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Improving 1976 Buick Electra A/C performance

cmeseadoin on Wed September 10, 2008 8:26 AM User is offline

Year: 1976
Make: Buick
Model: Electra 225 Limited
Engine Size: 7.5L
Refrigerant Type: R134a

Hey guys,

I just recently purchased an A6 compressor for this car on ACKITS as my original one I was using was leaking at the compressor shaft seal. I have flushed the system, added the correct amount of oil and installed the new compressor. Everything is doing really well and the compressor is not leaking with no other leaks in the system either. I have the system recharged to where I was seeing optimal performance, however, I would like to see if anyone has an ideas on how I can improve performance a little more.

My problem that I have always had with this car is that IDLE performance is lacking. When I first put everything back together, I was only getting about 57-58 degree air from the system at idle on next to highest blower speed. It would cool down while driving. I took the system down, made a CCW adjustment to the POA, increased my idle rpm at the carb a few 100 rpm and put it back together.....long story short, right now, I am getting about 48 degree air from the vents on the third highest blower speed out of four at idle on an 88-90 degree day. When driving, I am able to get the air temps on the same blower speed down around 40-41. On the next LOWEST fan speed, I am able to achieve about 37 degree air. This is a def. improvement in performance. I am wondering whether I should take the EEVIR apart one more time and make another adjustment to the POA. So far, I have turned the screw about 1 full turn CCW from where it was when it was giving me 58 degree air. I am def. happy with the results, but would like to get my air temps into the low low 40's or better yet, high 30's at least while in idle. This car has a LOT of glass surface area and it is important that the vent temps be cold to take up for the solar radiation from the glass surface. Right now, while driving, she really ices down....but still see a warming trend into the upper 40's when idling.

Any ideas? Fan clutch is bran new and working as designed. I cannot recall 100% what my pressures where offhand....but I screwed around with adding a little refrigerant and monitoring pressures and also letting some refrigerant out and monitoring evap low pressure.....and found right now, this happy medium. I'm getting closer, just looking for ways to get that evap as cold as possible with the least amount of compressor rpm / hence idle. Thanks!

mk378 on Wed September 10, 2008 10:01 AM User is offline

If the low side is above the POA setpoint, adjusting the valve will not affect system performance. It is already wide open regardless.

cmeseadoin on Wed September 10, 2008 11:53 AM User is offline

Ok, I am not an a/c expert....can you explain what that means? I understand the point you are making, but how would I measure or check this? I do not know how to tell the correlation of where the screw on the POA is set at vs. what the low side would be. I am assuming that as I make CCW adjustments to the POA(opening it up), that the LOW side pressure would be dropping X amount each time, thus allowing the evap temp to be lower? What you are saying is there is a point where that POA is wide open and you're not going to get a better low side pressure or evap temp?

That makes sence to me, but I am not so sure mine is wide open yet with where I have it set...so how do I look at low side pressure and determine where my POA might be with regards to a spectrum from 0-100% of "open or closed?" Is there a metric I can use such as running the a/c at idle with the blower unplugged allowing the low side to hit it's lowest/coldest pressure...and seeing where that is and then determining whether there should be a way to get it a little lower? Or is the easiest thing to pull it down one more time, open the POA more and hope for better results....worst case it would be wide open and the best cooling I will get with all other variables in the system where they are?

cmeseadoin on Wed September 10, 2008 11:58 AM User is offline

Quote
Originally posted by: mk378
If the low side is above the POA setpoint, adjusting the valve will not affect system performance. It is already wide open regardless.

I just re-read this and I do see exactly what you mean from a settings vs. real performance standpoint. I'm just trying to understand if there is a way to use various variables to determine how close to or if I am at that wide open setting....It would not be such an issue if I could easily make an external adjustment to the POA, but I have to discharge the system each time and open up the EEVIR and take out the POA. This is why I am trying to use some science to estimate adjustability.

mk378 on Wed September 10, 2008 3:22 PM User is offline

The adjustment screw does not directly open and close the valve. It sets the pressure where the valve will open and close.

At idle, with the interior blower on high, typically the compressor cannot pump as much as the system would like. The evaporator pressure will be above the setpoint and the valve will stay wide open. Vent temperature necessarily increases, but this is not due to the valve but from other issues.

Once the pressure starts to come down, the valve partly closes and restricts flow out of the evaporator. This reduces the BTU capacity of the system, keeping the evaporator from getting too cold and freezing up.

fonebone on Mon September 15, 2008 1:15 AM User is offline

I have followed closely here all the work involved to adjust a pre-VIR, in line POA valve over the years. Correct me if I'm mistaken, but this is the first case of someone adjusting a VIR POA valve. Is this possible? I've not seen another post that said this could be done. To the pros out there, what say you???

Edited: Mon September 15, 2008 at 1:15 AM by fonebone

2005Equinox on Thu September 18, 2008 1:22 AM User is offline

Does a 1976 even use a POA. I thought in 1975 GM changed to the cycling systems.

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