On a 05 t300 propane truck with a pacard engine the fan clutch wasnt working it wouldnt hold. So i rebuilt it. The first time i started it cold it was on then after a miniute it disingaued. The first day it was cold out and driver said it worked ok days later it wormed up and didnt come on when it needed to but would come on some times when going slow when he put on the brakes when temp was low.It dosent have a fan switch would it be hard to put one on it?
You'd be better off to fix the real problem. You'll need to get a wiring diagram and understand how the fan clutch system works. It sounds like you have a control issue, but it's hard to say. If you can find someone with the Paccar software, they should be able to command the fan clutch to actuate. That would speed up the diagnosis.
This^ That fan is controlled by the ECM using engine sensor inputs. Coming on with the brakes may be an extra retarder feature, like having the fan on with the jakes on bigger trucks... Unless you're plugged in... you really don't know. Oh, what was the temp of the engine when "It didn't come on as needed" ? Had a guy screaming at me the other day because his 3406E didn't start the fan til it was 200 degrees according to the dash gauge. Fan switch was 195 deg and his electric gauge was reading 5 deg high. If it doesn't boil... don't bother me.