I recently had to change the water inlet hose on my 1999 Honda Accord EX (4 cylinder). As a result, I decided to flush the radiator, change the thermostat and thermo fan switch. The problem I am facing now is the radiator fans do not turn on. They turn on if I turn on the A/C. Therefore, the fans are not broken.

When I flushed the radiator, I made sure to bleed the system. I purchased an aftermarket fail safe thermostat and thermo fan switch from Autozone. The car doesn't overheat, but I am concerned that the temperature gauge is not working properly, which may lead to a blown head gasket. Also, I noticed that the temperature does not reach the point originally when the car is fully warmed up. It runs slightly cooler, which I suspect is due to the aftermarket thermostat.

I just want to point out that the water pump and timing belt were changed about 20K miles earlier.

I figured the car should overheat if my radiator fans don't turn on. My thermo fan switch was faulty about 2 years ago and the car would overheat during long periods of idle. This time the car will not overheat even though the fans don't turn on. Does anyone have any ideas why my radiator fans are not turning on?

 

You already answered your own question. Get a Honda OEM thermostat and fan switch directly from Honda. Aftermarket cooling system parts can be a crapshoot at times and it's not really worth the risk that they either won't perform properly(as is the case in a thermostat) or that they simply won't last long at all.

 

^This!

 

Before I go and buy the oem thermostat and fan switch, I want to make sure those are the culprits for why the fans are not turning on. I'm started to think I may have some air in the system. Any ideas on how to troubleshoot/test whether it is a thermostat/fan switch problem or a bleeding issue?

 

If it's running too cool, I don't think you'd be seeing air in the system - it's probably due to an incorrect/damaged thermostat and/or fan switch.