testing Coolant Temperature Switch for 93 Escort

Hi;
I have a 93 Escort. Electric Fan comes on with air conditioning, but doesnt come on otherwise. If I remove the two wire connector from the coolant temp switch, it comes on. How can I test this switch? Are
there any ohm readings I can take? Thanks for any help
Pat
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I think you just did... ;-)
A lot of those fan switch circuits are 'ground the lead to turn off the fan' and the theory is if the switch fails it will fail open to leave the fan on. But in reality some fail grounded and the fans do not come on.
If they're coming on when you unplug the sensor, that tells us the fans and the control box works, and that pretty much leaves the temp switch as the culprit.

Yes, but I'm not sure if the switch is supposed to switch between the two pins, or one to ground when cold and the other when hot, etc. A spec sheet for the sensor will tell you the wiring diagram and the proper actuating temp range.
One thing to consider: If the car's thermostat is stuck open and the engine takes a long time to warm up, that can fool you into thinking it's the fans not coming on - but the fans will never need to come on if the engine never gets hot...
Invest in a good thermometer to tell what's going on. For around $10 you can get a "Chef's Instant Read Thermometer" which is the 6" stainless steel spike with the 1" dial thermometer on the end - plenty accurate for reading the coolant temp with the car parked and the radiator cap open. The same thing but with a digital electronic readout is around $20.
If you want to read the temperature inside a closed and operating cooling system you need an infrared non-contact thermometer. They run $60 - $100 for the basic units, but they are literally worth their weight in gold as a diagnostic tool. The better ones have a low-powered laser pointer built in so you can "see" exactly where you are getting the temperature reading from.
I use mine all the time looking for potential trouble in energized power panels - it will easily show you where a busbar joint or a cable lug is loose and getting hot, without trying to touch a metal thermometer probe to energized parts with 240V or 480V AC on them.
--<< Bruce >>--
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Go over to http://www.feoa.net and look in the fourms.
Download the factor service manual and print out the schematic and pinpoint tests. This has been discussed many times there before. Please do not add another redundant post there, your question has been answered many many times.
In general, it's often a relay. There is a well posted mod there to put in a more robust relay that has larger amapacity contacts in it. Could be a bad sensor, bad sensor electrical connection (the first place I'd look), or dirty contacts on a relay (I'd bench test the relay and if it still moves then clean the contacts inside if it). but that's just me, most people don't know how to bench test a relay or clean internal contacts in one).
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