72 250 AC question
 

I had my 250 AC system switched to 134a last summer and it is just not keeping up. A mechanic friend suggested replacing the condenser with one that was originally fitted in a car with 134a - he said my condenser is undersized and is most of my problem. Any ideas as to where and what kind of condenser I should be looking for? Will any condenser work as long as it fits in my space? Has anyone done this before? Thanks.

Ryan

Your mechanic friend is correct. When you make the switch to 134a, you need 20 to 25% more condenser capacity than your R12 system. Most R12 condensers were tube-&-fin designs. There are new condenser designs used with new 134a systems - the serpentine condenser & the parallel flow condenser. These designs have greater capacity, and one or the other will give you the extra capacity you need at probably the same physical size as you original condenser.

Other things to consider:
Did you install a new compressor? Some older compressors just don't work that well with 134a, some work fine. Did the person doing the conversion have knowledge of this?
Were the expansion valve and evaporator pressure valve changed when your conversion was done? The originals don't have the proper calibration for 134a.

Solution: (IMHO) Find your best local A/C shop and have them suggest the proper condenser, and have them check the rest of your system components to make sure they are correct for use with 134a.

Good luck!

Not to say that a higher capacity condensor wouldn't help, but my 280C has been converted, and works great with the original.

Agree with the comment on the expansion valve.

What temperature are you getting out of the vents? Is the aux fan coming on at idle?

I went to possibly the best shop in OKC - they did not change the compressor (York) but they did change out the expansion valve and drier.

I am only getting about a 15-20 degree difference out of the vents, the coldest I have noticed lately has been about 65. The auxiliary fan only comes on at 212 degrees and I do not notice it coming on at idle, usually only after I turn the car off with the key on. While running, my temp gauge consistently stays just above 175 (new radiator this past spring), when I turn the car off the gauge will read higher temps. Does this make sense?

Thanks, Ryan

Yes, it's normal for the coolant temperature to 'spike' briefly after the engine is shut off. Retrofitting to R134 has been very controversial. Some claim good results while others experience problems. Did they thoroughly flush the system? Use the right type of flush agent? Get all the flush agent out? Add too much refrigerant oil? Compressor shot? Hard to diagnose the AC without the pressure guage readings, which will tend to read somewhat higher on an R134 system than an R12 system. One other thing to check on the W114/W115 cars is correct function of the air flap that diverts the dash airflow from the heater/fresh-air blower to the AC blower.

Happy Motoring, Mark

Pressure readings are 45 psi low side and 225 psi high side, dependent somewhat on ambient temperature. I have double-checked the control lever and it seems to be working fine.

Ryan

45 low side is way too high I believe. Mine is at 25-26, and mine's pretty cold. The system won't take as much r-134 as it did r-12 because it runs at higher pressures. You need a refrigerant chart to convert pressures between the two to se what the freezing points are at different pressures. I topped my r-134 system off with my mom's cousin who use to do a lot of refrigerant work on houses and helicopters.
Thanks
David