Any electrical gurus out there? I need help.

US 1990 Integra 3 door GS. I am trying to determine why my radiator fan will not come on when the engine is hot (above 194 deg F), allowing overheating if A/C is not on. I don’t think it ever worked from new in 1990, since I mostly drive on the highway the well designed all aluminum engine seems to self regulate temp without need of a fan. If stuck in traffic, it has overheated before switching on the A/C to bring to engine temp back down. Also, intermittently, the condenser fan will come on sitting in the driveway (without the engine being hot, even cold).

A/C side of system works fine, both fans come on when A/C is on, thus assuming relays are functioning. Jumping connectors on back side of relay plugs also brings fan on.

I have the correct OEM Acura service manual for my car. I tried jumping the “Coolant Temperature Switch” (aka thermo switch) with ignition on, neither fan will come on. Checked all my ground wires have continuity to ground. I do NOT have continuity on the YEL/GRN at the R-Fan relay to the YEL/GRN terminal of the CTW (Thermo switch)(IGN on and off). I tested the “Cooling Fan Timer Unit” pinouts as described as well as the Diodes test, all seems to be functioning properly at this time. Still no fan.

I’ve attached the diagrams I’m going by, I’d appreciate some expertise.
[img]uploads/bikermark1/7D9EA_A-C_Diagram-s.jpg[/img]
[img]uploads/bikermark1/21FD4_Timer_Unit-s.jpg[/img]

Front-wheel drive cars have electric fans because the
engine is usually mounted transversely, meaning the output of the
engine points toward the side of the car. The fans are controlled
either with a thermostatic switch or by the engine computer, and they
turn on when the temperature of the coolant goes above a set point.
They turn back off when the temperature drops below that point. Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch.
This clutch is positioned at the hub of the fan, in the airflow coming
through the acura radiator. This special viscous clutch is much like the viscous coupling</span> sometimes found in all wheel-drive cars.

love the diagrams thank you.

have you tested to see if the temp sensor has ground?

and to see if when the engine is hot if it is switching?

also you can unplug that sensor and short the pins (making the system
think its hot) (be sure to have the keys in the run position)

doing so should turn on the fan.

your telling me that both fans work with the AC

that also tells me that you (NOT) getting the trigger ground signal from your temp sensor yellow/green wire.

when the ac is on it will bypass the temp sender request and ground the fan relay.



If you find the chassis ground is at the temp plug but shorting it with
the key in the run position does not turn on the fan the you will have
a bad wire inbetween the temp switch plug and the fan relay.

I think you have a bad wire inbetween the temp switch plug and the fan relay. Try also to check the thermo switch ground.

Have you checked the Cooling fan relay?

Good post and I like the diagrams also..keep up the good answers on the posts...

WheelBrokerAng :)