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Jul 21st, 2025 | | | | Joined: Feb 2006 Posts: 150 Shop Shark | | Shop Shark Joined: Feb 2006 Posts: 150 | I'm installing A/C in my 54 3100. The engine cooling is being done via an electric fan which is wired via a relay and is controlled by a single wire coolant sensor switch. I have also added an manual override switch to that configuration.
I know I can wire the A/C compressor via "yet another relay" to also operate the engine cooling fan as required for the A/C.
I have heard that you can "with one wire" control the fan by splicing the compressor wire to the engine cooling sensor switch. This wire, I think has a diode in it. Can this be done? Pros/Cons?
Thanks | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Relays are cheap. I'd suggest installing a dedicated relay triggered from the compressor power wire in parallel with the relay controlled by the temp switch. The electric fan operation becomes an either/or situation, controlled by engine temperature or air conditioner use. Be aware that most original-equipment electric fan switches turn the fan on at 220 degrees, so you'll need a good 15 pound or higher pressure radiator cap to allow the coolant to get hot enough to turn the fan on. Some aftermarket fan switches are adjustable, so the fan can be set to turn on at a lower temperature if desired.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 | I agree with Jerry. The fan needs to be in an either/or condition. The diode is installed in the fan circuit as a blocking device. When you cut power to the engine the fan will continue to turn for a short time and will act as a generator. That voltage will be enough to keep the engine running in a rough fashion.
Six volt guy living in a twelve volt world
| | | | | Joined: Jun 2010 Posts: 1,001 Shop Shark | | Shop Shark Joined: Jun 2010 Posts: 1,001 | I am installing a/c in my 52 presently. The electric condenser fan will be controlled via a trinary safety switch. The switch mounts on the receiver/dryer via a schrader valve. The switch has three purposes: activate fan, low and high pressure cutoff. The fan will be powered via a relay. Old Air Products has all the stuff. | | | | | Joined: Feb 2006 Posts: 150 Shop Shark | | Shop Shark Joined: Feb 2006 Posts: 150 | Thank you for the direction. I well be adding the relay today and completing the wiring portion of the job.
Thanks again | | |
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