Bypass Switch for an AC Radiator Fan
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=94879
Printed Date: May 12, 2024 at 2:44 PM
Topic: Bypass Switch for an AC Radiator Fan
Posted By: swede
Subject: Bypass Switch for an AC Radiator Fan
Date Posted: June 17, 2007 at 9:10 PM
I'd like to install a bypass switch to turn the AC pusher fan on whenever I want, such as when sitting in traffic, etc. The fan is set to come on when the AC is on so I don't want to damage the AC fan relay.
I can activate the fan directly with a switch from the battery (through another relay?) but am afraid of 12v going back through the + lead from the original AC fan relay. Is this a legitimate fear and if so, how do I remedy it?
Hopefully this makes sense....I searched the archives and found nothing that sounded similar so 1000 pardons if this has ever been asked before.
Thanks.
-------------
Subtlety is EVERYTHING.
Replies:
Posted By: hotwaterwizard
Date Posted: June 19, 2007 at 12:34 AM
 ------------- John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !
Posted By: swede
Date Posted: June 22, 2007 at 12:46 PM
Thanks much hotwaterwizard. Looks like what I needed.
 ------------- Subtlety is EVERYTHING.
Posted By: dualsport
Date Posted: June 23, 2007 at 11:09 PM
If you do this, be sure to use a high current relay and heavy gauge wiring for all your connections, because the fan draws a hefty amount of current. If any of your connections are marginal, they'll heat up and fail.
An alternate would be to find out the switching method for the original fan relay, and tap into that to switch on the relay. That'll be low current and one less relay path to go through, just using the one relay.
You do need to be more careful because you don't want to mess up your existing relay control; you'll have to test it out fully to see if it's using a switched ground or switched 12V. If it's ground switched and you try connecting 12V to it, it'll surely blow.
If you're not comfortable testing for it, using a second relay would be safer, or else find someone that can check it out for you first.
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