anix

Sorry to reopen such a sore subject but I have read threads till I can't see straight and still have not found what I need to help me understand a few things. #1 the manual I down loaded shows a relay, is there one or is it integrated in to the ECM (don't remember seeing one)? #2 if the clutch is variable how does the ECM control the speed. I have no way to monitor when the ECM gives the command to begin speeding up so can I monitor the ground at the plug for a change in resistance. I see nothing in the circuit that makes me think that the ECM can vary the speed. Once the relay closes it should be all out? maybe it is a combination things. It could be like the old gassers that used a thermal type clutches where as the hotter the radiator gets the tighter the clutch gets. BTW mine is a 2005 2500 diesel 6 spd. Answers to the questions will help me fill in the blanks. Thanks

BigIron70

controlled by ECM but you can test fan clutch by grounding pin 1. Should lock fan clutch after a few minutes. Raise RPM up fan should increase also. Also check fuse 35, this fuse also powers the waste gate control. Usually sets code if fuse is blown. Pin 6 on fan clutch 12 volt, pin 5 is 5 volt reference voltage. Measure the resistance between the signal circuit in the fan clutch assembly and the return circuit in the fan clutch assembly. If less than 10 ohms replace fan clutch. Usually code P0483 Fan speed will set if you are having fan clutch issues.

anix

Thanks Big Iron this is the kind of info I need. Does the ECM JUST turn the fan off and on or can it control the speed? I have noticed that the fan turns slow when the engine is cold but as it warms up it will speed up some but I have never heard it lock up even with the ac on. I read last night where the high pressure switch on the ac line should turn the fan on around 240 - 270 psi so if grounding pin one will turn the fan on I will replace the transducer to be on the safe side as mine has already vented the freon off once and I thought it was the front seal and replaced everything under the hood (was warranted from the last owner) and I had rather not let the pressure get that high again. Thanks I will post my results.

BigIron70

It controls the speed and varies amount of clutch engagement according to engine temp and A/C high side pressure. Yes I have seen that problem many times with fan clutch not working and A/C pressures going well over 500 PSI and causing the burst disk to vent the Freon. I have also seen some people install a electric fan on the A/C condenser, really works well when in heavy traffic on those hot summer days here.

anix

Update....New OEM fan clutch solved the problem.