My ‘49 Hudson with a 500 Caddy engine keeps blowing the fan relay. Only driving in backyard on and off the lift Any ideas why it would ?
Does current rating of the relay match that of current draw of the fan(s)? Is there more than one fan running off of the relay? If so, how is it wired up? DC motors typically have an in-rush current that is greater than the max stated current draw, but typically this is not an issue as the in-rush current is momentary. Is the orientation of the relay specific (e.g. some relays need to be mounted “upright”)?
Check amp rating of Fan , Correct wiring size Ga for Length of wire , My Spal fan pules close to 50a Typical bosh relays are 15 amp & 30 Bigger amp relay have 1/4 inch spade Terminals or screws
Ziggster hit it.... some Cooling Components fans draw 60amps on startup.... those 15a contacts dont like the draw.
The guys hit it spot on in that the amp load of the fan is more than the relay is related for and or more than the gauge of the wire can handle. There are hundreds of wire gauge vs amps charts on the net and I don't think any two that weren't copied from each other are exactly the same.
this relay handles high amp startup rush, also has a diode built in to avoid engine run on due to the fans producing electricity. I've used it on several builds.
These fine fellas have got the basics covered. An electrical circuit that 'blows' is not sized properly or shorted. I have to ask how it's set up also, along with the other questions. If it's thermostatically controlled, how is it even engaged ? It shouldn't get hot enough to trigger. If it's a switch you control, it wouldn't need to be driven or even running. Can you describe the whole circuit? Power input to relay Power output from relay to fan Relay Fan Trigger and ground How fan is grounded.
For my cars with electric fans, I use a Volvo 2-speed fan control relay. It is specifically designed for controlling an engine cooling fan. It has large copper contacts and even works well with a single speed fan.
Maybe he found the spot on the wires between the relay and the fan where the insulation was cut or melted through, and the wires were grounding out.
70 amp relay with wiring instruction: https://painlessperformance.com/product/70-amp-fan-relay-kit-part-no-30100/ @airbrushguy , have you resolved the fan relay problem?
The two part numbers I have are 3523872 and 94432933. I get them out of 90's Volvos at my local Pick and Pull. I also take the mating connectors and as much wiring as I can. I have about half a dozen of them and they are easily available on Ebay or AutohausAZ. Here's a wiring diagram as well. For the temperature switch I use a BMW dual 91/99C unit.
You can use any Normally Open temperature switch because it's the grounding of the wire that triggers the relay. You can use a single temperature switch and run your single speed fan just fine. I have a 2-speed fan, so I use a dual switch. You can use a manual switch to bypass the temperature switch. If you google Volvo fan relay you will be linked to several videos on how different people installed these relays. Here's the schematic of the internal wiring of the relay showing how it works.
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