Yet Another...AC thread. Checking..
 

Following the book...10minutes at 2000rpm, setting 2 on the fan.

http://www.speedtoys.com/idlehold.jpg

Check

Amb temp, 35c on the nose.
R134 data:

Expected low pressures, 9.5-12.2psi
Expected high pressures, middle of the road is 253psi.

What I have:
http://www.speedtoys.com/acpressires.jpg


Vent temp..barely 70d.

For the LIFE of me I cant find my infrared temp gun, feels about the same top to bottom of the condenser...but damn..where is that IR gun...

Front exp valve is new, its "cool"..but not cold.

Im not far mentally from getting some cleaner for the condenser..and another new dryer..

Thoughts?

Gonna go let it settle, and see where the amibient air temps settle in the system.

When I started the car, they read 30c, 5c under ambient.

At 90f, 2000rpm

Condenser inlet 175d
Condenser outlet, 135d

The temps at the expansion valve were like 117 inlet, 102 outlet...huh..

Sight glas very foamy. Why do I think that the Porsche 134 pressure numbers are too low?

If the sight glass is foaming you don't have enough refrigerant. With the pressures you are seeing I would say you also have some moisture and significant air still in the system. The air in the system is causing the high side pressure to appear normal. If you add refrigerant you will see the high side pressure increase as the air is a non-condensible gas in a refrigerant system. Did you do a proper evacuation and dry out after opening the system? If you have leaks you will never get the air out. If significant air and moisture have been in the system any length of time it will take several deep vacuum session with refrigerant flush between each to draw the moisture out of the system.

Mike

Sorry if I missed it but you vacuumed out the system and replaced the drier? Going through all of this now too. Also are the dampers working?

Just to get back on track..

I pulled a new vacuum today.
Refilled it with pure 134a, no addatives/etc.
Filled it to Porsche numbers, which at 28c are..

Bout 10-11psi low
Bout 145psi high

Did that at 2000rpm with fan at 2.

Hot inlet to condenser 195d
Cool outlet from condenser 135-140d, pretty good drop in temps across the condenser??

Expansion valve was of course, hot on the inlet, and chilly on the gas side...but my temp gun from NAPA..im positive its not really reading the tubes right there very well..but if feels cold on the outlet.

Vent outlet temp...60d.


Tomorrow gonna re-check the hot air valve..which -was- new at the intake refresh.

I also found a rare can of Kool-It evaporator cleaning foam..will do that tomorrow as well. (Its rare in Norcal, but NAPA had 2 cans on shelf)

Do you still have foam in the sight glass? If so, you still don't have enough refrigerant. You need to weigh in the charge, which for R134a should be approx. 1050 grams or 37oz. if you have rear air. Three 12oz cans of R134a will get you close.

June of '88 R12 charge is 1200 grams with rear air. In July of '88 they dropped charge to 1150 grams of R12. When converting from R12 to R134a you need to use 90% of the R12 charge as the charge weight for R134a. So 1200 grams * 0.9 = 1080 grams = 38.1oz and 1150 grams * 0.9 = 1035 grams = 36.5oz.

The charts you are using will not tell you if you have the correct amount of refrigerant in the system. They will tell you that all parts of the system are functioning at their design condition and the refrigerant is not contaminated with air or moisture.

Mike

I have dual air, but the rear is plugged at the return, so no flow there.

Im working off manifold pressures, and there is some foam in sight glass, which isnt, AFAIK, useful at all for R134 systems. But Im willing to learn more, but that is what ive read in a ton of places.

Really appreciate the level-set there Mike.

Best to pull a vacuum using a micron vacuum gage.. You'd want to get the vacuum down to 700 micron before adding refrigerant...

that's the only way to ensure you have all the moisture removed and don't have small leaks..

http://www.omega.com/Pressure/images/DVG-64_m.jpg

http://www.omega.com/Pressure/images/DVG-60_l.jpg

http://www.omega.com/pptst/DVG-64.html

http://www.omega.com/ppt/pptsc.asp?ref=DVG-60

Otherwise, your just guessing.

Seems to me your system is undercharged... how much refrigerant did you put in? Are you charging by pressures instead of by weight? Forget the sight glass with R134a, it will not show you anything conclusive. If you were charging by pressures, 145 psi high side at ~80 deg F ambient and 2000 RPM means there is not enough refrigerant in there.

Dan
'91 928GT S/C :eek: 475hp/460lb.ft

Even with the return for the rear system blocked you should still need close to 36oz for a full charge. If the rear system was functional the bulk of the refrigerant mass for that system would be in the liquid line up to the solenoid valve when off or the expansion valve when on. I'm assuming you still have the liquid line and solenoid valve in place so the need for the larger charge weight is still present.

As far as foam goes, even with a full charge you will see occasional bubbles. If you still see steady foam you don't have enough refrigerant. A lot of people mistake the cloudy look of the sight glass in a R134a system as foam. The mineral oil in an R12 system is very clear. The PAG or POE oils in R134a systems tend to be a little milky. You will never get the sight glass crystal clear with R134a. However, you should not see any obvious bubbles.

It is best to check your vacuum with a micron gauge, but you can do a good job of drying the system by drawing a deep vacuum for 3-4 hours, then break the vacuum by dumping a full 12 oz can of R134a into the system (not running) as LIQUID. Be sure you purge the air from the can tap and hoses before you add the liquid refrigerant to the system or you are just putting air and moisture back in the system. Repeat the deep vacuum and liquid flush twice more. Finally, pull another deep vacuum, close everything but the gauges to the system off tight and let it sit overnight. If you are still in a deep vacuum the next morning the system should be dry and sealed and you should be ready to charge.

Mike

Yes, Id agree, but I was looking at the WSM chart for pressures/temps.

Tomorrow, I will shoot for sight glass in steps, watching temps, and find where it peaks and drops off again.

I know NOTHING about R134.....but a well running R12 system should have vent temps well UNDER 30+F under ambient.....Sharky would consistently pull 50F under ambient (yes below freezing)....Bill and I tested it several times at his house and it always did it.....it was like a meat locker....stupid cold....I miss it....

The manifold pressures are often not helpful. They can be WAY high with the car not moving. The fans are not adequate over a long period to cool the condenser. I've seen way over 300 high-side when doing a stationary, engine running fill, not overfilled. I've gone as far as to put some box fans in front of the car while doing a low-side charge with the engine running for a long time, but even then the pressures can soar.

Fill be weight, not pressures, if you have evacuated the system. If you are using R134 cans, this is pretty easy. Warm the cans as you charge to help fully evacuate them. If you are using a large canister, then you need a scale.

Ya..k..just a close guessin game to go by weight, thats all.

Will reconvene tomorrah