NBC- Is the operation of an electrical switch impacted by heat? |  |  |
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I installed an in-dash switch to manually control an oil cooler fan on my 88 911. It is a simple on and off switch wired to a fuse block and a relay before the fan. The switch and fan have worked great (for 24 months or so) when the car is cool and the engine is off. But lately, when I press the switch and the engine is starting to get hot (driving in stop and go traffic), the fan does not always go on. I should clarify, if I push the switch 3 or 4 times, one of the times the fan will go on. It is hard to hear the fan go on in traffic, so I can only tell by pulling over and getting out of the car for a listen. I confirmed that the fuse is not blown.
I have a jumper where I can bypass the switch. I will try that next to see if it is the switch, fan or relay that is impacted by the heat. I am not sure if a switch remote to the fan can be impacted by the heat of the engine cooler. Any risk of jumping the switch when conditions are hot?
I have a jumper where I can bypass the switch. I will try that next to see if it is the switch, fan or relay that is impacted by the heat. I am not sure if a switch remote to the fan can be impacted by the heat of the engine cooler. Any risk of jumping the switch when conditions are hot?
If I understand correctly what you are doing you are running the full current of the fan through the switch. That's too much current and the switch will arc every time you turn it off and slowly erode the contacts. You need to put a relay into the circuit with the proper components to eliminate arcing.
Quote
Tony in Whittier
I installed an in-dash switch to manually control an oil cooler fan on my 88 911. It is a simple on and off switch wired to a fuse block and a relay before the fan. The switch and fan have worked great (for 24 months or so) when the car is cool and the engine is off. But lately, when I press the switch and the engine is starting to get hot (driving in stop and go traffic), the fan does not always go on. I should clarify, if I push the switch 3 or 4 times, one of the times the fan will go on. It is hard to hear the fan go on in traffic, so I can only tell by pulling over and getting out of the car for a listen. I confirmed that the fuse is not blown.
I have a jumper where I can bypass the switch. I will try that next to see if it is the switch, fan or relay that is impacted by the heat. I am not sure if a switch remote to the fan can be impacted by the heat of the engine cooler. Any risk of jumping the switch when conditions are hot?
More than likely the fan is affected by the heat. Is the fan you are using intended for that kind of usage? The radiator fan motor -- for example -- has to work start up even if it is hot as of course it is *behind* the radiator and heated by the air passing through the radiator. The air it pulls through the radiator has to "cool" the itself remove the heat that the motor generates as it runs.
Does the oil cooler fan have some kind of thermostat/temperature sensor control to cycle the fan motor off if the oil temperature drops below a certain threshold even if the switch is still on? If the fan runs all the time the switch is on the fan motor may not be intended for that severe a duty cycle. You may be facing a fan motor that is nearing the end of its life.
The fan is a Spal pusher. It is a plastic bodied fan mounted on the front metal rim of the oil cooler (ahead of passenger side front tire). The air flow is toward the rear. I don't remember the exact model or size, but between 5.2" and 6.5" (from Spal website). Control is only from the switch or relay. No temperature control, unless it is an internal motor circuit. Will that motor have it? I dont see a schematic on the site.
Not sure on fan application, when I put it in I was replacing a seized temperature controlled metal fan. I abandoned that circuit and opted for manual control with a relay and separate fuse block.
I will jump the switch the next time it fails. I will also see if the fan is real hot to the touch.
Thanks for the suggestions.
Not sure on fan application, when I put it in I was replacing a seized temperature controlled metal fan. I abandoned that circuit and opted for manual control with a relay and separate fuse block.
I will jump the switch the next time it fails. I will also see if the fan is real hot to the touch.
Thanks for the suggestions.
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