Damian in NJ

Just curious; one of the Wilhoit 928's in the classifieds has this listed as an option, as well as another 928 I've seen.

I've never seen any other Porsche model with this option-was this solely for 928's? And what did it consist of?

James Bailey

The added cooling unit between the rear seats with its own blower it borrows "freon" from the main system.

Alan

An additional rear AC unit (evaporator) running off the same front compressor loop - so otherwise known as Rear AC. It has no external air feed so its a re-circulation system only. It also strangely is not tied in any way to the automatic temperature control function of the front AC and has no heating mode at all.

Alan

Randy V

Porsche introduced this additional cooling due to the 928's expansive glasswork and resultant greenhouse characteristics.

The additional cooling is not significant, as there is reduced cooling from the front system when the rear system is also running. For that reason I never run the rear system except on occasion to keep it functioning.

James Bailey

Perhaps some Saudi Princess found it to be a bit warm sitting under the rear glass and requested a fix ? Which Porsche said they could do no matter how much it costs

Damian in NJ

I knew you guys know your stuff, thanks.

jayc67

I use mine often in Texas summers. It does reduce the output of the front cooling but it seems to cool the overall interior temperature quicker rather than have a cool spot in the front. Also, if you point the 4 vents forward you get a nice cool breeze from behind your head which can be nice.

And if you ever DO put someone in the back seats, they love it.

borland

Maybe Randy's GTS is rear AC is reduced cooling, cause the GTS machines are all running R134a, while the earlier cars came with the more efficient R12.

The rear AC is controlled by the console controller/panel, in that there is a temperature setting **** for the rear AC, and also an electrically activated refigerant flow control valve under the front passenger seat.

Ninespub

Yeah, I've never used it in 91/2 years and I just can't seem to get confirmed (sucessfull) instructions how to delete the rear air without pulling the block. Anyone got a response? (ooops) I really didn't intend to hijack this thread, I was venting with a rhetorical question and it kinda seems that way.
Paul Barrera '91 $$$$4

dprantl

The right way would be to remove the hard A/C lines and replace with non-rear A/C versions that don't have the T-ed line going down and back to the rear evaporator. This would almost definitely require pulling the engine. Or, you could just cut the pipe off at the T and seal it up, preferably by brazing. Then, just rip out all the other rear A/C stuff and put that "map box" back there.

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

FredR

I understand the valve under the seat is a solenoid operated valve - i.e. it is on/off rather than modulating. The **** on the front panel modulates the fan speed to achieve some modulation of heat transfer.

The observations about "robbing Peter to pay Paul" are spot on. I believe the first limit to the system capacity is the condenser sizing. For this reason manual tranny models work better because they have a bigger condenser surface area. If you want to improve the a/c system first step is intall [good] heat absorbing film on the windows- especially the green house at the rear- trust me- it really works.

Unless you have kids sitting in the rear two seats then the rear a/c option is not really worth it.

Regards

Fred [46C here in summer!- very nice now [22C this evening]

ROG100

Just for the record - the 92/early 93 GTS's are R12.
Later 93 cars and on are R134a and run very very cold.

Gary Knox

I agree with Roger about the 134A in the '94+ cars. My '94 runs colder with or without the rear AC on than any of the five S4's I've owned. At 'mid to high '90 degree temps and highway speeds, I have both the F & R set to about 68 degrees, and the fan on the lowest setting for comfort in the '94.

Gary

docmirror

If the size of the condenser is the same on rear AC cars, the total cooling capacity will not be improved. I don't know if they use the same condenser or not. The condenser size determines the cooling capacity of the AC system, not the evap(s).

FredR

Gary,

For reasons I have never understood, the cooling curves in the workshop manual suggest the 134a performance is superior which contradicts what most people appear to say.

My 92 GTS is identical in all respects to the a/c shystem that was in my late S4 insofar as I can tell. I recently tried converting the system to 134a for trial [did not replace to barrier hoses] and found the performance with 134a was not as good so reverted to R12 which is still available here but not for much longer.

From your post and one of the earlier ones- it sounds as though your [later] GTS has the ability to select temperature on the rear a/c so my earlier note may only apply to my model year [i.e. 92 and early 93 GTS's].

Regards

Fred