I'm stupid, whay doesn't this work?

[mrltd]

Got a 2 speed fan. 3 relays.

I wired it so that an adjustable thermostat gets acc power and triggers a relay for the low speed fan. The second relay is connected to the AC compressor. The third relay is wired normally closed in between the thermostat and the low speed relay. It is connected to the AC relay so it should open the 3rd relay and not have both fans running at the same time...it doesn't work.

[85crownHPP]

It is connected to the AC relay so it should open the 3rd relay and not have both fans running at the same time...

ther are a lot of ways to be 'connected to' a relay - Im gonna need a diagram or a very detailed explination of the wiring at all 4 or 5 terminals of each relay to help.
Its probably just somthing you didnt account for in the logic of your relay circuit and could be fixed with a diode somewhere.

[mrltd]

I tried a diode in a few places. Didn't help any. Damn,thought that was pretty detailed....here's a rough schematic...

[gadget73]

Actually you only need 2 relays to do what you want.
**edit**
ok that schematic isn't right. Let me see if I can hack this up in paint and make it not retarded.

See if you can read this. Its my horrible chickenscratch scanned in. I'll see if I can do this up in some more legible format later

http://lunar.gadget73.com/images/schematic.jpg

I'm pretty sure that should work. Relay 1 has the normally closed contact (87a) going to the low speed, and the normally open going to the high speed. The switched contact (30) gets its power from Relay 2. Theory of operation is something like this

Relay 1: not energized
Relay 2: not energized
No fan runs

Relay 1: not energized
Relay 2: energized
Low fan

Relay 1: energized
Relay 2: energized
High fan

Relay 2 must have power for the fan to work. The only way high fan will come on this way is if the AC is switched on. This will supply power to both R1 and R2. If the fan controller comes on, it supplies power only to R2. You can flip around the fan outputs so AC runs on fan low and the fan controller kicks into fan high if you'd like. SImply reverse connections on 87 and 87a on the top relay.

[mrltd]

Makes sense...less relays are better.

The problem I saw with that other schematic from the S10 forums is that it looked like the low fan was on constantly...I spent way too much time messing with that friday....

[gadget73]

Yeah, I realized that after I looked at it more. That might work for some fans, but I know if you try and energize the high and low contacts on a Ford fan it just sits there and sucks up crazy power. Tried it on mine and the ammeter on the 30 amp supply slammed and voltage dropped to about 10v from 15. Another issue with that schematic I drew up is that its not keyed power. Depending on the setup of the fan controller, it could stay running after the engine is off, but that would be easy enough to fix. Either make the fan controller itself run off key power, or wire in a third relay between the battery + and control that with keyed power.

[85crownHPP]

are you using single pole double throw relays? they have two outputs - one is always a closed circuit, untill the relay is energized - then the relay 'switches' the output over to the other terminal.

With these, all youd have to do is power the thermostat controlled relay through the normally closed circuit terminal of the AC relay. This way, whenever the AC relay kicks on, the low speed fan will shut off, since the thermostat controlled relay is no longer getting a power supply.

This is how I wired my foglamps to go off when the high beams come on.

[gadget73]

Yeah, that schematic is SPDT relays, standard Bosch ones that are avaliable anywhere. The way its wired, the low is on the normally closed contact, and the high is on the normally open, so putting power to the top relay flips it from high to low. The bottom relay just takes the load off the fan controller itself and switches +12vdc on and off. The diodes are there to keep the fan controller from kicking the AC on, and to keep the AC from feeding voltage backwards into the fan controller.

[mrltd]

OK, well remember the schematics for Scottfest when you guys clean up the wiring in the superlinc...

I dunno why I overcomplicated it so much...prolly because I was tired as hell..