Aux AC Fans

[wieringa@mcn.ne]

As a test I am wiring in an extra fan above my rear ac condenser to see if it helps. Probably going to run it off a relay triggered by the ac clutch. Just wondering where the best place is to tap 12 volt power near the engine that will not cause issues. I need 5 amps / 10 if I use two fans.

Thanks

KW

[kuehl]

CFM of 'aux' fan vs. CFM of engine fan?

[wieringa@mcn.ne]

Sorry I left out some detail. 1550 cfm from the fan and unsure of the engine fan. 82 911 SC stock. Saw a thread that mentioned adding fans above the rear condenser to help with the issues of early 911 AC. My rear tail has room to put up to two 9" fans abover the rear condenser. Yeah I know - 911 with old York R12 system but it does blow cool air and I am not ready for the big $ upgrade it takes to really fix the problem. Installed one fan today and just powered it off the AC clutch circut and no blown fuses yet. I will see if it helps and maybe add a second fan and go for a relay setup. Just didn't know a good place to tap power close to the engine that was reasonable to ge to.

KW

[khamul02]

It would be interesting to know the exact temp difference if any occurs with that fan on and off?

[kuehl]

Well lets see if this will help a bit:

Electrical:
Assuming a typical high quality 9" pancake motor fan (51mm thickness) curved blade, pushing, may give you 625 cfm at 0 static pressure. At 13vdc the amp draw will be about 7.2 amps running and probably 11 amps on start up (about 2 to 3 seconds): all values are nominal. Multiply by 2 and you have a 14.4 constant nominal draw. The compressor side of the A/C circuit, runs through the thermostat switch, which I recall from a discussion with the OEM, only supports 5 amps (conservative). A common A/C compressor clutch coil draws 4 amps nominal (and in many cases when you check the voltage back there its well under 12vdc due to resistance in the long run). So from the start you know with 1 fan you already are suffering from the Health Care Tax and with 2 fans you are headed to the guillotine;
as a note we have run a single fan through the circuit.

So your next point of spreading out the amp-tax is tap off the engine bay power panel, you can use the top fuse contacts: install a common 30 amp A/C relay and make a "Y" connector at the compressor power wire near the oil filter to trigger the relay.

Mechanical
I'm not intentionally raining on your parade project. Fans under and over the deck lid condenser have been in use for years. But, personally (IMO is the cliche), if I felt fans over the engine deck lid condenser were the perfect cure to constant lower vent temps I would have bought a factory building in Newark 15 years ago, revitalized the lost art of mold building in NJ, resurrected the pioneer plot of Dr. Weston's talents, and corned the market with one giant flood.
Yes, pushing/pulling more air through the deck lid condenser does lower system pressures, which correlates to lower vent temperatures ... logically but not always. The fact is the engine's cooling fan pulls in more air than any electrical fan(s) you can easily design into the footprint. How much more is a variable based on engine rpm, and I'd say it conflicts starting near 2000 rpms (I'm sure there are a few threads buried here or in the Renn that shed some light).

So, in the nutshell, you may see a lower vent temp at idle, however once the engine's cooling fan's cfm exceeds the Aux fans something is going to be in the way so to speak, such as the footprint area of the fans above the engine fan.... they will be in the way and shadowing the area below or above the condenser and impeding air flow through the adjacent cooling fins.

Another Avenue of Attack
Its very understandable in today's economic climate that we may have to hold-off on a full overall of the A/C system (compressor, hoses, evap, fender condensers, etc.). But, there is one part of the formula to comfort that is sometimes overlooked and is very economical, that is 'ventilation'. The early 911/930 (prior to 1986) does not have enough vent volume; you have the primary a/c vent above the radio, 2 small slotted vents left and right, and the famous 'bow tie' vent in the bulkhead (in front of the center console). If you were thinking of low vent temperatures as being the key to comfort then you missing out on the other half of the equation "air volume". For instance, my 2005 Touareg, with its PF condenser (which is falling a part) never produces vent temps down in the 30's. It is properly charged however is lucky to get down in the low 40's. The monster does take a bit of time to cool down after getting heat soaked in the sun all day, but during the process I do feel comfortable simply because it has plenty of vents and an enormous amount of air blowing out of them; and the automated climate control smartly cranks up the volume or cfm's full throttle in the beginning of the phase ... tons of air blowing through that is frankly more near 50-60 F in the initial cooling phase. And it feels great. A bit noisy, but simply great. The mass of air blowing into and over you simply cools you down do to the process of 'evaporation' of the moisture on your skin.
Much alike opening the window of your car, sticking your head outside and driving fast.

So, the alternative approach to obtaining comfort is simply to add more vents to your car and increase the volume of air output out of all of the vents with a higher output evaporator fan motor. A bit more in cost than 2 fans over the engine condenser however a more logical solution in the progress of steps to doing the job right, once, the first time.

[wwest]

Mechanical

I rather doubt that the problem most are experiencing with poor A/C capacity is during consistently higher speed driving wherein the engine fan is likely to be sufficient. So the electrical fan solution becomes most viable in city slow or stop and go driving.

"...fans will be in the way.."

In theory, yes, but first the current flow to the electrical fans will decline as the air volume produced by the engine fans rises. Yes, at some point the new fans will become generators, slightly impeding the flow. But I suspect that might be in the range of 4000RPM and above and therefore of no real matter.

Another Avenue of Attack

You, of all people, should know better than to suggest this as an initial viable solution.

Additional airflow will help ONLY if the overall system, otherwise, is already producing enough cooling capacity, BTU's, to keep the evaporator vane surface area below ~34F. If the evaporator vanes surface temperature rises with fan speed then the shortcoming is elsewhere.

I think you might agree that be the case, primary shortcoming, with the factory A/C.

There are really TWO issues with the factory Porsche A/C...

1. Cabin cooldown RATE. How fast can the system bring the cabin atmosphere, and to some extend cabin surfaces, down to the desired comfort level.

2. Once the cabin is cooled satisfactorily, atmosphere, etc, how adequate is the system at keeping it that way?

My personal preference at "2" is to lower the blower speed as much as possible, while still maintaining the comfort level, and direct the outlet airflow elsewhere other than directly into my face and upper body.

[wwest]

Originally Posted by wieringa@mcn.ne

Sorry I left out some detail. 1550 cfm from the fan and unsure of the engine fan. 82 911 SC stock. Saw a thread that mentioned adding fans above the rear condenser to help with the issues of early 911 AC. My rear tail has room to put up to two 9" fans abover the rear condenser. Yeah I know - 911 with old York R12 system but it does blow cool air and I am not ready for the big $ upgrade it takes to really fix the problem. Installed one fan today and just powered it off the AC clutch circut and no blown fuses yet. I will see if it helps and maybe add a second fan and go for a relay setup. Just didn't know a good place to tap power close to the engine that was reasonable to ge to.

KW

Just be sure an locate your 2 fans nearest the compressor inlet to the condensor.

And be sure and check that the thermostatic switch, at full tilt, still opens before the evaporator begins to freeze up.

[kuehl]

Gee West, I never expected you to respond to my post!

[Brorag]

I was initially swamped by all the contradictory input that sometime seemed to be self serving. On the other hand, some of the input (Kuehl) is studied and well considered.
All of this stuff is a matter of degree. How much you want to throw at your 911 to get it cool?

For some of us living in temperate or cold climates it's not that big a deal. For those of us living in places where temps can often exceed 3 digits with accompanying high humidity, AC can significantly extend the amount of time you can use your car.

All I know is, I did what I described (complete with a couple of documented dead ends) and it worked for me. My $.02 is don't get too lost in the rethoric.

Remember the basics:

• the 911 is designed to be slick.
• porsche did not design ac into the 911 shape.
• the 911 shape is designed slick to go fast.
• ergo, ac stuff is tucked into a slick 911.
• air traveling across hot ac juice finds its path more difficult than traveling across slick--air will travel the least hardest way, i.e., the slick way.
• it's also important that you have a tight cabin so the AC isn't working a handicap by trying to compensate for hot air leaking in through cracks or open ports.
• Those of us with cabs pay an extra penalty because cabs seem inherently leaky.
• To its credit, my system is cooling the cabin is spite of it being a ragtop.

Once the plumbing is tight, blowing more air in the right places can help

• best way to blow air--fans
• the best place to start is to focus air is where the ac juice is must exposed.
• that is the condenser, a.k.a. radiator stuck under the engine lid.
• I added fans. (see above) It was the most significant help, and most cost effective.

Remember that you need a tightly plumbed and pumping ac juice system:

• you are sucking heat out of the cabin via ac juice through the goesinta (evaporators, a.k.a. radiators) that run cold ac juice past cabin air, sucking the cabin heat into the ac juice
• you are trying to get that heat out of the ac juice after it absorbes cabin heat;
• it's done via goesouttas (condensers, a.k.a. radiators) that run hot ac juice past outside air
• ac effectiveness (deg of cold/dry in cabin) is dependant upon how much air comes into contact with the hot and cold juice, & outside temp.
• a well plumbed, unleaky juice circuit is essential
• I did not have a tightly plumbed and pumping ac juice system, and had to replace that too: hose, pumps, condensers, evaps, juice filters--the works.
• Ordered the system and installed myself, then took it to the local shop for vacuuming and charging with AC juice.
• It's been operating for 3 summers and is working well.

I first tried to get the old system to work (it was designed to leak!)

• new pump
• lots of vaccums and replacement freon--then freon price went up
• converted system to new freon--system still leaked--not reliable
• little or no cold air

I also replaced the front fan. I looked at the original design and concluded that is was inadequate because:

• it had seized (no bearings, used bushings) and was not fused
• it was cheaply made, which contributed to above.
• it was prone to overheating and catching fire if it melted in a way such that it directed lots of amps to ground.

It's replacement was a better designed/built industrial rated fan motor that doesn't run as fast or hot.

• I also included an in-line fuse.
• you might consider an original replacement, but ck it often and make sure it's fused
• The front fan helps, but it's not as effective as addressing the condenser under the engine lid, because you can blow lots more air across a much larger surface.
• My opinion is to first get more air across the large condenser under the engine lid via fans. (first disconnect or fuse front fan because of above)

So, if all this ac hooha just causes you a headache, and you have lots of $$, take your chances, pay up, and enjoy the results. To a greater or lessor degree, you will probably need to do at least some improvements for some permanent correction.

You do have some control here by sorting out what order of improvements bring you the best return for your particular ride. To do that, you gotta know the basics.
Just my $.02.
JD

[wwest]

1. I have NOTHING to sell.


2. Free advice is often worth what you pay for it.

[wieringa@mcn.ne]

Wow yeah what he said. Makes sense that at some point the engine fan cfm will overcome the electrics and the will then somewhat limit flow. The total lack of vent flow rings very true. Many days I wish I just had just a good fresh air vent. I do have center vent somwhere in my shop to replace the "bowtie" that I need to install. Already installed one 9" fan so I'll report on it's slow speed around town results. In the end I am sure I will find the best way to lower temps is to get Kuehl.

KW

[Joeaksa]

Originally Posted by kuehl

Gee West, I never expected you to respond to my post!

Good laugh this morning. He sure does like your posts!

[Joeaksa]

Originally Posted by wieringa@mcn.ne

Wow yeah what he said. Makes sense that at some point the engine fan cfm will overcome the electrics and the will then somewhat limit flow. The total lack of vent flow rings very true. Many days I wish I just had just a good fresh air vent. I do have center vent somwhere in my shop to replace the "bowtie" that I need to install. Already installed one 9" fan so I'll report on it's slow speed around town results. In the end I am sure I will find the best way to lower temps is to get Kuehl.

KW

KW,

The big question is, are you stuck in traffic or at a light fairly often? If yes then personally I would put at least one fan on the rear condensor to guarantee that there is airflow over the fins. If you rarely get stuck in traffic then might try the system without the fan.

I just did my system and put a single 7" fan on the rear condensor, triggered just as you mentioned with a relay off of the A/C clutch trigger wire. I rarely get stuck for longer than 2-3 minutes in traffic or at a light but it does happen.

[wwest]

Trinary high pressure side sensing switches are available that have a separate switch set to control the rear lid cooling fan(s) as long as the high side pressure is above a specific level. Might be a good idea to use one of those to run the new fans.

[wwest]

Originally Posted by kuehl

Well lets see if this will help a bit:

Electrical:
Assuming a typical high quality 9" pancake motor fan (51mm thickness) curved blade, pushing, may give you 625 cfm at 0 static pressure. At 13vdc the amp draw will be about 7.2 amps running and probably 11 amps on start up (about 2 to 3 seconds): all values are nominal. Multiply by 2 and you have a 14.4 constant nominal draw. The compressor side of the A/C circuit, runs through the thermostat switch, which I recall from a discussion with the OEM, only supports 5 amps (conservative). A common A/C compressor clutch coil draws 4 amps nominal (and in many cases when you check the voltage back there its well under 12vdc due to resistance in the long run). So from the start you know with 1 fan you already are suffering from the Health Care Tax and with 2 fans you are headed to the guillotine;
as a note we have run a single fan through the circuit.

So your next point of spreading out the amp-tax is tap off the engine bay power panel, you can use the top fuse contacts: install a common 30 amp A/C relay and make a "Y" connector at the compressor power wire near the oil filter to trigger the relay.

Mechanical
I'm not intentionally raining on your parade project. Fans under and over the deck lid condenser have been in use for years. But, personally (IMO is the cliche), if I felt fans over the engine deck lid condenser were the perfect cure to constant lower vent temps I would have bought a factory building in Newark 15 years ago, revitalized the lost art of mold building in NJ, resurrected the pioneer plot of Dr. Weston's talents, and corned the market with one giant flood.
Yes, pushing/pulling more air through the deck lid condenser does lower system pressures, which correlates to lower vent temperatures ... logically but not always. The fact is the engine's cooling fan pulls in more air than any electrical fan(s) you can easily design into the footprint. How much more is a variable based on engine rpm, and I'd say it conflicts starting near 2000 rpms (I'm sure there are a few threads buried here or in the Renn that shed some light).

So, in the nutshell, you may see a lower vent temp at idle, however once the engine's cooling fan's cfm exceeds the Aux fans something is going to be in the way so to speak, such as the footprint area of the fans above the engine fan.... they will be in the way and shadowing the area below or above the condenser and impeding air flow through the adjacent cooling fins.

Another Avenue of Attack
Its very understandable in today's economic climate that we may have to hold-off on a full overall of the A/C system (compressor, hoses, evap, fender condensers, etc.). But, there is one part of the formula to comfort that is sometimes overlooked and is very economical, that is 'ventilation'. The early 911/930 (prior to 1986) does not have enough vent volume; you have the primary a/c vent above the radio, 2 small slotted vents left and right, and the famous 'bow tie' vent in the bulkhead (in front of the center console). If you were thinking of low vent temperatures as being the key to comfort then you missing out on the other half of the equation "air volume".

For instance, my 2005 Touareg, with its PF condenser (which is falling a part) never produces vent temps down in the 30's. It is properly charged however is lucky to get down in the low 40's.

The monster does take a bit of time to cool down after getting heat soaked in the sun all day, but during the process I do feel comfortable

simply because it has plenty of vents and an enormous amount of air blowing out of them; and the automated climate control smartly cranks up the volume or cfm's full throttle in the beginning of the phase ... tons of air blowing through that is frankly more near 50-60 F in the initial cooling phase. And it feels great. A bit noisy, but simply great. The mass of air blowing into and over you simply cools you down do to the process of 'evaporation' of the moisture on your skin.
Much alike opening the window of your car, sticking your head outside and driving fast.

So, the alternative approach to obtaining comfort is simply to add more vents to your car and increase the volume of air output out of all of the vents with a higher output evaporator fan motor. A bit more in cost than 2 fans over the engine condenser however a more logical solution in the progress of steps to doing the job right, once, the first time.

"..during the process.."

Wow, you truly are out of touch with reality, at least with regard to modern day (Touareg) automotive A/C designs anyway.

Your Touareg most likely has a SURPLUS of cooling capacity but the system designers have chosen the path of lowering passenger discomfort via using the reheat/remix method to moderate, modulate, the level of cooling AUTOMATICALLY supplied. If you want quick, quickest cooldown on a hot day with the interior fully heat soaked:

1.) Lower the (rear) windows slightly.

2.) Change the system to FRESH mode. Most will go automatically into recirculate mode (Denso US idiocy) in this situation.

3.) Move the setpoint to maximum cooling.

4.) Should the A/C blower not go into maximum flow mode then manually do so.

5.) once you "feel" that the cabin atmosphere (vs the HOT interior surfaces) has declined to or below the OAT then switch the system to recirculate.

6.) Once the atmosphere and the surrounding radiant effects have reached your comfort level then return the setpoint to your desired comfort level and to fuly automatic mode.

If you happen to be driving one of the new water cooled Porsches then be sure and manually close the windsheild outflow path. Otherwise you will not only lose a lot of cooling capacity through the windshield glass but might find yourself with a slowly fogging over exterior windshield surface just as "day" transitions in dusk.

"..I do feel comfortable.."

Modern day A/C systems are designed to minimize driver and passenger discomfort, no MASS of COLD and DRY airflow to chill body surfaces.