Adding 3 cooling fans to rear A/C condenser
 

Working on my wiring plan for a three 7.5" Spal pull fan add to the underside of my rear A/C condenser. Three 7.5" fans will cover the entire surface area & will fit in this tight space. Will be adding relays wired directly to the + on the comperssor to turn the fans on/off. Planning on running a new hot lead direct from the battery to power the fans with inline fuses. Each fan is rated at 7.5amps and pull 440 CFM.

Need suggestions for getting power to the fans.

Best route to run a positive lead from the battery to the engine compartment?

If I run a cable into/through the cabin, can I get to the engine compartment through the tunnel opening on the floor between the rear seats?

Thanks!

Anyone have any experience running a new Pos lead from the battery to the engine compartment?

Thanks!

I did a similar project on my '89 and used one of the empty slots in the fuse box in the engine compartment....no need to run a dedicated wire all the way to the battery itself.

Great idea. I've got three open fuse slots, but didn't know if it would be OK to use. Glad I asked. Problem solved.

Thanks!

Are you running barrier hoses? Have you thought about a pro-cooler (front ac condensor) to lower your vent temps?

My 69 has fans on the rear condensor too.

How are you going to fit the fans? Do you have a turbo tail?

Have you considered switching the fans off of the same wire that switches the compressor?

You do realize that there's a huge fan sucking air through the condenser, right. The only time the three fans are likely to help is when you are at idle.

I'd love to see some empirical data on whether fans on the rear condenser actually help. Some on this BBS swear that they help. I'm skeptical.

I agree if anything, the one in the middle would probably be a waste even at idle.

No barrier hoses, although I replaced two of the three hoses this summer along with the rear condenser, drier, ft condenser motor and evaporater motor. $1,900 later I got my vent temps down to the mid 30's to low 40's. I'm convinced that the greater the airflow created through the undersized and poorly placed condensers, the better.

And, yea I've got tail! ....with the notched condenser for the rear wiper. :)

IMHO, your time and money would be better spent putting a condenser and fan in the front left fender.

If you've got a tail then you are getting even more air at speed than a car with no tail. So you are getting temps in the 30s and that's not enough. I'm guessing that you need another condenser.

I'm thinking my stock A/C system that is now fully operational will be OK. But with a little tweeking (i.e. relatively low cost fan add) I can improve its efficiency. In stop and go traffic my vent temps go from the mid 30's to the low-mid 40's at a standstill then back down when I get moving and get air flow back up. I'm hoping the fans will lower the high end of my vent temp range. Make sense?

Sure, like I said, the only time the fans will help is when in stop and go. Is the fan for your front condenser working?

Steve, this car is my daily driver. Call me a little obsessed but very unpleasant memories from this summer linger (trying to get my system working). I'm sure you can relate. The only city I've lived in hotter and more humid than Atlanta or Tampa is Houston.

Yep, front condenser motor and evap motor were both fried and were replaced.

Funny, I've lived in Tampa too, so yes, I understand about heat. At least you have an '87 so you have the updated vents. Something needs to be done to the center vents to allow them to both point at the driver, and the far left vent should be closed. I'd guess that the fans should definitely help in stop and go. Good luck.

Install a trinary pressure switch in the discharge line of the compressor. In addition to having high and low pressure cutouts (opening contacts) it has an extra set of contacts that close at intermediate pressures (such as when the deck lid condenser loses effectiveness due to lack of air flow). This extra set of contacts can be used to energize either the fans directly or through a relay.

Vent air temperatures below 35F are not really very useful as they indicate the evaporator is at or below 32F and it will ice up and block air flow. If you're at 40F or below and need more "cooling", work on improving the air flow through the evaporator, dash and around the interior of the car.

What's your source on the fans?

Jack, my fan source is The Fan Man......$53 each for 7.5" spals. Best pricing I found.

http://www.the-fan-man.com/shop/size-pull-part-0358-p-179.html?cPath=33

Thanks!

only one
 

I only have one elec fan added under my rear condenser and I believe it helps. But the three fans your talking about will be a very tight fit.

I live in the ATL and get low-mid 30 after improving the air flow from the evap box. There's much to be improved there.

Jim thanks for the suggestions. What's your opinion on mounting a small fan at the evaporater intake opening behind the passenger floorboard. I recall seeing a post where a guy mounted a computer muffin fan. This fan would be totally ineffective IMO but I like the idea. Spal makes a 4" Motorcycle/ATV fan that moves 124 CFM. I don't know the CFM rating of the evaporator fan. I'm no engineer but I would seem to me that "assist" fan at the intake might improve the efficiency of the evap fan. I also recently ran across an evap fan upgrade with a HD fan boasting a 50% improvement in CFM from the OEM fan (got me thinking)

Derk, what did you do to improve your evap airflow? I haven't looked but wouldn't be surprised if my evap box is a dirty mess.

"I recall seeing a post where a guy mounted a computer muffin fan."

That would be me; the computer "muffin" fan will make an airflow through the evaporator and ducting even without the main blower running so it does move air. The more delta P there is, the more air is moved. Plus it is pushing air directly into the evaporator core. A further advantage of that computer fan is that it draws a "whopping .45 of a watt" and is quiet. A bigger, high output fan in the passenger foot well likely will make increased noise which may grow tiresome. If it has never been done since the car was made, removing the evaporator core and cleaning it can be helpful as can fitting seals between the evaporator core and the housing to reduce air bypassing the core. Also consider installing a modern evaporator and a higher output fan. Note that higher output fans may be noisier than stock if the higher output is achieved by running them at higher rotational speeds. Cheers, Jim

Modern evaporator core and expansion valve fitted into OEM (factory A/C) evaporator/blower housing. Note the additional foam sealing on the sides to reduce the bypassing of inducted air.http://forums.pelicanparts.com/uploa...1162520634.jpg

Jim, small world. I hope my comment about the muffin fan didn't offend you....my only point was that I did not think they move much air. You're spot on with the noise issue....my concern also with a larger fan.

What's involved in cleaning out the evap box. Does it require disconnecting and recharging the system? I had to do that twice alreay this summer in my repair fiasco....fix one leak and create another, etcetera, etcetera! Can I clean and re-seal without disconnecting any hoses?

I'm not offended; I too was surprised how much air flow the "muffin" fan produced.

"Can I clean and re-seal without disconnecting any hoses?"

Not too likely, unless for some reason there is a lot of slack in the refrigerant hoses going to and from your evaporator.

Jim: I know that several vendors have the modern evaporators and expansion valves, but where does one get a higher output fan that will fit?

Thanks.

ScottB, I found the link that I ran across the other day for the high output evap fan that fits the stock evap box. Has anyone tried one of these?

http://www.mrjaguar.com/porsche/porsche911carreraac.html

Scroll down to:

"Replace that "wimpy" OE Blower Motor with a more powerful 3 speed motor that allows you to lose the Resistor A/C intake restriction and add more Blower speed control. Will give you up to 50% more CFM as compared to OE!"

I did this with muffin fans on my ROW 84 Targa. I still get crap for air flow from the vents, but its better. My A/C and vent plumbing is very different from the US cars I've seen. For example, I get A/C out of the windshield, dash and under dash vents, which is nice for defogging, and I don't have the bowtie thingie. Its some kind of aftermarket system for a car that originally came without A/C. But in 95-100 degree LA summer days, I get mid 30s on the dash vent temps, just not a lot of CFM, and thats with R-134a and a Jim Sims subcooler.http://forums.pelicanparts.com/uploa...1162530399.jpg

Here's one of my favorites,
evap box

I've also replace the evap fan with one from Grainger, but haven't written anything up on this yet.
I believe the air flow has improved.

I followed Jim's idea here. I was happy with my A/C before, but this improved it some more.

Brian

I like the idea of moving air in the cabin to the evaporator inlet. Unfortunately, I think our cars suffer from 'short cycling'. The cool air is sucked right back into the system. A better solution would be an air return that uses the center tunnel and draws are from the rear of the cabin via ducts under the seats.

For the factory A/C cars which have an evaporator/blower housing which inducts air from both the passenger foot well area and the tunnel this could be accomplished by louvering the cover plate over the shift coupler and mounting a muffin type booster fan within the nozzle that leads from the tunnel to the evaporator/blower housing. I seem to recall that there were some shift coupler cover plates that came from the factory louvered but these may have been for the cars equipped with the front gasoline fueled auxiliary heater.

My '68 912 had the louvered transmission connection cover. PET's picture for 65-69 911-912 shows louvered. It must have been some time later when the solid covers started showing up. I swapped my solid one for a louvered one when I installed A/C in my '80 Euro SC, and I had to make a cutout in the solid carpet that covered the plate.

I recommend fans and posted on this some time ago

http://forums.pelicanparts.com/porsche-911-technical-forum/302888-ac.html

OK, here is a picture of the fans laid out on a cardboard template of the rear condenser. Three 7.5" fans appear to maximize the surface area of the condenser without any overhang as there is no room for any overhang. Waiting for three sets mounting feet to arrive before getting started. Will attach to underside of condenser using nylon push through fastners.

http://forums.pelicanparts.com/uploa...1162950102.jpg

http://forums.pelicanparts.com/uploa...1162950170.jpg

Thanks all for your comments and ideas!

"using nylon push through fasteners"

This mounting method has caused problems (tearing through the fins and channel leaks) when used to mount electric fans to vertical radiators. The deck lid condenser may be robust enough and your fans small enough that it may be okay in this case.

Checked with my source on that very issue (The Fan Man) and he stated that push throughs are not recommended for radiators but should be OK for this application. Sounds like you are in agreement Jim ?

Don't have any data on the Porsche condenser use but they are thicker than many modern radiators, some of which seem to only be 10 mm thick. I guess you (or rather your car) gets to be the "guinea pig." Did the "Fan Man" know your condenser is tilted and not vertical?