heaters

[RMcGuffey]

I'm having trouble with the intake heaters. They will come on like they're supposed to and you can here them click on and off, but they only come on once. They don't cycle on and off no matter the temp. I've read the service book on them, but I haven't run the voltage tests on them yet. So what actually controls the cycling? I know the sensor in the intake does, but what else? I'm just not sure how the system actually works so it's kinda hard to know where to start. The truck is a 1990 W250. Thanks.

 

[DPinkston]

I think the heaters only cycle once unless the ECM detects the engine has started or the key is turned off then back on. Not sure how the ECM knows the engine is running on a 90 model. Do you have a crankshaft sensor mounted at the damper? If so, then that's how it knows and the sensor may not be reading.

Danny

 

[JLEONARD]

The 90s are different and the sensing temp is different I think. (maybe 15 F)

Hopefully BGilbert or one of the guys with an 89 or 90 will chime in.