Van Larson

Was losing approx 1/2 of R134a charge during summer driving season and altho this Illinois summer has been cooler than last year's nightmare, driving while chilled nicely was not a reality. Sooooo, being environmentally correct and after diagnosing a leaky evap core, took the plunge to R&R the evap and drier with the Kuehl units from Griffiths. Using the chart for pressures, ambient temps, and vent temps, the best I could manage previously was 47-53 F. and it took forever to get there while moving, not stop and go. Now, am monitoring 43-48F vent temps even while stop and go and things get more comfy noticeably faster. Not to say that you can really compare the a/c on its best day with a 13k Kia mind you but if you need to replace, feel the parts are worth it. Looking at the evap itself, easy to see much fewer joints where a leak could spring but quite surprised also how physically small they both are.

Mark in Baltimore

Good to know!

JB 911

That's the laugh of it isn't it. We need our system to be perfect in order for it to be 'ok'. You should hear the high speed condenser fan on my GMC truck it sounds like a freight train! But it cools it off, well, like a 13k Kia!

Did you DIY? The evaporator core is a pretty tough one from what I understand. Any pics or links to the one you bought?

Does your condenser fan resistor function correctly? (two speeds) have you replaced it ever before doing the evaporator? Interesting mine is out. SO it runs on high speed only, I've ordered the new resistor, but in the interim I am not driving much since I read the high speed only operation forces the system to operate under more pressure. You read any thing about that?

Van Larson

I'm now too old with a bad back for this DYI which, from all reports, seems to be a 7 or 8 on a 10 scale. Tax license. Labor parts, etc. was approx $2k. Yes, both condensers aok, but there was an engine compartment vacuum thingy with mucho "holes" also replaced. When plastic coffin containing all a/c guts was removed, it was ascertained that at least one or two cables adjusting flaps ( vacuum controlled) were AWOL as well. I keep thinking of the 70's " Rube Goldberg devices as I write this.

moeck

Griffiths is the way to go. I did mine a few years back. It's not terribly difficult but very time intensive. A good 8+ hours to take apart, then a good 8 hours to put back together. Have to drop the gas tank. I'd say it's a 6-8 level as it mostly just taking apart things to get to the evap. The parts are resonable, the labor is a killer. 2k isn't bad at all.

Rick-A-Shay

+++ on Griffiths! Their kit a "must" on my '88 for improved performance on a rather mediocre A/C.
993 still good to go.....

IXLR8

Vent temperature will depend on ambient temperatures, but unless it was ultra hot out, it looks like you are in the zone (between the lines).

I generated high pressure, low pressure and vent temperature in MS Excel in other units other than bar and degrees C.

Here is the vent temperature graph in degrees F if anyone wants to preform a check. BTW, the graphs in the Porsche Repair Manual are based on an engine RPM of 2000 and 10 minutes of operation.

IXLR8

The 3-level pressure switch will place the AC condenser fan in high speed if the AC system high pressure reaches 17.5 bar (254 psi).

As I understand it, system pressure will increase if heat isn't removed, so if your low speed condenser fan does not operate due to a failed series resistor, that condition will occur. As soon as the high speed fan comes on, system pressure should decrease and switch out the high speed fan operation...and that is where the low speed fan takes over providing it works. The AC system condenser fan should also go into high speed on very hot days, even with the low speed fan operating correctly.

Maybe Tore can confirm the above.

By the way, the low speed condenser fan operates whenever any of the two AC buttons are activated.

The other conditions of the 3-level pressure switch are system pressure too low and system pressure too high, both cases switches the AC compressor off.

JB 911

Thanks Alex. That is a handy graph.

My center vent temp was 60 yesterday with an ambient of 100. So likely will have some more trouble shooting to do after the new resistor is in. I do have a fair amount of debris blocking the condenser so I am hopeful that might drop it a few more degrees when I give it a good cleaning while I am in there.

My oil cooler resistor is out too. I usually don't plan to drive in that kind of heat, just basically wanted to see what the gauges were doing pre resistor. Did I tell you I decided I actually like the C2 bumper more now?

IXLR8

Maybe you are lacking a bit of R134a. Check with some gauges. Check also if system pressure is maintained (overnight).


I didn't check my AC condenser, but my oil cooler rad was totally debris-free. It looked like new.

Should you have lots of bugs on any of them, spray some Bug-B-Gone on them, let sit for a couple of minutes and then back flush the rads with garden hose pressure (not a pressure washer).

I take it due to ease of series resistor replacement...I thought I read something on that. As for the oil cooler resistor location...what were they thinking?

And the aluminum tin it sits on should have been dimpled out the other way so as not to pool water around the series resistor.

csmab

I measured 38 degree vent temps last week in Dallas with 95 degree temps using my infrared thermometer at highway speeds. Not sure if my evaporator has ever been changed. Stop and go is another story....not nearly as cold. If it is hot and I will be in traffic I will leave the 993 in the garage.

JB 911

Yep. Plan to do that after I get the resistors in and condenser cleaned. I havn't noticed a change in AC performance over the last few months, so hopefully a recharge will do it.

Man, that is OFF the chart! Now I have be jealous of your paint AND your AC I'm guessing that evaporator was probably changed to get those temps. That's good news - hopefully one less thing you'll have to tackle down the road.