3 replies to this topic

[summit mechanic]

hey i have a problem with a 98 ch600 the air clutch for the cooling fan wont disengage i can provide a gound to the air switch on the drivers side of the radiator and it will turn off but the truck wont do it on its own i suspected a temp switch but talked to a mack dealer and they told me it was controled by a computer based on the values of multiple sensors is this true or is there just one switch?

[Mackpro68]

hey i have a problem with a 98 ch600 the air clutch for the cooling fan wont disengage i can provide a gound to the air switch on the drivers side of the radiator and it will turn off but the truck wont do it on its own i suspected a temp switch but talked to a mack dealer and they told me it was controled by a computer based on the values of multiple sensors is this true or is there just one switch?

The engine ECM tell it to come on, it actually grounds the circuit inside of the ECM to engage the fan. The ECM looks at coolant temp, AC high pressure and intake manifold temp to know when to engage.

[summit mechanic]

so it could be one or more of those sensors not functioning properly or a malfunctioning ecm?

[Mackpro68]

so it could be one or more of those sensors not functioning properly or a malfunctioning ecm?

Yes, Check the small fuse box (if this is an ETECH engine)under the hood on the firewall, look at fuse # 41 i think. This sends 12V to the fan circuit. I had a truck the other day having high AC pressure due to when defroster is turned on the AC compressor was engaged but the expansion valve was stuck closed causing high pressure. Even after the engine was shutoff for several hours it still had high head pressure.