Learn me: A/C fan switch / electrical

[Driven97]

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?

[MConn]

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



cfm on the front AC condenser fan 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. cfm on the front AC condenser fan

Mike

[scarceller]

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.

[Discseven]

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.

[wwest]

Originally Posted by Discseven

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.

I suspect, quite strongly, that having a fuse in that circuit would have made NO DIFFERENCE..!!

Your brushes had worn down to the point of fairly high resistance with the rotor commutater, even just a few hundred milliohms maybe. The current flow would have been reduced accordingly but the local HEATING due to that "slight" resistance was what melted the brush holders.

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.

[wwest]

Or even better yet...

[Discseven]

Originally Posted by wwest

Or even better yet...

What is it WW?

[wwest]

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

[Driven97]

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?

[wwest]

Originally Posted by Driven97

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.

[Driven97]

Originally Posted by wwest

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

Originally Posted by Driven97

EDIT: How much current for the blower motor?

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

[Discseven]

Ty ww ~

[86 911 Targa]

Originally Posted by Driven97

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?

Here's the Porsche part.

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








Good luck,

Gerry

[MConn]

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

[86 911 Targa]

Originally Posted by MConn

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.

[Driven97]

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.

[Driven97]

Originally Posted by wwest

Or even better yet...

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.

[brads911sc]

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...

Quote de wwest

Or even better yet...

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.

[Driven97]

Originally Posted by brads911sc

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.

[kuehl]

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.