PorscheFanatic202

Finally got the AC system to hold a vacuum and filled it up using (r134a) 1 can first charge, 2 cans of refrigerant (12oz cans). It is sort of cold when im driving around (guessing it is maybe 75 deg air coming out of vents) when it is 95 outside and dry.

Gauges read at idle 30-35psi Low and 250-275psi high. Replaced the dryer, but i'm starting to wonder if I didn't flush the lines out well enough. While flushing the lines out, the line started ****ting all over the place (brown pellets were flowing out). I'm guessing its the desiccant that somehow got into the system from the PO (perhaps the dryer was installed backwards). Anyway, I flushed those lines till nothing came out, but i'm starting to wonder if they got into the evap and I didn't flush that out. Just doesn't seem like its as cold as it could be.

Also, I didn't change anything out except for the condenser and the dryer and pressure switches and orings.

Let me know what you guys think. Thanks for your help.

Ski

Not sure...how much R134 replaces R12? You can overcharge...but check the vents under the cowl to make sure they are closing when you hit the Recirc button. If they don't close you are still cooling outside air. My car did that and had to replace the little vacuum actuators and Cold Air after that. If they don't close, you can tie wrap them until you can get the little units replaced. Just something to check.

racerxrick

I charge mine with about 80% volume compared to R22 and it's VERY cold. If I recall 1lb. 7oz??

PorscheFanatic202

16oz in a lb. So I think I have about 30oz. I'll try taking some out. I do notice, however, when I Rev it up the low side goes way down to like 5psi and high side barely goes up. High pressure valve port is after the condenser and after the dryer so maybe something is clogged in there still causing a pressure drop. Before the high pressure fitting. I'm not completely sure, but a mass balance should indicate that the pressure should increase on the high side unless there is some sort of loss of pressure during condensation.

PorscheFanatic202

Where are the vacuum lines that do this? Could one manually open the fresh air valve?

Ski

On each side of the fan cover, just forward of the windshield. You have two fresh air vents on each side, you should see a grate covering the opening, then the actuator with a vac line to it. You can work the rod manually to see it closed, then try your recirc button and see if they close.

griffiths

Refrigerant flow.....
Compressor to condenser,
Condenser to Drier,
Drier to TEV...........

lee101315

Also, make sure your heater valve is closed. Even if it looks closed, take it out of the car, and hold it up to the light...sometimes hot antifreeze can get through the valve even when closed.

PorscheFanatic202

I don't know if this is part of the problem, but when I turn the dial from cold to hot it definitely gets luke warm, but not hot. However, when I turn the defog switch on, some valve opens up and it gets very very hot air blowing out at full speed. The recirculation switch works (meaning I can see something moving inside the vent). Should I open up the evaporator to see how cold the evaporator is actually getting before troubleshooting many various valves and vacuum fittings?

lee101315

If check a few things before going crazy.

Make sure zero hot coolant gets past the heater valve.

Make sure fresh air isn't bypassing the evaporator.

Was the conversion to R134a done properly? Meaning, was the old r12 oil evacuated? Drier replaced? Expansion valve/orifice updated for r134? As it is, r134a gas in an r12 system is a compromise for many reasons...a sloppy conversion would make it even more inefficient.

There was a long thread started by another member...maybe Ehall, on getting cold AC in a 951. Another lister was modifying r134a condensers to fit our 951s...a lot of good info will come up with a search.

Either way, don't expect to have 50deg air coming through the vents on a 95deg day...it won't happen without modification.

PorscheFanatic202

thanks. Some of my searches came up with people not having to do much modification and just pulling a vac and filling up with r134a. I'll do more searching. Any threads come to mind?

lee101315

https://rennlist.com/forums/944-turb...ce-thread.html

Lots of good info here....

Turbo17

My research didn't indicate this was required or commonly done. Are you sure about this step? Even the Official Porsche R12 to R134a conversion documents didn't refer to this.

griffiths

The 944/951 has an expansion valve, not an orifice tube.
When converting to R134a you don't have to change the expansion
valve because the difference in superheat is negligible.

lee101315

I was speaking in general. Ive done tons of conversions on euro cars and forgot that the 944 has a weird expansion valve. In many other 80's-early 90's cars, like Mercedes for example, you can put an R12 and an R134a expansion valve side by side, and notice a difference of 2-3mm of the restrictor.