Operators are correct; certain Van Hool CX45 buses experience reduced air flow.
- JAMES MORRA
- Oct 14, 2024
- 3 min read
What's Going On?
So, I was working with some of my current customers, teaching their technicians how to service the HVAC system on their Van Hool CX45 coaches, and we noticed that the airflow for the passengers is weak on the model year 2020 and newer vehicles. This was a problem that came up a while back, along with some issues with the heating controls being set incorrectly. Van Hool had fixed those initial concerns quickly once they were discovered, but it seems like the slow fan speed is still an ongoing problem.
How Does it Work?
If you're reading this, you might be wondering what I'm going on about and why the fan speed is sluggish, right? Well, let's quickly dive into how the passenger fans are controlled on the newer model year 2020 CX45. If you look at the diagram below, you'll see three motors on each side of the coach in the parcel rack (bottom left and right of the diagram). The white wire coming from Node.4 E13 sends a Pulse Width Modulated (PWM) signal that adjusts the fan motors' speed. The program in the coach sets these values, and they can't be changed unless the factory program is altered.
What Does the Dash Say?
You can check the fan speed using the digital dash, as shown below. When the AC is on and the coach's interior temperature is a bit warmer than the set point, the passenger fans should be running at full speed. The image might show "Heating," but that's also an old glitch that was not fixed. Full AC mode equals 100 percent fan speed (check out my article on how HVAC systems should work).
Now, if we trust the screen above, everything seems fine, right? But let's double-check the PWM signal from that white wire to see if it's at 100 percent. An oscilloscope gives a clear picture of this pulsing signal, showing that it's high (24V) for only 70 percent of the time.
How Does This Affect Operation?
Knowing that the fan speed isn't at 100 percent due to programming, let's see how it affects airflow. Before adjusting the signal to 100 percent, the airflow measured at the inlet of the passenger air handler was 3.35 meters/second.
After setting the signal to a true 100 percent, the airflow increased to 5.44 meters/second, a nearly 65% boost that was not only measured but also felt and heard.
To give you an idea of the cooling performance, the test coach had its interior temperature set to 62F (screen shows 68F, but that is also a display glitch), starting at 79F (exterior was 83.6F), and it took about 1.5 hours to drop to 63F!
A second coach with the test controller started at over 100F and dropped to 82F in just 30 minutes. This is with an exterior temperature of nearly 89F, and fresh air flaps open during test.
Why is This Happening?
I'm sure there are reasons for reducing the fan speed, but in places like Florida or Arizona where temperatures often hit triple digits, having maximum cooling capacity until you're close to the setpoint just makes sense. Keep in mind that this will also affect how quickly the coach heats up, but the problem should not be as noticeably because there is also supplemental heat from the floor radiators to help. The current feedback from the one operator that utilizes this coach regularly was that he had to turn up the temperature because it was getting too cold for the passengers with it set to the minimum as they typically set the system. Before the update it was likely that the interior temperature would not reach the setpoint so operators would just turn it all the way down. Now that it can reach 62F it is necessary to set it to 72-76F like it should be.
The Fix
So, I engineered a circuit to fix this issue. It converts the incoming PWM signal to make sure that the 70 percent signal is adjusted up to 100 percent (to reflect what the dashboard shows). As the fans slow down, the circuit adjusts accordingly. I've also added a bypass switch in case you want to go back to the original fan speeds. Right now, there are 5 prototype circuit boards in the works. Once they're good to go, I'll start taking pre-orders. If you're interested, hit me up! And don't forget to sign up for updates on this and other solutions I'm working on.
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