wiring 2 speed efan w/ controller

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=122955
Printed Date: July 05, 2025 at 5:27 AM

Topic: wiring 2 speed efan w/ controller

Posted By: 99bigdreamer
Subject: wiring 2 speed efan w/ controller
Date Posted: August 03, 2010 at 10:06 AM

I searched and found some good threads but they were closed and none answered this specifically.
I have a Taurus 2 speed fan that I am putting in a 1990 gmc pickup. I have a Hayden 3647 fan controller with temp probe in radiator. My ultimate goal is to have one speed of fan run with temp probe and the second speed run with A/C. Both the controller and the A/C are + switched. I think I can run the low speed through the controller because it has a 40 amp relay built in and low only pulls ~20 amps (running). To run the high speed though I will need to wire 2-40's together to handle the ~35 amperage (running). If someone can help me with this, using standard 40 amp relays (spdt) and the controller I already own, that would be fantastic! Thank you.

Replies:

Posted By: 99bigdreamer
Date Posted: August 03, 2010 at 10:08 AM

Here's a link to the controller I have.
Hayden 3647

Posted By: 99bigdreamer
Date Posted: August 03, 2010 at 10:26 AM

I found this diagram that looks like it would work but I need an additional relay on the high speed side.
posted_image

Posted By: 99bigdreamer
Date Posted: August 03, 2010 at 10:58 AM

also, maybe like ckeeler suggests here:
https://www.the12volt.com/installbay/forum_posts.asp~TID~107972~KW~fan~PN~0~TPN~1

I just don't know if the temp switches he references are + or - switched.

Posted By: oldspark
Date Posted: August 03, 2010 at 9:13 PM

Use a properly rated relay - using 2 in parallel leads to premature failure (different closing times) and if one fails, the other burns out. (I use a 60A changeover relay for my battery isolator.)

Posted By: 99bigdreamer
Date Posted: August 04, 2010 at 6:45 AM

I fully intend to use a proper one but, I have to order it. Right now I just want to 'get by'

Posted By: i am an idiot
Date Posted: August 04, 2010 at 7:56 AM

https://www.the12volt.com/installbay/forum_posts.asp~TID~98402~PN~2~get~last

Posted By: oldspark
Date Posted: August 04, 2010 at 8:17 AM

I've seen relatively cheap continuous rated relays of 100A to 250A for ~$20-$25 stateside. But may as well order a 60A or 140A etc (which are almost "regular" relay size).