The fan solenoid has a normally on and a normally off setting. Look at the instructions that came with the switch.

There should be two places that you can hook up the inlet air line, and one exit line to the clutch. It may be hooked up backwards, and may have been that way when you bought the truck.

The correct setup in most applications is: when the key switch is on, the fan will rotate freely, and then will engage with the switch turned off. If your fan turns freely with the switch off and the air built up, then the fan switch is hooked up backwards.

Some switches change the on off settings by the electrical plug, but most just have a total of three places to hook up air lines, and you use the correct one for your application. They are easy to get backwards.

My fan clutch on my 1995 FLD120 is a Kysor and is presently stuck on like yours might be. With the hood open turn on the key but don't start the engine aand see if you can hear an air leak in the clutch like mine. If not, now turn the fan by hand with the key still on - it should turn. If not it is stuck on. I bought a rebuild kit from Freightliner for $115 but haven't put it on yet.

I would guess it is the fan clutch. That happened to me once with a Detroit. I nearly froze until I could get it fixed. :? There is nothing like being in a foot or so of snow and having your heater blowing out ice cubes. :shock:

I once drove home from Baltimore with no heat,the temp was 38 when I left and sunny,kept cab warm until the sun went down for the last 2 hours,basically wrapped myself up in a sleeoing bag........ah the memories

I have tried changing the sulinoid, i checked to make sure it was hooked up right by turning the key on, everything seems to be working fine. Ive come to the concultion that its a wiring problem. Im just gonna rewire the whole thing. Thx for the tips guys

Have you checked the manual switch in the cab?

Update on my stuck fan clutch:
The fan clutch was working before the truck was parked for six months. Today I went to mess with it and decided that the air leak wasn't big enough to cause it to stop working. I read in one of the manuals I have for it that the clutch can get "stuck" and tapping it with a hammer would get it loose again. I hate to play "hammer mechanic" but damned if tapping on the three back pates that hold the lining in didn't get rust powder puffing out. It didn't immediately start turning right by hand but after starting it and running down the road a bit I noticed my shifting sucked - with the fan off it takes about twice as long as before for the engine to slow down enough to catch the next gear :shock: . BIG difference on running downhill too - that fan was soaking up a lot of horsepower and now I have to use the brakes a lot more.

It is amazing what you can do with a hammer and brute force. :lol: