified acceptable discharge temperature at the given ambient conditions.

Since the system capacity is 2 lbs (32 oz) and I've put 16 oz of refrigerant into the system total, I think I'll call the status quo OK, and save my remaining R134a for cars that need it more than the Riv does right now.

The last R134a is bought was in Montana since Washington State has decided to limit its sales to businesses that do AC work, etc.

Your pressures sound fine. The actual pressures you should hit will vary depending on ambient temperature and relative humidity (humidity affects how much heat the condenser can get rid of per unit time and so affects how the refrigerant condenses and so affects pressures). Your ambients were at an edge of the ranges in the table, so your pressures with correct charge amounts - well, it's no surprise they are a bit off.