Help, fan won't come on

jimaire · **Posted:** Mon Mar 21, 2011 10:53 pm

Can anyone please tell me why the radiator fan won't come on. The fuses and relays are good. No voltage coming to the connector.

papaindigo · **Posted:** Tue Mar 22, 2011 8:12 am

I assume you mean the big mechanical fan just in front of the motor not the AC electrical fan. As nearly as I can tell (see the discussion at http://www.greendieselengineering.com/f ... st/19.page and at viewtopic.php?f=5&t=51618&hilit=flex+fan+flex+fan) that fan will not run unless the coolant temperature exceeds 225 degrees. Hence there would be normally be no current in the circuit. The fan has a clutch that will engage if the trigger temperature is exceeded. It is not uncommon for the clutch to fail, relatively simple test methods are posted, in which case the circuit would have current but the fan would not run due to clutch failure. If you run the test and get no current then you likely have a bad temperature sending unit but I don't know whether the sending unit on the tstat housing does double duty (operates the temp gauge and triggers the relay to run the fan); if it does do double duty and your temp gauge is working then you may have a wiring problem to the fan relay. Best I can do.

jimaire · **Posted:** Tue Mar 22, 2011 8:27 am

Thanks. The problem is with the electric fan in front of the radiator. I have changed out both relays. It can get well past half way on the temp guage and it still doesn't come on. Is there another power panel other than the fuse box that has relays in it?

papaindigo · **Posted:** Tue Mar 22, 2011 5:10 pm

Hopefully someone that knows more than me can comment. In digging thru kapalczynski's flex fan discussion I see a note that the "clutched" fan just in front of the motor is turned on/off by a thermostatic bimetallic spring coil on the front of the fan clutch, no wiring, and failure is usually related to the clutch. Sooo in hindsight I guess the F2 fuse and R34 and 40 relays labeled Radiator fan relate to the electrical fan in front of the radiator which the FSM calls Radiator Fan-Electric (see pg 7-36 of the 2005 FSM) for how it's controled. There is a TSB out for the temp gauge (see the GDE site but I cannot connect right now) as some diesels got gauges set for gas engines but regardless if your temp gauge needle gets just a bit past vertical the fan should come on in low mode. There is a fuse panel to the left side of the dash but I don't see anything that relates to the PCM or this fan.

I'm going way past my expertise but suspect 1) a disconnected or bad sensor likely related to water temp not battery temp or 2) possibly a bad wire between there and either the PCM or the distribution panel both based on the assumption that you have or can check to see that there is in fact no voltage at the fuse or relay when the engine temp is such that the fan should engage. Of course if you have power there and the fan still doesn't work the problem is between there and the fan which could be a bad wire or as simple as a bad fan. Going even further out on a limb, if this was a pre-1975 vehicle I'd test the fan by simply hooking it directly to the battery, if it doesn't come on it's dead. What I don't know is whether or not doing so would cause other problems.

Anyone out there with more electrical smarts than me.

Help, fan won't come on

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