Sure, I can test it at its normal 800 RPM idle. That is not really the standard condition to evaluate an a/c system. The idle test would accentuate the fans potential assistance, though. I was just too tired to keep at it today.
Dave

Dave could you recheck your a/c high and low side pressures @ same verified by ambient temperature
With your engine RPM at 2,000 along and your blower on low speed with your vent temps than repost them here ???

2000 RPM for an early model 911 is the “factory manual standard” for testing reading for both the a/c system and also the ignition distributor and timeing I believe

Regardless 2000 rpm is considered a good baseline rpm for your a/c compressor pressure readings and what Porsche repair shops use
ITS IN THE PORSCHE REPAIR MANUAL

I want to know what your pressures are at 2000 rpm!

@ 2000 RPM Your pressures low side will be lower and your high side should be a little higher, and I want to know what they are @ 2000 so I can try to help you better.

FYI I have done many years of 911 a/c testing @ 94 degree’s ambient here in sub-tropical Fort Lauderdale

If your truly getting the vent temps you say you are (I believe they probably are) they are GOOD FOR a static test
Your posted pressures are not bad, I like your posted high side pressure, your low side pressure isn’t bad, but should/could be lower probably with a little less
Refrigerant. R134A is very touchy to be dialed in correctly; one or two ounce high or low can make a big difference to say the least, and speaking of least; the least amount of refrigerant will give you the lowest vent temps!


I want to know what your both pressures are at 2000 rpm!???

I am going to assume 38 degree vent temp you posted is the best temp you got, but don’t know if you got this vent temp driving or not?

BIG DIFFERENCE!

Lets see if we can get your vent temps even lower/colder (grin)


However 38 degrees VENT TEMPS @ 94f AMBIENT if you get this at ALL DRIVING SPEEDS WOULD BE EXCELLENT

Excellent = ICECOLD911 3O's degree vent temps @ 95 degrees ambient
NO FREEZING UP and in all driving conditions

By the Way Dave GREAT JOB YOUR DOING On Your 911!!!

800 rpm would moreso represent a real world trial. Few of us would want to bother elevating the RPM on each occasion of need, much better to have the system fully functional in normal use.

On a side note I measured 149dF at the rear lid condenser inlet connection with guage indicating 240 PSI, high side. Looks as if 130dF thermostatic switch would do the "trick".

Also, should you still get acceptable performance at 800 RPM (38dF blower position 3, or closely nearby) it would be interesting to try using only the cabin heat blower's 120 CFM, 180 CFM with the inlet sleeve mod.

I changed my design slightly, wired the 3rd element of the trinary pressure switch in parallel with the lever heat switch. Extra fans/blower now run any time the high side pressure is above 200-230 PSI.

I would participate in testing but the weather here doesn't cooperate.

Thanks, Willard.
I have a 130 degree switch. I have not hooked it up as yet.
I will post data for 800, 1500 and 2000 RPMs. Then will try 800 RPM with various fan/ no fan configurations.
I can guarantee that 38 degree vent temps at 1500 RPM/ 94 degree OAT will translate into 45+ degree vent temps at 800 RPM (both with all 3 electric fans running.)
Dave

Didn't I recently see you calling someone a liar for stating they had those conditions?

I'm curious how well your single 964 condenser is working out. Is it adequate by itself. I just installed one and am debating about deleting the deck lid condenser.

Cheers
Nathan

You saw me call Ronnie a Liar and he is as far as I am concerned and his numbers are BS

Dave's numbers are possible and he also posted pressures

LOL. Just LOL.

Yep Eric, ole' Reid is a comedic master; he makes folks point-and-laugh in his direction with great regularity!

Hi guys,
It's been a while since I've updated this thread. I had a compressor seal leak and replaced the unit under warranty. Hopefully this will hold up. Anyway I was in the process of charging my system, today:
OAT = 84 degrees F.
High side 220 PSI
Low side 24 PSI
Vent temps 29.5 to 31.5 degrees F.
Then I noticed my High side pressure suddenly drop to 150 PSI. WTF?
It took me a moment to realized my rear condenser fans had just turned on! I disconnected them and the pressure slowly went back to 225 PSI. Reconnected the fans and pressure again dropped to High side of 150 PSI.
Now I am running dual condenser fans plus the electric engine compartment fan as an exhaust fan in the engine compartment. My idle speed is 800 RPM.
My conclusion is that rear condenser fans really do work at idle. They may not add much at higher RPMs or when moving at high speeds. The condenser fans are activated by a 130 degree F. switch that clamps onto my compressor discharge pipe. If they are not needed at speed, as evidenced by a cooler discharge pipe, the fans should shut off.
As a side note, I could not detect any rising of my High side pressure when I turned off my engine, even though it was fully warmed up. The low side started rising and the high side began to fall. They were back in the 70's PSI in 30 minutes.
I know it was a relatively cool day to perform this experiment, but that's what I got.
Thanks to all,
Dave

Hey, give Wwest a little credit!
Dave

Hi Dave,
The data speaks for itself, and thanks for closing the loop with the thread, good work....just out of curiosity you'll have 5 blowers on, 6 if a fender cond , can the alternator take it?

Love me some Willy.

Still want to choke him, on the neck, with my hands, really hard, until he can't breathe, then for another minute.......or so.

Maybe when he invites me out to Washington for a beer fest at his crib?

Great question, George. I have a digital cigar lighter voltage and it does indeed respond to the fans coming on. The alternator does seem to keep up with the fan's needs so far.
Thanks,
Dave

Dave, I've added a fan to my condenser, too, and am happy with how it seems to help speed initial cooling here in hot assss TexAss ( temps for the 10 day forecast are all above 90). I should probably get a temperature activation switch for it like you have, buttofcourse, here it would likely be activated 99% of the time.

George, I now have four fans running full time when the a/c is on and my charging voltage is at a bare minimum at idle and with the headlights on - alternator was tested at a local rebuilder and is in tip top shape. At some point, I'm going to get an aftermarket, high amperage alternator like Jim Fairman has - he had the exact situation as me and said the new alternator took care of it.

Bob has a crush on Will!!!!

Very interesting.

You were running this test with the engine deck lid completely closed, I assume?

Yes. Engine lid closed on gauge hoses, but not sealed with tape or towels.
Dave

Hi guys,
Well it's been a little over two years with my system Wwested by the addition of deck lid condenser fans. It has been performing very well. So much so that I no longer carry a thermometer to measure vent temps. The car has been comfortable through the past two Chicago Summers.
Anyway, I was fooling around setting my base idle speed, so I had the deck lid up and let the car run for 10-15 minutes to come to operating temp. I did my adjustments, and noticed that my compressor was cycling and my car interior was very cool since I left my a/c on.
That was with the deck lid up!
Now it's only 86 degrees in Chicago today, but that does tell you that the fans move some serious air and the a/c does not depend entirely on the engine cooling fan. After all the condenser fans were only there to supplement cooling at low engine speeds. You can't get much lower than functionally out of the condenser airflow.
Have a good Summer,
Dave

Would love to see the results in 100°+.

It's 86 by 9AM here in Central Texas... ;)