Learn me: A/C fan switch / electrical
 

I have no idea the last time the A/C was run in my car. When I bought it, there was either a blown fuse or no fuse in the circuit that controls the dash vent fan (can't remember.) The front condenser looks like it's been monkeyed with a bit too.

I decided to throw a charge in the system and see what happens. Well, it works. I have pretty cool air coming out of the vents. The decklid and front condensers both get quite warm. The front condenser fan next to the battery works, but is noisy.

The fan works at all speeds, but the switch base feels like it gets quite warm - warm enough that I have concern. Also that front motor makes me a little nervous. Is there anything I should consider re-wiring, replacing, or improving in the circuit? Is the warm fan switch normal? Is there a modern alternative to the front condenser fan or do I have to replace with OEM?

Driven97,
The front condenser fan needs an inline fuse to prevent melting down the wiring harness if the motor fails.

http://forums.pelicanparts.com/uploa...1374584363.jpg

http://forums.pelicanparts.com/porsche-911-technical-forum/427532-cfm-front-ac-condenser-fan-3.html#post6972064 When I checked mine, the brush holder had started to melt down.

A footwell blower motor can be used for the front condenser fan motor, I think BarryJB found this - it spins faster than the stock motor, and is the same dimensions as the original motor. http://forums.pelicanparts.com/porsche-911-technical-forum/427532-cfm-front-ac-condenser-fan-2.html#post6961577

Mike

Try cleaning all the contacts at the switch. Dirty contacts cause resistance increase and this in turn results in heat at the contact. It could also be that the internals of the switch are corroded from not being used, in this case you need to replace the switch.

+1 on adding the in-line fuse as mentioned above.

Fuse to the front condensor's blower is a great idea. Below... blower motor brushes without a fuse. The variable switches... I've found they just rot out over time.

http://forums.pelicanparts.com/uploa...1374586225.jpg

http://forums.pelicanparts.com/uploa...1374586416.jpg

OP would be better off on more counts than one to add a relay to pick up and power the motor directly from a fuse to the battery. No heating of the switch contacts and more STABLE battery power to the motor.

Or even better yet...

http://forums.pelicanparts.com/uploa...1374590553.jpg

What is it WW?

12 volt 30 amp PWM DC motor controller, $20 on ebay.

Or:

http://www.aliexpress.com/item/Free-shipping-5pcs-9v-28V-30A-DC-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V/640044963.html

Ok - thanks for the replies.

I'll at least fuse the front fan, and probably swap to a relay control. In the photo is a 7.5A, but the linked thread says 10A gives more headroom for startup - so 10A?

For the switch - let me know if I have this right: The OEM uses power resistors, which dissipates power as heat to slow the fan. A PWM control turns the fan on and off at a high frequency, with a variable "on" time?

EDIT: How much current for the blower motor?

Yes. PWM, Pulse Width Modulation, varies the 12 volt "on" time, generally 90% power use efficiency throughout the speed range.

Reading comprehension fail. Sometimes I wonder how I get by. Thanks for the help.

Ty ww ~

Front condenser fan fuse holder.
 

Here's the Porsche part.

It's plug & play......

http://forums.pelicanparts.com/uploa...1374608763.jpg

http://forums.pelicanparts.com/uploa...1374608790.jpg

http://forums.pelicanparts.com/uploa...1374608817.jpg


Good luck,

Gerry

Driven97,
I started off with a 7.5 amp fuse based on the running current of the motor. The starting current blew the fuse, so I ended up using a 10 amp fuse. This is for a footwell blower motor.

86 911 Targa - Thanks for the fused harness part number.

Mike

10A is the correct value for the footwell blowers.

I ran dedicated line from the battery yesterday, going through a relay, through a 10A fuse. Possibly overkill. My fan housing was also a bit buggered - leaves in there, housing cracked, missing clips, motor loose, squirrel cage scraping on housing, and taped together in places.

I also ordered one of those PWM controllers, I get to figure out how to wire that as soon as it comes in from China.

My one of these showed up from China yesterday. The SOB works by modulating the ground on a common positive. That would be awesome if the car was positive earth, which it is not.

So, to use it, I either have to run dedicated lines from the PWM to the blower or swap polarity on the motor end and run a fused constant hot to the A/C blower right from the battery. Neither of those sounds like fun, and one sounds like a bad idea. Maybe I'll just buy a new OEM switch.

Like many have said... Ignore recommendations from wwest... You just will pay twice

If it were me I'd buy the Kuehl switch so you have variable air. It's plug and play...

Yup, going through some other threads looks like he has been banned. Ah well.

For posterity - if anyone else finds this thread in the future, do not buy the PWM pictured. I'll probably try and make it work since I like a challenge, but it's probably not worth it. Worst case I'll have a neat little $18 PWM I can try and invent a use for.

We tried one, it lasted less than 12 hours running continuously at 3/4 load.
If you buy a box full of them, you should be OK.

http://www.cademo.com/arcade/images/...sw_marquee.jpg

Fuuuu. Guess I'll just buy an OEM switch. Looks like the part has been updated.

Griff's variable fan speed controller has been working well for me for the last five years.

Griffiths supplies a range of air conditioning components for your Porsche 911,911s,911t,911 turbo, and 930, such as: Porsche air conditioning upgrades, Porsche air conditioning improvements and updates: Porsche barrier hoses and hose sets, Porsche c

It costs much more than $20. It is plug and play. It works, and works, and works, and works, and works, and works, and works...well, you get the picture.

https://lh5.googleusercontent.com/-S...o/IMAG0111.jpg

FWIW, it's in with a reasonable amount of fuss.

A PO had a large blue switch between the knobs that didn't do anything, but judging by a wire tap back there at one point it was to switch the AC circuit off and on. Seemed like a good idea, so I got a fresh switch and did the same. Now I can run the dash vents without AC at all if I choose. If the PWM holds up, I'll adapt the OE knob so that it'll look close to factory.

I ran it for about an hour yesterday, the PWM barely got warm. I have high hopes. Also of note: My fan at full blast was drawing only about 10A, the AC circuit alone was drawing about 4A.

Not bad for $25.

I'm confused - my front condenser fan run at about 3.7A, no-where near the 7.5A or 10A talked about here and other threads. Mine works, it runs happily without getting anything hot, but I imagine it's not very effective as a condenser! Any thoughts??

I didn't check the run current for mine, but I'm going to go out on a limb and guess that the inrush current is much higher than the run current. A brushed motor at startup is basically shorted with only winding resistance until it starts turning.

tl;dr Basically it might reach 7A for the first split second then level off to 3.7A.

Yes, that's what I'm guessing, but the low run current was what surprised me.
I'm hoping for confirmation of the expected run current, and comparison with other blower motors run current, to see if it is worth replacing it.
Thanks.

I think the running current of the blower motor on mine was less than 5 amps, but I agree with Driven97 - the current of a starting motor can be 2 to 3 times the running current. I also used foam to seal around the front condenser to body, which would put more load on the motor.

Mike

Front condenser blower motor current.
 

http://forums.pelicanparts.com/uploa...1376095216.jpg
^^^^^
As measured on our '86.