Rotting Prelude

Car is a 1994 honda prelude Si H23A1. Cooling fans are no longer turning on, temp guage will go over halfway and they do not come on. However if I turn on the AC both fans will work without issue, which has me very confused. The CTS sensor is a few months old, if I jump the connector with a paper clip fans still wont turn on. The 3 fuses that are on the cooling fan circuit are good, I would assume the relay works as well since the fans work when the AC is on. Any thoughts? can provide more info if needed.

DCFIVER

Switch "A" is in the lower portion of the thermostat housing(by the intake tube ,towards the back of the engine bay) and is the one that commands the fans to initially turn on. Is that the one thats new?

On this Honda there are 4 different coolant temp sensors, make sure youre checking the right one.

muellersfan

Start with a cool engine:

Top off the reservoir and radiator with coolant.

Turn the climate control to max heat to allow coolant to circulate through the heater core.

Bleed the cooling system thoroughly.
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Do the fans now turn on when the engine is fully warmed up?

Does the engine still overheat?