Cooling fan

If the fan fails to turn on at the proper temperature, the problem could be the temperature sensor, the fan motor,( you replace the relay), The circuit wires or the controller .To isolate the cause of the malfunction, attempt to operate the fan by bypassing its control.
On a computer -controlled system, using a scan tool to activate the fan.if the fan operates can do this, the problem is probably in the coolant sensor

I have a 1991 acura integra ls, i can not get the radiator or the condenser fan to work. I have replaced the fuses and swapped the relays with another 91 integra that the fans work on. But nothing helps.

You replied to question about why neither fan coolant and condenser fan not working on 1991 acura integra. You say it could be the coolant switch. where is this switch located and will this also keep the condenser fan from operating? Both fans run when power supplied directly to them indicating the fans themselves are ok.

I meant the sensor at the bottom of the radiator, near the drain plug, but if one of your fans is working and the other isn't, that won't be it.

The fan on the drivers side is the Radiator Fan and on the passengers side is the Condenser Fan, so they both may not work at the same time anyway. They should both be on when the engine and the A/C are on.

First check the #39 & #40 fuses in the underhood relay box. You can test the supposedly faulty fan by unplugging it and run 12v from your battery to the fan directly. If it doesn't run, replace it. If it does, it may be in the wiring/connector to that fan, or it isn't getting a signal to run from the sensor. There is also a resistor inline with each fan that should have between .5-.7ohms (resistors rarely go bad).