Not sure where the thermoswitch is on a 90, but my bet is that this
switch is shorted (constantly on) or the wire from it has shorted to
ground.

tegger.com has a cooling section that may help you.

Remco

If it's a 90, I just went through finding that thermo switch myself...

It's under the intake manifold, next to the oil filter.

My various manitenance manuals either say it's located at the bottom of
the radiator or on the thermostat housing. On a 90 Civic EX, (pretty
sure CRX is different) it's at neither place, but under the intake
manifold next to the oil filter... the only way to access it as far as
I know is from beneath. Need to wrap new switch threads with teflon
tape per the Helm manual. I got mine at Napa and it came with new
o-ring.

Good luck.

A friends 1990 4S manual has teh radiator thermo switch on the lower
left, standing in front. It controls a relay that supplies power to the

fan motor. The thermo switch closes to ground when hot.
So either the switch is failed shorted or a  wire is pinched to ground.
The relay could have failed closed but that is a long shot.

Terry