Fan Cycling Problem.

[Matt]

I've got an issue with my fan on my 08 KW T660 ISX. Most of the time it works normally, only cycling when engine coolant temp goes to like 210 BUT once and a while it has a "fit" where it engages for no reason and will run for say 10-20 seconds, cuts out and only a few seconds later cuts in and repeats this for 3-4 cycles. It does it weather the AC or defrost is on or off, all temps will be normal operating. It also kicks on the "fan on" light on the dash and because of that, I feel like the ECM is commanding the fan on. I've changed the air fan solenoid on the side of the HVAC box and i've checked connections to the High pressure AC switch, the switch near the AC compressor, Intake Air sensor and coolant level sensor on the coolant tank all with no indications of bad wires, plugs etc.

Since my Inline 6 will be here today, is there a way to use Insite to monitor what is triggering the fan on while i'm going down the road so i can catch the problem as it's happening and diagnose the issue?

[smorgan87]

What is ur air psi when it kicks on? Mine engages if air drops to 90ish. Could possibly have a loose wire on ur fan solonoid which could be goin bad

[Matt]

Air PSI is always up over 100, basically normal operating range.

[Nilao]

I believe the parameter you want to monitor is fan state. It will tell you what system is causing the ecm to engage the fan.

[Matt]

Thanks Nilao. DHL didn't deliver my inline on time so it'll have to wait till I get back from WI but I'll post what I find when I can check it.

[Dcline1011]

I have a ism doing same thing

[Matt]

OK folks, finally got Insite to run with my new Inline 6. The fan acted up pretty well constantly on the last trip. Took the truck out for a test drive. It was good for a while but then low and behold, Fan state says Air Conditioning Pressure Switch, I also monitored the AC Pressure Switch state and it flip flopped quite a bit between ON and OFF when it was having its little "fit". Found the pressure switch above the compressor and pulled the plug, fan came on and then jumper'd it and the fan stayed off, wiggled the shi#t out of the wires and it was good. Do you guys think it's the switch? or maybe the plug isnt making great contact in the end of the switch? Can that switch be replaced without evacuating the refrigerant? All of this testing was done with the HVAC system OFF.

[Chamberpains]

Most AC pressure switches can be changed without evacuating the system. Including the high pressure fan switch. They have Schrader valves like the valve that's in your valve stem in tires, behind them. I say most because sometimes you will find somebody will rig one together because the Schrader valve was shot and not put a new one in or they will sometimes stick. It's always a possibility. you'll get a little Spurt of freon that comes out but that should be about it. Keep your hands away from the freon it stings a good bit on bare skin.
Yes, switches do go bad where they flicker intermittently. If you checked the wiring thoroughly and the plug checked out. then I would suspect the switch is shot.

[Matt]

I'll give the switch a go. I'll post the results.