Classic cars forum & vehicle restoration.
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Ray White
Joined: 02 Dec 2014
Posts: 7075
Location: Derby
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 Posted: Mon Jul 07, 2025 1:34 pm Post subject: Electric fan |
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I have read how an electric fan (Kenlowe etc) may work incorrectly if a "normally open" relay is not used.
I am informed that if a "normally closed" relay is fitted, the fan may come on with the ignition and go off when the selected temperature is reached...which is obviously no good at all.
Is this information correct or not, please? |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4231
Location: South Cheshire
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| Posted: Mon Jul 07, 2025 1:48 pm Post subject: |
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Ray
the question or observation doesn't make much scene  regardless of the relay, if the fan supply is via the ignition supply, if the ignition is off the fan has no supply so can't work, if its direct (like horns were) it will operate regardless of the ignition state.
The latter is more common, certainly on modern vehicles, I often hear the fan on my modern running for a short while when the engine if off. |
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Ray White
Joined: 02 Dec 2014
Posts: 7075
Location: Derby
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| Posted: Mon Jul 07, 2025 2:40 pm Post subject: |
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| ukdave2002 wrote: | Ray
the question or observation doesn't make much scene regardless of the relay, if the fan supply is via the ignition supply, if the ignition is off the fan has no supply so can't work, if its direct (like horns were) it will operate regardless of the ignition state.
The latter is more common, certainly on modern vehicles, I often hear the fan on my modern running for a short while when the engine if off. |
Thank you Dave. I couldn't quite understand it so I Googled the question and this was the reply:
"
Relay-Controlled Circuits
A normally open (NO) relay is the correct choice for a 12-volt thermostatically controlled fan. This type of relay will allow the fan to turn on when the temperature reaches the set point, as the thermostat closes the circuit, activating the relay. A normally closed (NC) relay would be the opposite, meaning the fan would be on by default and turn off when the temperature is reached, which is not the desired behavior for a cooling fan. " |
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