Little Mouse

On a 134a system how much oil to refrigement should be run and
what is the limit for head pressure.

SIXFOOTER

I was looking at mine today, it said 3.75 lbs, thats 60 oz of R12. There was a thread in here the other day said 20% less for R134, so thats 48oz. I have an 81

Little Mouse

Thanks six shooter, I'm going to change the drier on my old wore out dodge raider I have a set of gauges and a 30lb tank that I use
on trucks. I'm trying to guess how much oil to put back in it after
I open it up and let all the fliud out. I think it will be ok with 325
of head pressure but not sure what the limit is for 134a

noonie

A good rule of thumb is 2 oz oil for each major componant.
Systems hold anyware from 5 to 10 oz total, so don't overfill. You can look up the specs for your vehicle.

325 is above the high pressure cutoff switch cut in limit.
Depending on ambient temps, on a good system you shouldn't run over 250 psi. Overfill is bad on compressors and other components. Try increasing condensor air flow to reduce head pressures.
I try to run anyware from 200 to 240psi @ 95* ambient.

With 134a, there is less leeway than 12, so fill the system slowly until the acummulator feels cold, you will be within 1-2 oz.

Little Mouse

noonie the book on this little 4X4 box shows 25-30 ounces of
refrigerent so its a pretty small system, I flushed the R-12 out
about five yrs ago and converted it to 134a. It lasted five yrs
before it got a lttle low on fliud I refilled it but it is not blowing
as cool as I want so I'm just going to pretend I blew a line and
let the fluid out into the atmosphere ( sorry environmental
***** ) and replace the drier and whatever it uses for an
expansion valve. Last time I used a 10.5 can of oil but I think
I went a little overboard on the oil for such a small system. I
think ill use two of the small 4 ounce cans of oil. I was told yrs
ago for R-12 systems the limit for head pressure was 250 and
made sure it never went over 225 out in this hot miserable Texas
hole I have lived in for the last 35 yrs . I thought these 134a
systems ran higher head pressure and have been running 325
maybe I have just been lucky.

zwede

Unless you're flushing the system you are not removing much oil. You probably won't have to add any at all.

noonie

Sounds like you have too much oil.
Too much oil=less freon=less cooling.

In a lot of r12 conversions you have to add a pressure cutoff switch, so that's probably why it ran at a high pressure for 5 years. Your compressor may be worn now. You may also have a leak. You should never loose freon.

You never mentioned using a vacumn punp, but you must use one to refill. Refill without adding more oil until the dryer gets cold. A lot of people overfil with 134a.

try misting water over the condenser and take the pressure readings. If that gets you in line and you get decent temps add a pusher fan. The oringinal condenser is not optimal for 134a. You really need a parallel flow condesnser, but a fan can fake it.

I'm in S Florida, so the temps are about the same.

1Z87L8

Little Mouse

Zwede, noonie, Think your right probably been to paranoid about
burning up the compressor and have to much oil in it from changing
it over to 134a five yrs ago, letting out the freon almost all the oil
should stay in it, I was not thinking right It did do a pretty good
job cooling with to much oil in all this time. I may just reflush the
thing and start over with some new parts and closer to the right amount of oil. The book on this thing only says 25 to 30 ounces of
freon for the system, seems like eight ounces of oil may be enough
if I flush it and start over, would still like to have a little to much oil then not enough, what do you think about eight ounces of oil ???

zwede

Off the top of my head 8oz sounds low. Your service manual should list the amount of oil and you use the same amount as stock.

Keep in mind that most of the oil is in the compressor so if you are starting over with a flush you also need to drain the oil from the compressor. There should be a drain plug on it somewhere.

mdj21

8 oz is correct for an R4 compressor. the A6 is more like 11oz.