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Low speed relay/resistor Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Sun, 8 Mar 2009 11:01:21 In Reply to: Radiator Fan not Working - Relay or Switch or What?, gman, Sun, 8 Mar 2009 04:26:32 Members do not see ads below this line. - Help Keep This Site Online - Signup |
First - I assume the temp gauge is going high when the car is stuck in traffic/moving slowly. If it is overheating at speeds over 30 mph, it's a radiator/water pump issue.
OK, assuming it overheats when idling, it is probably a fan issue. The first thought that comes to mind is the low speed resistor. The fan runs at two speeds - low and high. Low comes on first, by switching 12 volts through a resistor (the metal rectangle bolted to the fan). With the voltage drop across the resistor, the fan runs lower (low speed). If the car keeps heating up, the high speed relay switches out the resistor, and with 12 volts on the fan, it runs at full speed.
If the resistor has failed open, or the low speed relay is bad, then the fan doesn't come on at low speed. The fan is designed to come on slowly first, then full speed. A motor that isn't turning takes A LOT of current to start running; if it is running already at slow speed, it doesn't take a lot of current to speed up. If the low speed circuit is bad, the large inrush current will blow even the 30 amp fuse. Now with now radiator fan, the car will overheat.
However, if the radiator fan is getting tired, it can also take a lot of current to start. However, I'd check the low speed resistor. With the car off and cool, measure the resistor with a meter. If it is an open circuit (more than 3 or 4 ohms, actually), then the resistor needs replacement.
When the engine temeperature goes high, the AC automatically shuts off to reduce the heat load on an already hot engine.
posted by 192.249.4...
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