CuttyShark

Bill: Right, I have been using zip ties for the summer, but maybe I can stop.

Wally: The condition lever; What position results in the setting motor in full cold position ?

CuttyShark

What positon would the condition lever need to be in to result in the setting motor going into full cold ?

Speedtoys

All the way to the left (except OFF)

CuttyShark

Got it all back together and working . Will road test - 2hr drive to Dallas this weekend.

Thanks all.

Herman K

Just drove from Dallas - Phoenix while it's 105F outside and my wife was inside the car covered with a blanket it's to cold for her.

CuttyShark

Made it up to Third Coast Breakfast, 102F , did improve --down to 48F at center vent but still high 80'sF inside.
Will check pressures next.

Texbuckeye

Jeff, I believe we met at the meeting. Did you meet Sean? He can fix it. Or you can pay him to diagnosis it and then fix it yourself. He really knows the 928 and he is a nice guy. Mine was doing something similar and he diagnosed the actuators being bad. He replaced them all and it blows ice cold now. I think you can Google 928Docs to get his phone number. Ignore his website it's a long story. He is a really good honest mechanic. Brad

CuttyShark

Thanks,
Yes, Sean has helped given me advice many times at meetings, and I owe him at the least, many beers.
I would take it to his shop if I lived closer to DFW-(2.5hrs.) hence I try to get done what I can at home.

In bringing everyone up to speed. Max cold is 48 out of center vent driving 2 hrs in 102 degees.
I have cleaned the evaporator, fixed acuator leaks, visually checked mix vent arm movement, zip tied HCV, checked w/ thermometer inside- did not find any temp diff from upper/lower main vent.
Today in shop with fan blowing on front condenser.
Check pressures 85F ambient,70 percent Hum., 2nd.speed fan, max cool.
At 1200 rpm;

Pressures vent floor
High Low temp temp

a) fan #2 220 15 43 72

b) Rear on 230 20 52 70
frnt #4

c)rear off 215-230 15-21 46 70

d)1400rpm 220-245 14-21 43-46 70
rear off
fan #2
Compressor never did cycle off the whole time (45min)
What does this look like? From other posts, I'm thinking I should be seeing low to mid 30's.
I saw an earlier post of too much oil in system, could it be here? low freon? Thanks.

dr bob

The freon pressures look low for your conditions. Does the drier in your car have a sight glass? A quick visual will alert you to whether you have full liquid here so the expansion valve can actually control the expansion/evaporation process. With even partial vapor (bubbles), you sacrifice cooling capacity. Of course too much pressure, that is more pressure than you need to condense the freon at current ambient conditions, means higher suction pressures at the compressor and therefore in the evaporator. That higher pressure raises the evaporation temperature and therefore the amount of heat that can be carried out of the evaporator.

CuttyShark

dr bob, thanks for the input. Yes it has a sight glass. I think I see some ripples - not necessarly bubbles as it goes over the small crossmember in the center. If I were to add freon (134a) under the same conditions, what pressures would I be looking for.
Thanks
Jef

dr bob

This is a delicate issue. The amount of refrigerant in the system needs to be adequate to keep the high-pressure side as liquid after the condenser, and no more. Anything beyond that minimum amount will bring the evaporator pressure up, which means less heat is absorbed during the boiling/evaporation process. That equals higher evaporator temps. The 'delicate' part is that the car is used in conditions that vary based on ambient conditions, car speed, engine speed, and how you have the controls set. What appears to be perfect charge on your 85º day may be less than perfect on a 100º day without the fans blowing, maybe the "stuck in idling traffic" case. Next thing to remember is that R-134a has a pretty steep pressure rise as ambient temps get above about 95ºF. If condenser airflow is reduced much (that same "stuck in idling traffic" case), the condenser pressure can spike to the point where there's a possibility of system damage. The '89 has a dual pressure switch shown in the drawing. The later GTS cars that came with R-134a native have a better switch that has separate high- and low-pressure switch connections, but that requires a different electrical connector. Integrating the later-style switch is a must for pre-S4 cars that might have cooling air flow issues, and is recommended for S4 to early GTS cars that are converted to R-134a. My recommendation anyway.

---

I was driving this morning on local city streats, with 88º showing on the dash temp display. Humid for our area at 44%, black car not heat-soaked. AC is plenty cold, and with fan on 1 and then 2, I could hear and feel the expansion valve cycling. It would open and allow more refrigerant in, and the center vent temp would drop noticeably. After a while, it would slowly pinch down on flow until the evaporator temp rose a little, then the cycle would repeat. I didn't have the thermometer handy to actually see the temp change but could feel the difference as it opened and closed to manage evaporator temperature. When your system is operating properly, you should be able to see that same TEV cycling on your gauges and on the thermometer in the vent inside. In some perect world it modulates silently and you never feel the temp change regardless of airflow or other thermal load change. Anyway, with a "perfect" charge level and varying engine speed and thermal loading, you should be able to hear the TEV changing refrigerant flow through the evaporator.

So back to your issue. At your stated conditions, I would add refrigerant slowly, until a) you see that there are just a few scattered bubbles passing the sight-glass window, .or. b) Suction side pressure gets up to 25 PSI or so, .or. c) high-side pressure exceeds 250-275 PSI. Whichever happens first. Be sure to purge your charging hoses with refrigerant as you attach them so no air is introduced during charging. And a reminder that standard "test" conditions have the engine at 1500 RPM and the cooling fans running normally. Fan speed is on 2, and you have thermometers in the center vent, on the floor, plus an ambient reading.

Speedtoys

Ive been down this path.

Its a loser.

I have a partial system of..well, unknown volume (rear AC blocked for flow, but maybe not so much for volume)...

I loaded up with R134 by the sight glass. When there were just a few bubbles left..I quit.

I ignored pressures, and I dispense ice cubes on my drive to work & back now.


I learned a LOT from RL this last month on AC.

I have gobs of R134 (30lbs can) manifold, a fantastic scale for the jug of 134, many sets of Orings for the whole car (S4 front + rear)..and will be glad to help anyone in the SF Bay Area with R134.

Bill Ball

Also, just because the heater valve is tie-wrapped shut doesn't mean it isn't leaking inside.

dprantl

If it was my car, I would recover all the R134a in the system, then charge the correct amount by weight: for '83 - '95 928's that is 860g without rear A/C or 1030g with rear A/C like Porsche specifies. If you then still have an issue, you know for sure that the correct amount of refrigerant is in the system and can go on to diagnose other parts.

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

dr bob

Just a follow-up on this particular observation (sorry...):

Oil is entrained in the refrigerant flow. Another poster used the exact word: "miscible" to describe how tiny droplets of oil are carried through. The oil doesn't dissolve. The little ripples on the sight glass are caused by oil that has dropped out of the vapor there. Key word is 'vapor'. When there is liquid flow at the glass, you might see an occasional bit of oil pass by in the liquid flow, but the flow is usually so fast that a tiny bit of pale yellow-clear oil won't be visible at all. Bottom line is that your system appears undercharged.

Repeating from previous, you MUST make your observations and measurements with the engine somewhere near the speed at which you drive. 1500-2000 RPM is good for our street-driven cars. Idle speed is too slow, and can easily cause you to over-charge if you are looking only at the sight glass. Overcharging with R-134a is dangerous to the system, particularly when ambient temps get above 95º. Condensing temps can easily be 120º+, into that steep area of R-134a's pressure curve.