A tale of two A/C conversions
 

DIY R134 conversion.

1. 1988 W124 300E, new compressor, receiver drier, expansion valve, all O rings. Converted to R134. Fully charged, no leaks. Low side, 55psi @ 90F ambient. Vent temps only 66F :(

2. 1987 Peugeot 505, converted to R134 last year, Ambient 90F, vent temps 46F :)

How can I improve the Benz's temps without going to R12?

What happens to the W124 vent temps if you spray water on the condenser?

-J

Never thought of that but will try. Aux fan works fine, both speeds.

55 psi low side sounds too high, assuming your evaporator and fans are working. I would vent some off until you get 40 psi. However, R-134A should be recovered since it is a potent green-house gas (soon to be out-lawed). It also smells like ---- (how would I know?), though I heard it is used in Dust-Off cans. If you still can't get it to work, try Duracool or Enviro-Safe, hydrocarbons that work much better and have no environmental issues, but are flammable (so is R-134A).

Were the condenser & evaporator & hoses thoroughly flushed? The MB AC conversion tech sheet says to remove r12, pull vacuum, add captured r12 back in, and remove it a second time to extract the mineral oil in the system, but that is just not enough. The evap, condenser, and hoses should have been flushed separately a few times to get the crud and oil residue out.

Next, did you remove the wiper mechanism and blower motor to clean the inside of the heater box? Dirt has been building up on the fins of the evaporator for 25 years. Spray AC cleaner foam in and flush slowly with water. It drains out the two drain hoses.

Hopefully, you will return to "the best of times" from this "worst of times"!

55psi is too high. I have a r134a conversion. I run 26oz of R134a which net me 55psi low 280psi high at idle with 113F ambient and blow 40-50f freeway and 50-60f idle depending on time of day same ambient.
Whats high side pressures and how much oil did you put in?

@ 40psi or 55psi, ambient 90F, I get the same vent temps in the 60s. I don't have a high-side gauge but I do have a vacuum and the system was cleaned, thoroughly and purged. Oil amount added to new compressor is to spec. I need to ditch R134 and try something else because the a/c system I believe is fine.

This chart shows you where you should be on pressures.

http://www.ackits.com/aacf/ptchart.cfm

You did a lot of work here; you should pop for a gauge set and do a thorough analysis before throwing in the towel. It's true that 134 won't do quite as good a job as 12 in a converted system, but it should cool acceptably well if set up properly.

DG

DG

That's the mystery. I did nothing to the 87 Peugeot other than change the fittings and it blows nice and cold. 300E was converted by a shop ~5 yrs ago and was just marginal, never super cold. Last year I replaced the compressor and went through the whole system and still my vent temps aren't cold enough.

Update: 80F outside ambient today. Vent temps 70F, Low pressure 45. I tried spraying the condenser with cold water, no change. My plan is to evacuate the R134 and try Enviro-Safe. Any caveats?

Your low side pressure
http://media.heavy.com/media/2013/05/damn.jpg

Or just get a different refrigerant. Propane works well.

+1. at 80 ambient, your low side should be around 35.
It's said that if your little low that is ok but should never be high for proper functioning a/c.

You need to see what your high side pressure is before continuing. Go grab yourself a gauge set.

I wonder if your heater core is getting some hot water through a leaky shut off valve. 134a is not the problem. I have converted two R-12 systems to 134a, and had trouble with one system freezing ice in the evaporator, so 134a can put out cold air.