CuttyShark

I agree that recover/recharge to weight would be the best course,however; Just trying to make it thru this summer. I'm planing on a complete evac for next year.

Here is what the new pressures /temps are. 100degrees outside.

slowly added 12oz.
1500 rpm 2nd sp.fan , rear off

( High-low-center vent -floor)

250-18-40-65 } stopped adding at this point then I turned the

rear on 2nd sp. -everything went up.. and fluxuated (compressor never cut out)

255-280

22-30

Center went up to 52 settled to 44 (net increase of 4 from 40 without rear on}

Are all these increases normal or something else going on?

Does it look like I have enough Freon ( if one can tell by the info)

Side note, I can hear and watch the rear unit cycle - only goes between 40-43 degrees.

Thanks

CuttyShark

Forgot to say : Sight glass is running pretty clear w/no bubbles. Before I started it was cloudy.

dprantl

What was the ambient temp? If it was in the 90 deg F range, then those pressures sound pretty good.

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

CuttyShark

2nd line:Here is what the new pressures /temps are. 100degrees outside.
thanks

dr bob

Pressures sound about right for conditions. 12oz is a LOT of refrigerant to add to a system that's already cooling. Did you watch the sight glass as you were adding? I would expect it would have progressed from vapor with oil smears through an obvious white froth/foam, then gradually reducing bubbles until it gets close to clear and just a few bubbles streaming by. This is where you should stop with R-134a, with pressure just below the bubble point. That gives you liquid at the expansion valve for full capacity, and lowest suction pressure in the evaporator for coldest possible temperature.

On your pressure gauge, there's a convenient temperature scale indexed to the refrigerant you are using. ASSuming that there are no impurities like air in the system, the pressure on the low-side gauge tells you the temperature that the refrigerant is flashing (boiling) at in the evaporator. Outlet air temp will be some 10-20º higher than that at full fan speed with full 40º air temp differential across the evaporator. Lower inlet air temp will make lower outlet temp, until you get to lowest temp results at around 10º approach. Impurities will skew the results drastically, however, since they don't condense and therefore don't boil on expansion into the evaporator. They hog liquid space and vapor heat-exchanging space in the evaporator, plus the partial pressure of gasses raises the evaporation temp by up to 30 degrees. Even a small amount of residual air in the system will push vent temps up into the 50-60º range in an otherwise good-performing system.

CuttyShark

Yes, watched glass, it is fairly clear, and I'm not sure I'm seeing any bubbles, but will road test to see performance.
However; One question...

While at 1500rpm, #2 fan, Why would I see immediate temp climb from center vent, ( 12 degrees ) when I turn on Rear air.
It slowly drops (5 minutes).. but remains about 4-5 degrees higher than without rear air.

CuttyShark

Thanks everyone for the input. On the road, I'm about 37 degrees @ 102 ambient , fan on 2 , Rear off.

Speedtoys

Slightly low freon, or perhaps a slightly blocked front expansion valve?

Youre losing flow thru there as the rear Exp valve is now an easier path in the system...Im thinking.

dr bob

The system has the ability to move a certain amount of heat from inside the car to outside the car. The gas itself is part of the equation, minus the sum of all the heat transfer inefficiencies. Adding the rear air lets you subtract that inefficiency from total. For the differences between rear and front systems, remember that the front system is sitting inside a box with a heater core full of hot engine coolant, separated only by a plastic panel. The front system needs perfect sealing of the blend door to keep hot heater-core air from mixing accidentally with the air flowing through just the evaporator. The front system lives under a typically-black cover that also tuypically has sun loading on it (the dash and pod). The front system lives behind a metal layer that separates it from the running engine. Unless your fresh-air flap system is sealing perfectly, inlet air to the front system includes outside air that's (hopefully) warmer than the recirculating air in the car. Airflow through the front system is significantly higher that for the rear system, so while more heat is taken out of more air, the specific temperature of the air from the front will be lower.

Speedtoys

Huh. Replacing my front exp valued solved it for me.