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Need electrical advice

Want to add 3 amp pump to existing forward condenser blower circuit. Point is for pump to come ON when blower does. Am inclined to splice a new + wire for pump into existing + wire feeding blower. Question: Will this make blower run slower?




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Old 06-27-2019, 03:41 AM
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As long as the fused circuit is capable of carrying the necessary amps, I don’t think it should be an issue.
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Old 06-27-2019, 03:55 AM
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Nice note on fuse Jack. TY. Will include 4 amp fuse in new + wire feeding pump. Believe existing fused circuit can handle 3 more amps but am sure fuse for that circuit is well above 3 amps for pump.
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Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver 930. '79 Black 930. '79 Anthracite 930.
Old 06-27-2019, 04:13 AM
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its the wiring size that is the issue.
fuse protect the WIRES and are sized for the wires.
if you take out a 5amp fuse and put in a 30amp then put a 10amp load on it, the wires will get hot, melt and then catch fire.

what I would do is look and see what all is on the circuit besides the fan blower.
then i would put an meter in place of the fuse and check the current with the blower on along with anything else on the circuit.

since i don't know wire sizes and current load for DC circuits i would look to see what size wires are used on circuits with about the same load to compare wires sizes.

another option is to mount a relay with the new pump and use the blower wires to engage the relay. then run the main power wires either directly to the battery, with a fuse, or run them back up to the fuse block and tie in on the TOP side of the block.

one other thing to consider is if you are pulling a low of current on the blower circuit the fuse itself can also heat up. they have very poor connections and cause resistance thus heat.

i would pull the wires out at the fuse block and clean the ends along with the fuse ends and the contacts for the fuse.

wiring for Porsche was an after thought, not their strong suit.
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Old 06-27-2019, 04:30 AM
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Add a relay on the blower side and run a separate fused 12V supply to the pump.
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Old 06-27-2019, 04:33 AM
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Was hoping to avoid relay and subsequent wiring that would require... That's reason am asking about splicing into existing feed.

Appreciate note on checking current but we're dealing with electroidiot here---I don't know why I'm doing that and then what to do with whatever current number is found.

Am going to dumb this down for my sake and propose: splice power feed for pump onto existing blower power feed... then run system with blower & pump ON while feeling wires. If wires warm up, shut system OFF and install relay as suggested. If after system runs for 5 minutes and wires do not get warm... splice approach is OK. Any objections to this?

(I cleaned all wire ends at fuse block and block connections a year ago.)
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Old 06-27-2019, 05:19 AM
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Agree that the relay's the best way to go (and isn't very difficult/involved to install) -- wiring to the front blower was sized to run the blower (only) adding an additional 3 amp (36 watt) load would be taxing the wires feeding the blower (and the rest of the devices on that circuit) beyond what they were designed to handle -- this thread has some good info on the ac circuits and current draw A/C Relay Question - front condenser fan inop (looks like the front condenser blower pulls 12-15 amps (depending on its condition) -- adding another 3 isn't insignificant.
Old 06-27-2019, 05:56 AM
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The car, motor, and wiring are old, and as implied by others, you may already be on the edge of stressing the circuit.
Your change is begging for a relay and at least one new in-line fuse. Finding out the existing condenser motor current draw would be a help to selecting the right size and confirming if your wiring after the relay is gonna be ok - we like some margin.

I think the load side is using a 25A fuse with a 4mm thk trunk wire, not sure what all else is on it.
The wire steps down to 1.5mm or ~16AWG that will handle 10A on that leg.
So, 10A minus the pump 3A leaves 7A for the existing condensor. These are WAGs.
As far as hand testing, you might feel the heat, but you won't be able to get your hand to every spot on the harness.

Edit:
Just saw darrins post, yeah that's warm
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Old 06-27-2019, 06:21 AM
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Consensus: run pump from an added relay. OK. Will include inline fuse between power & pump.

Thanks to each of you for input on this...
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Old 06-27-2019, 06:45 AM
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A/C fuses.



^^^^^
Fuses.

Best,

Gerry

]



^^^^^
The blower fuse will prevent this.

Also, I reduced the current load on fuse #2 by re-routing the condenser fan to fuse #3.
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Last edited by 86 911 Targa; 06-27-2019 at 07:25 AM..
Old 06-27-2019, 07:23 AM
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Fuse re-routing.




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Old 06-27-2019, 07:28 AM
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go find a pretty girl to feel, your not getting ANYTHING out of feeling the wires.
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Old 06-27-2019, 08:48 AM
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Have heard of front condenser blower motors burning up... and so good reason to independently fuse that circuit. Have never seen toasted outcome until now---thanks for driving point home Gerry. Illustrated guidance is impressive---much appreciated. Am not getting how rerouting condenser blower to #3 lowers load?

T7... Pretty girl's in bag. Wire feeling only done very rarely.
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Current: '80 Silver Targa w /'85 3.2
Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver 930. '79 Black 930. '79 Anthracite 930.
Old 06-27-2019, 09:57 AM
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If you’re an electrical newbie, good luck following the factory wiring diagram. Better to locate a diagram that describes only the blower circuit, then study that. Suggest you don’t install this by a paint-by-numbers approach. You might let out the smoke. Fortunately, all standard one make-one break relays have pretty standard connections.

Suggest controlling both fan motor and pump with a single 25-40 amp relay. Branch the circuit at the relay so each load has their own current path. For a more conservative approach, use two separate relay circuits controlled by the blower switch.

Sherwood
Old 06-27-2019, 10:58 AM
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oh BTW, my front fan caught fire when the PO had my car. just something to consider since it was brought up
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Old 06-28-2019, 04:49 AM
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Just guessing, you want to spray water on the condenser coil to enhance the cooling effect???

BUT, The concern with parallel motors starting at the same time is the current surge for both motors.
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Old 06-28-2019, 08:48 AM
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Toggle switch under dash.
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Old 06-28-2019, 09:33 AM
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Quote:
Originally Posted by 3rd_gear_Ted View Post
Just guessing, you want to spray water on the condenser coil to enhance the cooling effect???

BUT, The concern with parallel motors starting at the same time is the current surge for both motors.
Quote:
Originally Posted by Joe Bob View Post
Toggle switch under dash.
If you are wanting to just spray water on the condenser to aid in the cooling Joe Bob is right, just use a switch that is separate. Maybe get fancy and add a 5 second timed switch so you get 5 seconds of water. You don't want to saturate it too much and use up the ware source.

Of course the best thing for AC improvement is add condensers to the rear fender, but that is a different can of worms.
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Old 06-28-2019, 10:01 AM
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