My car overheated about a month ago. Replaced thermostat, both switches, heater hose, and bled the system. The cause of overheating was thermostat, but noticed the fans were not coming on either.

Fans still wont work. jumped connection at thermostat housing switch and fans come on. Tested both switchs in boiling water and the switchs are bad.

Does anybody know why both new switches would test bad.

Also during this diagnosis ran the a/c and both fans come on, but shut off shortly after they come on, is this normal.

 

So both switches are bad, and they're both kinda new? That sounds unusual.

 

Wrong thermoswitch may have been used. Thermoswitch B is set to close at 225F from memory and Theremoswitch A closes at 194F. If wrong switch were used, both would seem bad if tested at correct temp. Temp rating is usually stamped on switch somewhere, but may be in degC instead of degF. 90C=194F.

good luck

 

Switches are right, both are different sizes, cant switch them around. Checked them in boiling water. Checked an old temp guage switch this way and the test was good. Should the fans cycle on and off when the a/c is going. Maybe the relays on the radiator are switched around? Could excessive voltage ruin a switch?

 

There are separate relays for each fan, but you said both fans run when Temp Switch A was jumpered. This says relays and fans are OK.

So you have bought two bad Thermoswitch A's in sequence. Were they OEM units? Time to get a better quality switch.

good luck

 

would a bad radiator fan control module fry the switches.

 

Not IMO...do you have an IFR Temp reader?

Also know the bleeding of the coolant is a bit tricky. Can you try that again...or at least tell us how you did it the first time?

 

If fan control module were faulty, fans likely would not run at all. Fan control module supplies power to actuate the relays which drive fans. Since fans work w/ AC, problem lies elsewhere.

Agree w/ PM on insuring that system is bled correctly. This can cause appearance of overheating; temp gauge goes high (probably no water flowing over temp gauge).

good luck