The Brewmeister

I would like to introduce everyone to my 1988 911 Cabriolet with 87,000 miles. Unfortunately this car came to me at a heavy price. It belonged to my brother in law who passed away from a rare form of cancer at the age of 50. It was his wish that this car would go to me. After 2 1/2 years in and out of shops and some of my own work it's finally coming together! It's been a long hard road and a considerable amount of money has been spent.

Highlights include:
-Fuchs are back on the car with Michelin Pilot Exalto PE2 tires
-European ride height
-New top
-New driver and passenger seat upholstry
-Porsche CDR-220 Radio-CD player and Blaupunkt speakers
-New Lloyd floor mats
-The hood, front bumper, front valance, mirrors, rocker panels were all repainted. The rockers had been damaged and poorly repaired with bondo (they were smooth and the surface was checking).
The hood was checking also. The other parts were just showing their 87000 mile share of stone chips and the like. The drivers door had a significant ding and dig (and poor touch-up) that required a repaint as well. The rockers and front valance were both refinished in the proper "stutz" textured finish.


One outstanding issue is the AC. It won't hold a charge for more than a year.
The fact that the car is a Cab has me on the fence about whether a major AC upgrade is worth the money. If I do it, it probably won't happen until next Spring.

The "before" and "after" pics are very obvious.

Reiver

Looks like a nice set, sorry abt the BIL, good luck with it.

Amber Gramps

Wow, Allen. She looks great. I happen to like '88 cabs. Sorry about your BIL.

Any further plans?

tulliotk

Looks kinda familiar. I like '88 cabs, too. I also inherited mine. My car was my father's.

tulliotk

Like this:

ECS Tuning

The car looks great It's coming together very well, and your brother in law would be proud.

BigMikeATL

Driving a cab multiplies the Porsche driving experience to another level. Nice car!

I'm loosely looking for a '70 Mach 1 to restore in memory of my older cousin Don, who died 2 years ago of a rare bone cancer. He used to tolerate me as a kid hanging around his cool cars and bikes and let me help him do things. He is the main reason I because such a car enthusiast.

wwest

1988 Carrera Special Edition.

I have long been of the firm belief, and remain so, that refrigerant leakage in our Porsche's is the result of a design flaw on the part of Porsche. Many naysayers will chime in and attempt to convince you that the problem lies solely with the use of non-barrier hoses. But many other marques of this era made use of these very same non-barrier hoses and yet hold their refrigerant charge intact for decade after decade.

So what, then...?

Inadvertent over-pressurization, high side pressurization well beyond the 350-450 PSI that appears to be an acceptable high end pressure for A/C systems of this era.

Why, how....?

Many systems of this era used a HPRV (BOV), a vent to atmosphere pressure relief valve (***1) should the high side pressure exceed the normal pressure range. In the alternative some systems of this era used a high side pressure sensing switch to disable the compressor clutch once system pressures reached 350 PSI.

Some even used both...

(***1.) Yes, R-12 VENT-TO-ATMOSPHERE....!!! Even in my 1992 Ford AeroStar...

Why make use of both provided the pressure switch prevents the compressor from forcing the high side pressure from being excessive...??

Because there is MORE to the equation.

Suppose the compressor has just driven the pressure to the limit, 350 PSI, but now you switch off the ignition...?? Now you have just disabled the airflow that was cooling the rear lid and front lip condensers, keeping the high side pressure "in check", against the CONSTANT engine/exhaust radiant heating, as it were. Loss of cooling, now NOTHING to compensate for engine/exhaust RADIANT heating of the rear lid condenser, the high side pressure will undoubtedly begin to rise.(***2)

In my simple (simpleton?) test to prove my theory out the temperature of the rear lid condenser fins/vanes rose for 120F with the A/C FULL on, engine running at idle, to ~150F within just a few seconds of switching the engine off.

More to the equation.....engine and exhaust manifold HEAT.

Even without the rear lid condenser being problematic Porsche engineers recognized the problem in the 964 and 993 series, and yes, even in our 996/997 cars.

With the 964 came a new design aspect that helped to prevent the engine compartment HEAT from rising too high in certain conditions. With extended idling, say iwith consistent, prolonged, rush hour stop and go driving, if the engine compartment temperature, convection + radiant, exceeded 70C the cabin heater blower would be powered on to help "wick" the exhaust manifold HEAT away from rising up through the engine cooling fins/vanes.

The new design aspect also included an "after-run" engine compartment cooling capability. If, as you switched off the ignition, the engine compartment temperature was above 30C then a 15 minute time delay circuit was "armed". Now, for the next 15 minutes, if the engine compartment temperature continued to rise and reached 70C the cabin heater blower/fan would be powered. Again, to wick away the exhaust manifold heat and discharge it into the rear wheelwells.

(***2.) For purposes of this dissertation lets assume that as we switch off the ignition the A/C evaporator core is already at ~33F, thus the TXV is mostly closed, the R/D is filled with seevral ounces of liquid refrigerant. And with no air being forced through the evaporator cooling fins/vanes it might take many minutes for the R/D's liquid refrigerant to be "exhausted" and then for the high side and low side to begin equalize. More than 20 minutes according to Charlie at Griffiths.

Sidebar: Google..

Bob Tindel cooling

Solution for leaking non-barrier hoses.

Tape and insulate a thermistor to the metal pipe as it enters the rear lid condenser. Use the thermistor value to discern if/when the high side pressure exceeds 300 PSI. Once 300 PSI is sensed then power the cabin heater blower/fan. Should the sensor indicate >350 PSI disable the compressor clutch circuit. Ignition on or off, POWER the cabin heater blower/fan as long as, whenever, the sensor value indicates >300 PSI.

This will not only prevent the loss of refrigerant on a 1 or 2 years cycle, it might well rise the overall A/C system performance to a more adequate level.

With the engine idling at ~800 RPM I meaured ~100 Ft/m airflow at the center/top of the rear grille, with the cabin heater blower powered it went to ~200 Ft/m. Single point measurement, no attempt to calculate overall inlet airflow.

The Brewmeister

The Porsche AC system for cars from this era was at best an add-on. They placed the condensers in the only places they could to get air flow over them. My Porsche Indy no longer uses R-12, the cost is prohibitive and the regulations for it's handling are ridiculous. The system was retrofitted for R-134 and that doesn't help with the efficiency factor. Upgrades are expensive which I'm well aware of. Is it worth it for a Cab? Or when it's hot just take the 993?

The Brewmeister

Your Cab looks nice. How many miles?

tulliotk

Around 130K miles. My dad had it since new.

The Brewmeister

^ Your dad must have taken great care of it. It shows neither it's age or mileage.

tulliotk

He did have it repainted a few years back. It was his daily driver for a number of years including through Chicago winters!

PelicanParts.com

Beautiful cabs, both of you!

Alan, certainly is a special tribute to your late brother-in-law! Nice work.

The Brewmeister

^Thanks, and parts from you guys helped! You have helped with the 993 as well!