Troubleshooting fan issue

[Tom _M]

Have a '99 Honda CRV where the the a/c and cooling fans don't want to work, and am struggling now to find out what's causing the issue.

If I unplug the connector from the fan sensor switch that goes into one of the coolant lines and bridge the connection with a paperclip, then with engine off and a/c switched on, then both fans will operate. If engine on (but no a/c on) and connection bridged, then both fans also on. That led to to think was a faulty switch, so got a replacement, fitted it, and still exactly the same issue... Thought it might have been a dodgy switch, so tested in some boiling water with multimeter doing continuity testing (it's amazing what you can learn from Youtube) and found that it opened up at about 95 degrees, so seems to be working as it should. Have sat with engine up to temp (middle of gauge) and driven around, and fans still won't seem to come on.

So am still stuck with no working fans, which won't turn on when a/c turn on (as they should) and won't turn on even when engine up to temp.

Any thoughts on what might be causing this?

[Penelope Stopit]

There may be no water around the fan temperature switch

[GreenV8S]

I guess the switch you're referring to is some sort of 'otter switch' which closes when the coolant goes over a certain temperature.

You've tested the old switch off the car, but have you tested what they're doing on the car? If not, it would be worth measuring the resistance across the sensor with the wires disconnected and see whether the switch closes when you think it should.

So far you haven't mentioned any overheating symptoms so I wonder whether it has actually reached the conditions where it needs the fans on.

[sunbeam alpine]

If the temperature only goes up to the middle, the cooling fan probably won't switch on - that's only going to happen at a higher temperature, so it's possible there's nothinng wrong there. You need to leave the engine running with the car stationary until the temperature rises above the middle.

The fan for the AC could be an unrelated problem - if the system needs re-gassing the a/c compressor should shut itself off, and maybe the ventilator gets shut off as well.

So it could be one or two separate faults.

[Tom _M]

Bloody electrics make my brain hurt...

I 'think' there is coolant flowing past the sensor as had to remove newly installed switch to check it when system was full, and enough came out anyway.

I haven't tested the switch in situ to be fair, no, so that would be worth a check I guess, though not sure if can get probes into the somewhat awkward space where it's situated. Temp gauge hasn't gone past the middle of the range, so perhaps isn't getting hot enough when in use to close the switch. According to specs should close at 90-95 degrees, which ties in with my stove-top home test. Not sure what temp it should be running at normally though?

Could well be a different a/c fault then that's throwing up these issues then...