Yes, Told him exactly what I had in mind and he thought it would be fine. BTW my condenser is brand new OEM Porsche at $750 vs non-OEM's at $300 (mechanic could not find one with fittings that lined up properly with hoses & brackets). Hopefully, the price is indicative of a better quality and will hold up better.

It's sort of a moot issue now but the strengthened, triple pass 911 condensers Scott's Performance Aire sells look a lot like that OEM one; they're ~ $450 each:

http://www.scottsind.com/Navigation/MastercraftAC/Mastercraftacframe.htm

Installed Performance Aire 911 aftermarket condenser:

http://forums.pelicanparts.com/uploa...1162955663.jpg

Fan Project Update:

Well, I worked on the fan project today. Unfortunatley, I was a little too ambitious in my planning and was only able to fit one of three fans on the condenser. Not enough clearance above the heater tube or the alternator fan shroud :( .

I'm going to play around with it some more and may get one addl fan to fit...or order a smaller fan to fit above the alternator. No clearance above the heater tube at all.

In any event, the fan mounted easily with the nylon push throughs, although it was necessary to unbolt and lower the condenser. I installed a relay in the engine compartment to control the fan and wired it to the A/C compressor to turn the fan on and off automatically whe the A/C is running.

Wiring of the fan was a b*tch because of errors on the wiring diagram that came with the relay but I was able to get things figured out after a lengthy troublshooting process.

The spal 7.5 "pull" fan that I used is rated at 440 CFM. I was pleasantly surprised with the amount of air that it moves! I think this is going to be a great addition to the A/C system.


Nylon push through ties worked nicely.
http://forums.pelicanparts.com/uploa...1171944170.jpg

Had to remove center fan after test fitting
http://forums.pelicanparts.com/uploa...1171944287.jpg

Very clean & easy installation
http://forums.pelicanparts.com/uploa...1171944363.jpg

Fan relay...pic is before I connected power through the lower fuse (rear wiper/ defroster 25 amp fuse)
http://forums.pelicanparts.com/uploa...1171944516.jpg

Follow-up. Fan working nicely. Very faint fan motor noise can be heard in the cabin - positive feedback that it's working :D

Considering adding a TDR to allow the fan to run for a minute or two after shutdown to assist engine cooling. More here:

http://forums.pelicanparts.com/showthread.php?s=&threadid=31134&highlight=time+de lay+relay

(BTW, it's an old post......Scott has sold his 911 and no longer has the wiring diagram)

Mark,
Installation looks clean. Congrats.

"Considering adding a TDR to allow the fan to run for a minute or two after shutdown to assist engine cooling. "

RE: to piggyback on your timer idea. Since heat normally rises, I think it'd be more efficient to reverse air flow after shutdown. Since the fans are powered by a DC motor, they are potentially reversible by changing polarity (+&–) - check w/Spal. That way, the fans can help evacuate hot air from the engine much like most imports continue blowing air over the radiator after engine OFF. I'm pretty sure they use a thermal relay rather than a timer.

FWIW,
Sherwood

Fans on the rear condenser do help a lot. I did an A/C installation several years ago. Do a search on my name.

Contrary to popular belief the engine fan doesn't move very much air. As I recall max air velocity through condenser is <5 mph with engine fan alone.

Hladun, I think this is the post you are referring to.

http://forums.pelicanparts.com/porsche-911-technical-forum/61620-74-911-c-upgrade.html?highlight=fan

Reading through it reminded me that on my install, I did have to remove the airbox horn in order to get my fan to fit. Did some more measuring tonight......no way to get another 7.5" fan to fit on the underside of the condenser, BUT, I think one or two 4" fans will clear the alt fan housing and heat duct.

http://www.spalusa.com/fans/automated/motorcycleatv_4_paddle.html

At 124 CFM each, the addition of two 4" fans would increase my supplemental airfow to 688CFM from 440CFM - an increase of 56%! As I sit here remembering sweating my a$$ off last summer before getting my system functioning, this sounds encouraging. I was and still am obsessed with improving the performance of the stock A/C system.

Here's a picture of my installation:

http://forums.pelicanparts.com/showthread.php?s=&threadid=244487&highlight=AFC+fa n

Keeps car cool in 90F+ with no other condensers.

OK, after remeasuring and test-fitting I can add one addl 5.1" fan (313CFM) and one addl 4" fan (124CFM) to my rear consenser bringing the total CFM up to 877 - an increase of 100% over the single 7.5" fan.

Ordered new fans yesterday. I've now got two extra 7.5" fans rated 440CFM from my original plan that I'm not going to use. I'll let them go for $40/shipped (each) if anyone is interested. (I paid $53/each).

Looking forward to a cooler summer!!!!!!!!!!!!

Mark, save one for future replacement of the front oil cooler fan.
And I'll take the other.

Derk, good idea on saving the fan to relpace the oil cooler fan. Finally heard it kick in in a traffic jam last week - nice to know it works. I gotta think the Spal moves more air than the OEM cooler fan.

Just sent you a PM on the extra fan.

I did the exact same thing, except I added 2 fans. My mechs have said time and time again that they can't believe how cold a stock AC can be. Well it's not exactly stock, but it really does work.

Here was my thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/235096-i-did-too-pro-cooler-mod-my-c.html

Project Update:

Received the two addl fans for the rear condenser and a time delay relay last week, but, due to an evap freeze up - I got a little distracted this weekend and diverted my attention to cleaning the evap coil and box and added one of the new fans to the passenger floorboard as a blower assist at the evap intake port/resistor pack. Details here:

Thread:
http://forums.pelicanparts.com/showthread.php?s=&threadid=336402&highlight=assist +fan

Got vent temps of 34-35 today with rapid temp drops when the compressor, rear condenser fan and evap assist fan were all running - AT IDLE. I realize that the true test will be at ambient temps of 90+ sitting in traffic (not too far away) but the initial results are encouraging.

I've now got to order another 4" spal fan to replace the one I used in the footboard. The 5.1" and 4" fans yet to be added to the rear condenser will move an addl 427CFM to the 440CFM already installed.

I'm never giving up!:D

Couple of pics with two fans installed (7.5" and 5.1"). I'm holding off on the third for now since the system is working so well after cleaning out the evaporator and adding a fan to the evap intake in the passenger footwell.

Link to my performance results to date here with encouraging vent temp data:

http://forums.pelicanparts.com/showthread.php?s=&threadid=338407&highlight=vent+t emp+update

http://forums.pelicanparts.com/uploa...1175555266.jpg

http://forums.pelicanparts.com/uploa...1175555352.jpg

Mark: Maybe I missed it earlier in this long thread, but are your fans "pushers" or "pullers?" I'm guessing "pullers" since you'd want them to work in sync with the engine fan, but I'm checking to be sure.

Nice work!

Scottb, you are correct, they are pullers.

Thanks!

sub'd. good thread for those of us in the humid south

I recently routed a 10 ga. + to the back via the a/c lines under the driver's side. I went into the cabin through an existing grommet, then out the upper door jam grommet, finally down and through the rocker. Since this car is running relays on the headlights, fan booster, and some other stuff, I ran a fuseable link wire to a central terminal up front by the fuse box. From that point, I pull to the various components that are relay operated, including the rear power supply. All power lines begin with another fuseable link.

It's nice to see that the solution I proposed more than 5 years ago is now gaining popularity. You just can't beat A/C on a hot day and it's a shame that for 20+ years the solution was to tear the system out and sweat!

mthomas58,
I wonder if you can get 7.5" pusher fans and install them on top of the condensor? Assuming you have whale tail.

HELP!! Power from the rear fues box?
I looking for how to wirie the relay and power for the fan. can anyone provide a diagram of how they did it ?
or a point to point wiring direction.

I had a helluva time getting the relay wired properly....lots of trial and error. I'll take a look at the wiring tomorrow and post a diagram.

I have been meaning to diagram the relay wiring for my records since it was such a cluster getting it wired up. Had help from a neighbor and father-in-law on the phone (engineer) to consult. In the end, I wasn't clear on what we had actually done! Anyway, here is how we wired the fans. Hope this helps. Once I get everything finished (may add one more fan and swap out relay for a time delay model) I'll clean up the wiring with some shrink tubing and wire ties.


http://forums.pelicanparts.com/uploa...1178458849.jpg

Blue power lead from fans directly to fuse block. Red wire from Relay pin 30 to fan ground wire. Orange wire from Relay pin 86 to A/C power lead (triggers relay only - does not power the fans). Center pin is 87a and is unused:

http://forums.pelicanparts.com/uploa...1178459246.jpg

Orange wire from relay pin 30 connected to green A/C power lead via snap-on wire tap/splice

http://forums.pelicanparts.com/uploa...1178459612.jpg

I have 2 Fans mounted as per picture. am I to understand this is not a factorystandard addition?

http://forums.pelicanparts.com/uploa...1178476054.jpg

dralph12,

The way mthomas58 installed it looks diff from what I did. I am not sure which way is better or they are the same but my fan always get (-), relay supplies the (+). The below method I got from gathering info on this board on how to use relay.

85 to ground (car chassis).
30 to batery (+) terminal.
86 is the turn-on-signal wire (+). Can be connected to a switch or any source. In this case should be the AC compressor?
87 supplies (+) to fan (+).
Fan ground is to engine lid.
87a no use.

Thank You!!
I will get mine wired up in a few weeks and post my Pic's.
I am replacing the rear deck lid condenser. I found a guy that manufacturers condensers.
My OEM condenser has 8 rows of tubing, his will have 12 rows of tubing in the same
space " smaller tubing = more surface cooling area" I will post these pic's soon.

Dralph12, check out Mysterytrain's post here.....this is a better way to wire the fans. I'm going to rewire mine accordingly.

http://forums.pelicanparts.com/porsche-911-technical-forum/345085-rear-c-condenser-fan-relay-wiring-diagram.html

Here's a generic schematic of a 1M-1B relay, Bosch-made or otherwise. The terminal numbers are DIN spec, meaning all DIN-spec !M-!B relays adhere to this terminal ID standard.

Typically, there are two circuits; the power circuit (terminals 30 and 87) and the control circuit (terminals 86 and 85).

http://forums.pelicanparts.com/uploa...1178571758.jpg

Terminal 30 connects to source voltage (from the battery or equivalent). 87 leads to the load (condenser fan motor).

Terminal 86 connects to a switched source circuit to chassis ground via 85. When the control circuit switch closes, current flows through the relay coil which causes the contacts to close and complete the 30/87 circuit.

The 87a terminal is there in case a circuit designer wishes to use the control circuit to open the normally closed circuit through 30/87a.

While any relay can be located on either side of the load (fan motor), it's more Japanese-style to place the power side of the relay (30 -> 87 circuit) on the ground side of the load. The theory is that voltage is reduced on the ground side of the load thus less wear on the relay contacts.

Japanese style:
Bat. -------fuse--------> fan motor------>30 relay 87 ---> ground.

DIN-style:
Bat. -------fuse--------> 30 relay 87 ---> fan motor------>ground.

Sherwood

Ok I wired up my rear A/C condenser fan, but havent done the time delay relay yet.
Here is my issue! fan works great and my AC is under 50 Deg. at the vent but when the AC and Fan are on there seems
to be to much of a load on the alternater. My Tachometer goes nuts and the other gauges start bouncing around.
In fact I know the load is to much becouse I took the car out for a nice drive with the AC on and I needed to charge the battery when I got home. I have been having this issue before I added this fan. It started when I added the first fan to the Oil cooler. I know when the battery needed to be recharged that both fans were on "AC and Oil cooler" I hAVE CHANGED THE ALTERNATER and the Battery but
Im still having the problem. this happend only then one of the added fans are on. Any idead? HELP!!

Third fan finally installed today!:D

http://forums.pelicanparts.com/uploa...1182704202.jpg

Is there an advantage in using three fans vs. two of the large ones? Current load vs CFM air flow?

Sherwood

Sure would be interesting to see some data acquision runs on alternator heat sink temps, head temps, cylinder temps, oil temp at scavenge line outlet port ... before and after the install of such large restrictions to the air flow into the engine fan??? My estimate is that you could raise oil temp 10°F - 20°F with such an install. Maybe a cool collar to offset the increase?

I was limited on fan size due to my choice of mounting pullers under the condenser with clearance restrictions on heater duct and alternater fan housing. I did have to eliminate the airbox horn also.

Larger pusher fans above the condenser would move more air, however, some cutting of the tail louvers may be required and I did not want to do any cutting of sheet metal.

Mark,
Okay. I understand your situation.

If pusher fans are more efficient, is it possible to lower the mounting point of the condenser, then install pusher fans above? In other words, just swap the location of fans and condenser.

MHO, I don't think the add'l fans block significant air volume. The engine cooling fan is going to get air from whatever air source/opening and push it into the engine. IOW, no engine compartment vacuum is anticipated.

With the A/C OFF and aux. fan(s) ON, the engine should receive more ambient air at idle and low speed.

Sherwood

Sherwood, Pullers are more efficient than Pushers, but larger pushers could be mounted above the condenser (probably two 10" fans) that would move considerably more air. I thought about dropping the condenser down a little with some spacers, but I've got a rear wiper and the motor assembly would not allow.

I agree with you....condenser fans blocking of air through the grill not material (just my opinion).

Thanks!

Nice AC thread

Resurrecting this old thread to say thanks for all the info. Adding fans to my granite green ‘88 today. It can’t hurt!

Has anyone considered 2 10inch fans, one pushing and one pulling?