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How to maintain and troubleshoot RV cooling systems


July 29, 2020

One impact of the COVID-19 pandemic has been an increase in RV and camper sales as travelers seek ways to get away safely and responsibly.

While they’re a great way to enjoy the outdoors and see America while practicing social distancing, the fun can be done in a hurry if a motorhome’s fan or fan drive is on the fritz. Whether you’re a mechanically-inclined owner or seeing increased RV traffic in your service bay, here’s everything you need to know about keeping things cool under the hood.

Naturally, summer is when most motorhomes obtain the most mileage – even when there’s not a global health crisis impacting people’s travel plans. It’s also the time when an engine’s temperature regulation is most at risk, either because of high temperatures or mechanical failures.

Motorhome preventive maintenance

Of course, regular preventive maintenance can reduce this risk. Here are some basics steps you can take on an annual or semi-annual schedule to stop problems before they occur:

1. Perform a visual check of the engine’s radiator, coolant hoses, expansion tank, water pump, AC system, belt, belt tensioner and thermostat. Look for signs of corrosion, wear or other defects.

2. Check the fan, keeping an eye out for defects, chips or contamination buildup.

3. If the fan clutch is air-operated (more on that in a minute), check the air line to the solenoid valve, air line to the fan clutch and the electric circuit to the solenoid valve.

4. Examine the fan clutch for any defects and consider a replacement or repair kit, depending on the issue.

Different types of fan drives for motorhomes

Built on chassis similar to semi-trucks, most RVs feature either an air-operated (pneumatic) or viscous-driven fan clutch, or fan drive. This component controls how fast the fan turns, and when.

Pneumatic drives come in on/off and two-speed versions; the latter provides more optimized cooling depending on the type of vehicle they’re in. Viscous drives are either on/off or fully-variable; they react to cooling needs in real time and allow the engine to spend more energy powering the vehicle and less turning the fan when it’s not necessary.

When a pneumatic fan clutch fails, it’s likely one of three symptoms is present:

  • The clutch won’t engage.
  • The fan clutch won’t disengage.
  • There is an air leak in the fan drive.

Viscous drives tend to have the first two issues. Due to their control by the engine computer, they don’t experience air leaks. But programming issues with controls are a third area of concern for these types of variable-speed drives.

So, what do you do?

We lay out the steps for diagnosing and fixing problems below. For more, fill out the form below to access a full troubleshooting guide featuring flowcharts for on/off, two-speed and viscous drives.

For an on/off or two-speed pneumatic fan drive that won’t engage, first check to see if vehicle air pressure is present. If it is, check the air and control system. If those aren’t working, you’ll need to repair it with the appropriate fan drive repair kit.

Horton has a detailed overview of these testing procedures you can refer to.

If the drive is an on/off or two-speed and won’t disengage, perform the same air pressure test to start. If there isn’t air pressure, you’ll need to do the same air and control system check and drive repair as above.

If there is air pressure present, your drive might be OK for the time being. To check, apply and release air pressure then see if you have any piston movement. If the pistons won’t budge, you need to repair or replace the drive. If the pistons do move, apply 90-110 PSI and try to rotate the fan by hand.

If the fan rotates freely, the drive is functioning as it should. If the fan doesn’t, it’s time for a repair or replacement.

A full listing of fan clutch repair and replacement options is available via Horton’s online catalog.

What about an electronically controlled, viscous fan drive?

In general, Horton’s field service team sees fewer issues with this newer technology. Unlike pneumatic fan drives, all viscous type fan drives have to rotate with the engine running to transition from engagement to disengagement or vice versa.

Electronically controlled viscous fan drives have a zero-voltage “Fail Safe” design. When there is any type of electrical issue (zero-voltage), an electronically-controlled viscous fan drive will default to full “on” mode. This keeps the engine from overheating until the vehicle can be repaired. Electronically-controlled viscous drives are engaged with zero voltage and disengaged when voltage is applied.

But if the fan drive won’t disengage (voltage will be present when no engine cooling is required), you’ll need to check if there’s voltage present at the drive. If there is not, there’s likely an issue with vehicle’s fan control system.

Assuming there are no issues with the fan drive itself, inspecting and repairing the engine’s cooling control system should take care of the issue.

If voltage is present, check continuity and Ohm resistance at the fan drive. If that reading isn’t between 6 and 14 Ohms, the fan drive or anti-rotation bracket needs to be swapped out for a new one.

And for a viscous drive that won’t engage, start again by checking the voltage. If voltage is not present (and the fan drive will not engage), the fan drive will need to be replaced.

You can also check engagement by simply disconnecting the fan drive from the engine harness. The fan drive should engage within 3-5 minutes. Also check for any fluid leakage in and around the fan drive; if leakage is present, the fan drive will also need to be replaced.

This article didn’t solve my problem

Most fan drives are designed specifically for certain vehicles, so issues and how to tackle them can vary. If you need some personal assistance, feel free to contact us directly and a Horton engine cooling expert will walk through the problem with you and help come up with a solution.