Factory AC pressure switch details

[MConn]

I have an 87 Targa that does not have a high pressure switch (I popped the condenser with the trunk lid up - newbie mistake), and am working through the AC on a newly acquired 88 coupe. The coupe was made in 11-87.

The Bentley Service Manual for the 1984-1989 Carrera shows an AC high / low pressure switch in series with the clutch in the electrical schematics for the 1988-1989 model years on page 970-51. Bentley does not show a switch on the 1986-1987 model year on page 970-49.

Questions:

When did the factory begin installing pressure switches on AC systems? (start of 1988, mid year 1988, etc…)

Where was the switch located?

What is the part number for the switch?

What pressures did the switch operate at?

Thanks for any information.

Mike

[kuehl]

Mike,

You are probably referring to the ac schematic below,
found in the shop manual.

Porsche never incorporated the pressure switch in the
911 or 930. You can assume that 'someone' in their
engineering group decided to sneak it in during the afternoon
beer break but manufacturing or the bean counters voted
it down.

The water cooled group did have pressure switches (924s, 928, 944/951)
back in 78 (928) onward, however the air cooled group did not.

Pressure switches on air cooled models started with the introduction
model 964 AWD in 1989 and all air cooled models moving forward.

You can add a 'binary' (low pressure/high pressure) switch to the system
typically at the outlet side of the compressor, between the compressor's outlet port and the rear deck lid condenser. Typically we include this feature in our barrier hose assembly for the compressor to deck lid condenser. Or, you could attach one to a
"T" connection on the compressor's high side service port (this is a bit of PITA if you also need an R134a adapter with it), or in a T on the compressor outlet port.
We prefer the feature built into the barrier hose assembly. One wire lead connects to the AC power supply terminal by the oil filter and the other lead connects to the compressor's clutch lead.

These switches are 'automatic' plug and forget devices with pre-determined on/off settings. The low side feature cuts off the power to the compressor should the pressure in the system drops below a specified psi, and the high side cut out feature cuts off the power should the pressure rise above a specified psi. When the pressure returns to min or max values the switch resets itself and power is restored. PSI values vary between mfg's models, however, for example, the low side could be below 16psi and the high above 345 psi... for example.



Read the Mr. Ice Project

[wwest]

Originally Posted by MConn

I have an 87 Targa that does not have a high pressure switch (I popped the condenser with the trunk lid up - newbie mistake), and am working through the AC on a newly acquired 88 coupe. The coupe was made in 11-87.

The Bentley Service Manual for the 1984-1989 Carrera shows an AC high / low pressure switch in series with the clutch in the electrical schematics for the 1988-1989 model years on page 970-51. Bentley does not show a switch on the 1986-1987 model year on page 970-49.

Questions:

When did the factory begin installing pressure switches on AC systems? (start of 1988, mid year 1988, etc…)

Where was the switch located?

What is the part number for the switch?

What pressures did the switch operate at?

Thanks for any information.

Mike

A good source for an R-134a adapter set, binary pressure switch, and as I most heartily recommend, a trinary pressure switch.

A/C Pressure Switch

The extra function of the trinary pressure switch is typically used to power a fan to more adequately cool the condensor should the system pressure rise high enough. In our case that would be the front lip fan/blower. Unless you decide to add additional cooling fans for the engine lid condensor as I, and a few others, have done quite successfully.

There is, of course, an aftermarket alternative...a fender mounted condensor/fan assembly. The fan itself be the major contributor to the need for additional cooling capability at times when the engine fan(consisetntly low engine RPM) along with the front lip fan proves to be inadequate.

"BASE" logic, and information from the EPA and the SAE, indicates that our non-barrier hoses should NOT leak even with the higher pressures entailed with an R-134a conversion. So, something other than, or along with, the hoses themselves MUST be the causative factor.

Due to the higher pressures running R-134a the EPA requires the additional use of the pressure switch, and for taht and other reasons even Kuehl has signed on to this.

So I recommend that you not only use the trinary switch element to power condensor cooling fan(s), but provide for "after-run" with a connection directly to the battery.

The 996 & 997 series, water-cooled, has "after-run" provisions for cooling the engine compartment long after the engine is shut down. There is an ECU that checks the engine compartment temperature on a periodic basis post engine shut down and if it rises to the "trigger" setpoint the engine compartment cooling fan will be powered.

So, to what level might our engine compartment temperatures rise....and what about the engine lid condensor already filled, fully filled, with liquid refrigerant at OAT but now to rise due to the loss of cooling airflow, rising convection HEAT, and the always present radient heating effects.

Enough to pressurize the system well beyond the non-barrier hose design specifications..???

[kuehl]

Originally Posted by wwest

So, to what level might our engine compartment temperatures rise....and what about the engine lid condensor already filled, fully filled, with liquid refrigerant at OAT but now to rise due to the loss of cooling airflow, rising convection HEAT, and the always present radient heating effects.

Enough to pressurize the system well beyond the non-barrier hose design specifications..???

So, have you proven this theory?

Originally Posted by wwest

The extra function of the trinary pressure switch is typically used to power a fan to more adequately cool the condensor should the system pressure rise high enough. In our case that would be the front lip fan/blower.

The front condenser's blower motor is already controlled by the present OEM circuit. It works!

[MConn]

Originally Posted by kuehl

Mike,

You are probably referring to the ac schematic below,
found in the shop manual.

Porsche never incorporated the pressure switch in the
911 or 930. You can assume that 'someone' in their
engineering group decided to sneak it in during the afternoon
beer break but manufacturing or the bean counters voted
it down.



Read the Mr. Ice Project

Thanks Kuehl.
Thats exactly what I was looking at, and wondering where the factory hid it. I'm trying to 'get by' this year with the factory system, but I have your front condenser and dryer on my project list for next year. Surprisingly, my original hoses are in good shape and held vacuum for 24 hours before charging. If my hoses remain tight this year, do you offer a Tee fitting to add a high pressure cutout swith at the compressor? The car never was converted from R-12, and I'm trying R-420a that my AC buddy likes, so I'm not sure that R-134a conversion is in my future.

Mike

[kuehl]

Mike,

The original non barrier hoses permeate refrigerant the day they came out of the factory,
vacuum is different world. Best to buy new barrier hose assembly (compressor to deck lid condenser with the switch built in) because sooner or later the original factory hose
leaks from heat, vibration and age.

[wwest]

Originally Posted by MConn

Thanks Kuehl.
Thats exactly what I was looking at, and wondering where the factory hid it. I'm trying to 'get by' this year with the factory system, but I have your front condenser and dryer on my project list for next year. Surprisingly, my original hoses are in good shape and held vacuum for 24 hours before charging. If my hoses remain tight this year, do you offer a Tee fitting to add a high pressure cutout swith at the compressor? The car never was converted from R-12, and I'm trying R-420a that my AC buddy likes, so I'm not sure that R-134a conversion is in my future.

Mike

Should you enrich Kuehl at any level it should be, first, for the fender mounted condensor/fan assembly. I suspect Kuehl might agree.

Plus, haven't I seen Kuehl state that their front lip condensor is less effective than the factory one?

Absent adding the pressure switch to prevent the compressor from over-running, thus over-pressurizing the system, you WILL experience a loss of refrigerant. Enough, over a 2 year term (at best) to adversely affect the A/C adequacy. If my theory proves to be correct you will not only need the binary switch functionality, but the trinary function to provide "after-run" capability for the front lip blower/fan, or even the fsan in the fender mounted condensor/fan.

Absent a conversion to R134a a dryer change over would be worthless. I have my doubts even "with".

[wwest]

Originally Posted by kuehl

Mike,

The original non barrier hoses permeate refrigerant the day they came out of the factory,

There can be NO question that system pressure plays a very significant role, perhaps the MAJOR role, in the "permeation" rate of our legacy "non-barrier" hoses. Will replacing them with newer "barrier" hoses eliminate the problem...??

Yes, no question, well proven solution.

But what if we could limit the pressures that result in our legacy hoses leaking???

Not proven, but logic and the evidence indicates a positive result is likely.


vacuum is different world.

Vacuum is NEVER present in the operational mode of our systems.

Best to buy new barrier hose assembly (compressor to deck lid condenser with the switch built in) because sooner or later the original factory hose
leaks from heat, vibration and age.

"...sooner or later.." Possibly a LOT later, tens of years maybe...

[wwest]

Originally Posted by kuehl

So, have you proven this theory?

Just what is it about three question marks, "???", that you do not GET..???

The front condenser's blower motor is already controlled by the present OEM circuit. It works!

Yes, it runs FULL time when the A/C is enabled. Using the trinary switch to control it would result in it running only as necessary and could also allow it to operate post engine shutdown should system pressures warrant.

[kuehl]

Originally Posted by wwest

Should you enrich Kuehl at any level it should be, first, for the fender mounted condensor/fan assembly. I suspect Kuehl might agree.

Read the Mr. Ice Project

Originally Posted by wwest

Plus, haven't I seen Kuehl state that their front lip condensor is less effective than the factory one?

Oh, it is.

Kuehl Serpentine Front Condenser


[/QUOTE]

[MConn]

Originally Posted by wwest

Should you enrich Kuehl at any level it should be, first, for the fender mounted condensor/fan assembly. I suspect Kuehl might agree.

Kuehl's front condenser is priced competitively on our hosts web site against another well known brand. Please provide me with the link to your product line, so that I may evaluate your products as well.

One point we should NOT forget -
Unless we enrich our host (buy some stuff), this forum will not exist.

Mike

[wwest]

Originally Posted by kuehl

read the mr. Ice project

yes, but pay special attention to the first line of every comment in the "customer comments" section.

Oh, it is.

kuehl serpentine front condenser

less effective..?

[/quote]

...

[wwest]

Originally Posted by kuehl

Read the Mr. Ice Project



Oh, it is.

Kuehl Serpentine Front Condenser

[/QUOTE]

You should take note that Kuehl's front lip condensor has a rather serious design flaw vs the factory design in that it actually BLOCKS the natural airflow due to forward motion of the vehicle.

[wwest]

Originally Posted by MConn

Kuehl's front condenser is priced competitively on our hosts web site against another well known brand. Please provide me with the link to your product line, so that I may evaluate your products as well.

I have nothing to "sell" other than knowledge.

One part of snake oil being priced competively with another...

No one disputes as factual that the major shortcoming of our Porsche A/C is the lack of sufficient refrigerant cooling, condensing, efficiency. Simply adding more efficient condensors does NOT address the core issue (lack of cooling airflow) and as such should be seen as marketing SNAKE OIL.

One point we should NOT forget -
Unless we enrich our host (buy some stuff), this forum will not exist.

Mike

Yes, we should all strive to enrich, and thus thank, our host. But not, NEVER, to the extent of purchasing SNAKE OIL, Pro-Coolers, for instance.

[kuehl]

Originally Posted by wwest

You should take note that Kuehl's front lip condensor has a rather serious design flaw vs the factory design in that it actually BLOCKS the natural airflow due to forward motion of the vehicle.

Actually Wwest,
the Kuehl unit allows more air flow because of the spacing of the serpentine tubes and
cooling fins.

[wwest]

Originally Posted by kuehl

Actually Wwest,
the Kuehl unit allows more air flow because of the spacing of the serpentine tubes and
cooling fins.

Yes, when the electric fan is the major, or only, cooling airflow source. But at roadspeed the vertical orientation of the fins BLOCK most of the cooling air resulting from roadway speed.

Look at the cooling fin/vane orientation, arrangement, of the factory front lip condensor for comparison, open to BOTH vertical (fan) and horizontal (roadspeed)cooling airflow.

[kuehl]

No Wwest.
With our condenser, because of the design, it out performs the OEM and competitors.
But, since you never work on Porsche AC, you have never designed a condenser or any other component for a Porsche, and the Lexus you constantly refer to does not qualify,
you'd never know would you (that last two words are rhetorical so you don't have reply).

[wwest]

Originally Posted by kuehl

No Wwest.
With our condenser, because of the design, it out performs the OEM and competitors.
But, since you never work on Porsche AC, you have never designed a condenser or any other component for a Porsche, and the Lexus you constantly refer to does not qualify,
you'd never know would you (that last two words are rhetorical so you don't have reply).

See, that's what I mean when I call you out for selling SNAKE OIL.

You VERY well know that an investment in a fender mounted condensor/fan combination would dramatically overshadow an investment in ANYONE's front lip condensor.

Yet you continue to push...SNAKE OIL.

And any IDIOT could judge your front lip condensor design flawed with a just a quick look.

"..you have never designed.."

Design experience is not a necessaty for gaining knowledge.

[kuehl]

Wwest,

Again, your lack of experience is amazing considering how many threads you post on.

But, since you always have such positive things to say about our products, as well as my comments, I might was well just ride the little SEO wake you have made.

Yes, our Kuehl Fender Condenser with fan certainly does blow away just the front serpentine condenser. However you are not comparing apples to apples.

Whether a 911 or 930 owner needs just a better front condenser, or
the Kuehl Fender condenser or a combination of the 2 or more all depends
on several factors.

But, in the mean time, I think your exhaust has fouled up this this thread enough for any readers enjoyment.

Thanks ror the wake dude!

[tirwin]

I guess it's just impossible to discuss this topic anymore.

Maybe the rest of us can take up a collection to benefit some charity (hey, some good should come out of this, right?) to sponsor The Great Air-cooled Porsche A/C Shootout. Start with stock cars and let Keuhl, Wwest, KelogGes and any other contenders do their magic. Prize awarded for the best performing A/C at the lowest price. The prize is the others have to shut their pieholes and the Porsche world gets to live in peace.

Outside of that I think this will continue ad infinitum.

PS - of all the topics that people could argue over I never though it would be this. Why is that? Is it too subjective? Lack of empirical evidence? I don't know...