[jdkskyking]

Tuesday September 27, 2022

Recently while vacationing in Breckenridge Colorado at Tiger Run RV Resort…

I decided to add a circuit to manually send the cooling fan to max speed. 

My wife Kristi was thrilled by my mechchanicalvacation skills. 

As mentioned before, in the normal mode, the Engine ECM applies/sends 12v DC to a relay (in the right engine bay electrical cabinet) that is wired to the cooling fan solenoid mounted in the hydraulic manifold block. 

At coolant temperature of 217° the Engine ECM removes the 12 v DC to the relay which in turn removes 12v DC to the solenoid and sends the cooling fan to max speed. When the coolant temperature is reduced to nothing temperatures the ECM will apply 12v DC again a fan speed returns to normal.

   

   

I identified three spare wires in the right side engine bay electrical cabinet that ran up to the forward electrical area in front of the passenger seat. I eventually used two of the three wires to control a new relay and a indicator light when I manually put cooling fan in max speed. 

   

My initial idea was to add a new five pin relay to manually interrupt the ECM 12v DC signal to the fan relay and turn on a indicator light at the driver’s position. I wired everything to fail such that original configuration will not be impacted. 

I mounted the relay in the right side engine bay electrical cabinet and ran the ECM wire through the new relay and on to the original fan relay. 
I used one of the spare wires (blue/red) to provide the ground to the new relay from a spare switch in the left driver’s control panel. The switch provides the ground to the new relay. 

   

I used the second spare wire (blue/black) to turn on a LED light at the driver’s position when the relay interrupts the ECM 12v DC signal. The LED power is provided by the new relay. 

This is temporary, I’ve order a 8mm indicator. 
   

So why did I do all this work?
I want to have full control of the hydraulic motor that drives the cooling fan. If I see the coolant temp trending towards a temperature above 212° I can send fan to max early so the coolant temperature reverses the upward trend. 

Keep on mind, on my coach, the coolant fan’s RPM is dependent on the position of a plunger associated with the solenoid in the hydraulic manifold block. In “normal” mode (electromagnet energized) the cooling fan is rotating approximately half of the engine RPM. 600/300, 1000/500, 1500/750 etc. I checked these ratios with a photo tachometer, variation does exist. 
When the fan is “sent” to max by removing the solenoid’s 12v DC signal, the cooling fan rotates at a RPM that is close to the engine RPM, 600/600, 1000/1000, 1500/1500 and in theory, so on and so on…

When we left Breckenridge and headed east on I-70 I did my best to set myself up for success.
Engine driven A/C OFF.
Dash defroster set to hot with fan on high (rooftop ac on cold).
Limited transmission usage to 5th gear primarily using gear 3 & 4 on steep grades up and down. 
Used transmission PERF mode.
When able I tried to keep throttle position around 80%. 

I carefully monitored the coolant temp and when it exceeded 212° (coolant regulator/thermostat wide open) I placed the cooling fan in max and strived to maintain 1600-1800 engine RPM. 

Jumping through all these hoops kept the coolant temperature in a very comfortable range and it never approached temperatures that would possibly breach the CAT recommended maximum temp of 225°. 
A couple of times, I allowed the engine ECM to send fan to max to verify the system was functioning normally.

My future plan is to verify the hydraulic fan motor is functioning properly and investigate possibilities with improving radiator stack efficiency. 
I’ll also be installing an annunciator light for when engine ECM removes the 12v DC signal and another annunciator light when I manually send fan to max. 

Yes… I like switches and lights… and control! 

Take care,
JK