Bret 944

I just converted to 134a on the Turbo. I filled the system with freon until my gauges (checked with 2 different gauges) were at the upper limit of the OK range. The air coming out is not as cold as it should be (haven't used a thermometer, but I'm guessing it's somewhere in the range of 60-65*F. Shouldn't it be much colder? When I did the conversion on the '88 I was getting temps in the low 50's , maybe even in the 40's (used a gauge for that). What gives ?

Porsche-O-Phile

Did you eliminate completely the old freon & oil from the system?

SamGrant951

Ice Cold?

Bret 944

Nice Sam...yup, old stuff has been evacced (is that a real word ?)

Campeck

you stole my line

SamGrant951

Alright alright alright alright alright - now ladies....

Campeck

i want to see you on your BAddddest behavior.


ok...im done.
wouldnt it be evacuated?

is it possible for the exchanger to get clogged? probably not your problem but im just wondering.

Porsche-O-Phile

A couple of possibilities -

(1) bad expansion valve
(2) partially blocked expansion valve (due to ice maybe?) This can happen if there's any opening of the system to the air prior to introducing the refrigerant after it's vaccummed out.
(3) stuck heater valve (???)

Zero10

Start with the simple stuff. You charged it to the upper limit of the OK range. It might be a bit overcharged. Overcharging causes a significant decrease in cooling ability.
Next, with all of the 944's that I've done A/C work on (3), I have found that at idle, the air will blow somewhat warm (unless charged with R12, then it's ice cold all the time), but once you're at 2000RPM, and moving, it blows a LOT colder.

If it's still warm at speed, I'd start by checking the high and low side pressures again, see what's going on there.

Bret 944

No, it's cool, I just don't think it's cold enough. Maybe it's just the difference between the old stuff and the new stuff. I know the R12 should be much colder. Maybe I need to replace that one part (I think it's the drier ?) that some people have suggested to replace when doing the conversion. Maybe it's what Jeff suggested.

I'm happy that I have some cool air at least. Good for one, but certainly not cold enough to cool 2 people.

Zero10

If it's not COLD when moving, then you have a problem.

If the R134A and the new oil was put in without evacuating all of the old oil (i.e. draining the line to the condensor, draining the compressor, and changing the receiver/dryer), it's possible that the oils have reacted negatively, and have partially clogged the expansion valve. I've seen that happen before. I put R134A in my 951, and (before it all leaked out) once I was up to about 20-30kph, it was cold enough to make my hands very cold, and make my whole face cold, it was about 25*C that day. If I had to guess, I would say I had a vent temperature of around 3-4*C. When I was idling in traffic however, it came up to more like 12-15*C, which just wasn't good enough.

Once you have the compressor speed up, and adequate air flow over the condensor, R134A should actually blow colder than R12.

Remember, it's the evaporation of the liquid refrigerant that makes the evaporator cold. If the pressure in the system is too high, the refrigerant can't evaporate fast enough to keep the evaporator cold. This is why overcharging is bad. You said you charged to the upper end of the OK range. What was the ambient temp, and what was the low side pressure?

How often does the compressor cycle?

Tony K

What has your experience been with compressor cycle times?

When I drive on the freeway, I sometimes listen to the clicking of the relay (loud click off, faint click on) for the compressor cycling, and time it. (yes, I'm an anorak)

Going from memory (may not be all correct):
At 3000 RPM, I get a range from about 8 second on/14 seconds off on cooler days to 20-25 seconds on/8-10 seconds off when it is 95F outside and sun directly overhead. On a typical 80F degree sunny day, at a sustained 3000 rpm in 5th gear, my compressor will cycle onff at a 2:1 ratio or slightly less, with on ranging from 14-20 seconds and off from 8-12. To get a 1:1 ratio of compressor cycling, it has to be more like 70F outside. To get longer off times than on times, it pretty much has to be 60F or below, i.e. cool enough outside to just roll the window down and not use AC.

Do these numbers sound about right to you? This is with R134a and an otherwise stock AC system on an 85.5 NA 944.

Cheers,

Tony

Bret 944

Ambient temp was around 80F or so, maybe 85F. I figured this would make my readings a little higher than normal, so I just put it at the very upper limit of the "Ok" range on the gauge, thinking that would leave me somewhere in the middle of the range if the outside temp was a little cooler. I'll have to check the compressor cycle. I'll try and listen for that this afternoon. Normally I have my radio too loud to hear it.

Bret 944

Also, where is the expansion valve located on the car ? I see there only about $35 at Paragon, I'll replace it if it's not too difficult to get to, it's not worth all that much trouble to me.

951Tom

Easy way to the expansion valve on a late model car is to remove the blower housing at the base of the windshield. Then you can reach right in with wrenches. The valve will be wrapped in black gooey insulation.