87 Buick GN A/C

[chicagoslick]

Has anyone encountered issues switiching from R12 to 134A? I had a low charge for 12 and I converted to 134A over the weekend and while the ac does blow cold it is not what I was expecting as the old R12 ran very cold. Additionally, the pressure switch at the accumulator does not seem to cycle the compressor on consistently. When I switched over I pulled system into a vaccum, checked for leaks, and added gas at low pressure port. The system took ~40oz, and the temp at idle in the car at the vents dropped ~25 degrees on an 80 degree day. Low pressure gage read ~40psi. The low pressure line never frosted but sweated with compresser running. I may add some more 134A until i see start of frost on low pressure line. Max pressure on low side should not exceed 60psi and I am well below that.

Any thoughts?

I recall years ago that the condensors on R12 systems were on the small side for 134A conversions, but not sure if that applies in this case...I think this more resides around the low pressure switch, but could be wrong...

thanks in advance for all responses,

87 Buick GN Stock

 

[SloGN]

To make the best use of r134a in a buick its best to swap out the orifice tube to a red ford orifice tube, This allows for a better gas exchange. The pressures will vary due to outside temps and also the type of fans the car has.

I look for the pressures to be around 42-45 on the low side. The high side pressures will vary based on temps like I said before and also if there are any restrictions in the systes like a stopped up orifice tube due to a failing compressor. But they shouldn't exceed 250 psi

I think the rule of thumb is 2/3 the amount of r134a when retrofitting a r12 system

HTH

 

[chicagoslick]

To make the best use of r134a in a buick its best to swap out the orifice tube to a red ford orifice tube, This allows for a better gas exchange. The pressures will vary due to outside temps and also the type of fans the car has.

I look for the pressures to be around 42-45 on the low side. The high side pressures will vary based on temps like I said before and also if there are any restrictions in the systes like a stopped up orifice tube due to a failing compressor. But they shouldn't exceed 250 psi



I think the rule of thumb is 2/3 the amount of r134a when retrofitting a r12 system

HTH

 

[chicagoslick]

Good to know concerning charge amount. The ac plate read 3.25lbs which translates to 52oz and I am at ~40oz. I will have to look into getting a different orifice tube. I am still concerned about the low pressure switch, but maybe that is due to a low charge...Usually low charge causes compressor to cycle more often...Maybe I am wrong...I will put gauges back on and watch for cycling...

 

[Nick Micale]

Since 134a is only 80% as efficient as R-12 and the 80's vehicles do not have larger condensers and evaporators like newer cars to make up this difference, it will never get as cold as R-12.

If your AC compressor is original, it is also a sure thing that its performance and efficiency is lacking.

It appears you are in a "moderate" climate zone, so 134a should work ok for you if the system is up to par.

One thing I have found when using 134a is the system takes it very slow, and I usually need to top if off after a day or 2. I measure the amount of 134a going into the system by how cold the dryer will get!

 

[Raeban]

Here is a chart that puts a little science behind the center duct temps of R12 and R134a based on ambient. Adjusting the pressure cycling switch can help with the short cycling. Turning the screw counterclockwise and target 21psi is a good starting point.

 

[Chuck Leeper]

A new condenser will likely help. [Recent thread on this.]
R12 hoses, [& crimps] don't hold charge as well as the newer barrier hose and bead lock crimps.
[Bead lock is much easier to assemble, too.]

 

[chicagoslick]

After spending some time with the car I discovered the low pressure switch was not working and subsequently the compressor was not coming on as expected. I removed the connector and found that the contacts were bent. I straigtened them, cleaned, and applied electrical grease. The system is now operating. Definetly not as cold as R12, but better than no a/c at all...Thanks for all of the responses and information...