Malewis11

Hello, I have attached some interesting information for the SD assembly regarding the output voltage and operational theory. It seems to confirm that the SD is looking for a PWM signal at a duty cycle from the ECM that is proportional to the engine cooling needs therefore the fan speed requirements. The SD is capable of additional thermistor and aux inputs but mine is limited to one ECM input. For me this is boiling down to what the actual function of the SD electronic module is. It appears that our rigs are not utilizing or needing the full functionality or multiple inputs of the SD electronic module. It probably does not use the ECM signal/voltage to drive the valve but Bill’s setup appears to show that it is capable of doing so. The SD’s is programmable, so it likely has the ability to adjust output based on aux inputs (overrides) as well as keep the fan running even when the ECM provides 12 volts, which is precisely what the aftermarket dc motor controller does. What ECM voltage says go WAO? This is possibly 0 or a variable loaded into the SD by Monaco long ago based on engine temps. Personally, I’d rather go WAO at 7 volt than overheat. I’d recommend as much electrical isolation for the ECM as possible. If this is in fact accurate, there has been a lot of wasted money and time rebuilding and buying new SD controllers. Mark L

Hi All First I can report that after cleaning the connector contacts and replacing the Hirschmann plug my fan ran a lot slower at startup. Not sure of the speed but it wasn’t roaring like usual. We will have to see if it speeds up at high temps but had to cancel my short trip because of an issue with my brand new tow bar. Im not an electrical engineer but my understanding of the PWM is that it doesn’t modulate the outgoing voltage but switches the power on and off known as the duty cycle. It lowers the average voltage thereby reducing motor speed. 12 volts at 50% duty cycle would mimic 6 volts. It stands to reason that if the supply voltage dropped to 8 volts the output would be mimic 4 volts if the PWM setting didn’t change although I not sure if it’s linear. You can measure the output voltage but it has to be tested under load otherwise you will not see the voltage drop. This is based on motors so how valves like ours react may be different but based on other’s experience it obviously has some effect. Since I didn’t install the PWM I’m planing on setting up an experiment to vary voltage and load to see what happens. I’ll report any thing I learn. Mark L

Hi Bob There is a Phillips screw in the center of the plug that connects to the valve body. If you remove that screw, the plug should come off easily. That’s when I discovered there was a lot of corrosion on the plug. Use a small screwdriver to pry off the plate on the connector to expose the terminals. My wires were almost completely disintegrated, but it was easy to determine which terminals the two wires were connected to. One was connected to the ground and the other one to the number one terminal. The other two looked brand new. The plug is exposed to moisture and is not water tight. Mine was oriented so that any water that entered the plug would be trapped. I rotated the plate 90° so that the wire entrance would point down. I do not plan to seal the wire entry so that if any moisture enters the plug it will be able to drain out, hopefully. Below is the plug that I purchased from Amazon. Best of Luck Mark

Hi Bob, I have attached information for the connector on my 2006 Windsor. As I was working to switch the fan control to the dc motor controller it was obvious that the connector was in pretty bad shape. The bigger issue was the Hirschmann plug on the solenoid. It was so corroded inside that there was no power getting to the valve. I picked up a new one for a few bucks and replaced it. I then verified that I had 12 volt power on both the 12v supply to the SD and from the ECM to the SD. I also now have 12v getting to the solenoid so my SD may be working properly now. Haven’t run the engine to confirm but will this weekend. I plan to make a harness so I can easily switch to the motor controller if I need to while hoping that the valve is good. I haven’t seen many reports of the valves failing, it’s usually the electronics. I haven’t delved into the thermal switch yet but putting a normally closed switch in would act as a fail safe breaking the circuit and sending 0v to MC at high temp. This would put the fan on high. Mark

Hi All, I certainly learned a lot from this thread and I’m hopping it will help me correct my fan issue. @Bill R I like that solution. Could you enlighten me on the installation and location of the thermal valve on our Coach? Also, with two years of testing under your belt is there a specific DC motor controller you would recommend? I think I saw somewhere else you said around 9 volts gave you the desired 600 RPM at cold startup, correct?