Blower motor not working on level 4

[Cpitt32]

Hey Guys... Looking for a little help... I have a 20114 Mack Pinnacle CXU613 and the fan motor stopped working on level 4... I thought it was the resistor and I swapped that out but it is still not working... Not sure what I should check next... If anyone has any ideas I'd appreciate the help...  Thanks in advance...

 

CURTIS 

[Mackpro]

The lower fan speeds go through the resistor. High is usually direct straight from the switch. Usually the back of the switch is melted. This is usually because the cabin air filter is clogged/dirty and the blower motor is trying to pull air through the dirty cabin air filter and it over heats the wires, switch  and connector on the HVAC control panel.  The cabin air filter needs to be changed at least every year. If it’s a farm truck or used in dusty  environment then every 3 to 6 months. The older trucks came with a blue mesh screen filter that you could wash out. It’s now been replaced with a fabric house style filter that you just throw away. Super easy to change except on the older CXU, CHU and GU trucks. A little harder to change on the AN, PI and GR trucks due to kick panel redesign. Also alway run in recirculating  mode keeps from drawing in dust and other stuff that clogs the filter . 

[The Heinz]

Mackpro is right on it. Usually that issue is caused by a faulty controller. Replace the cabin air filter and inspect/replace the control switch, and you should be fine assuming the blower motor itself is fine. 

[Timk]

Hey guys. So my ac/heat stopped working. I’ve replaced the blower, the resistor, the control panel and the relay. Still nothing. Will a dirty cabin filter keep it from working?

2016 Mack cxu daycab.

Edited July 22 by Timk

[Nickdieselz]

It sounds like you're on the right track by replacing the blower motor resistor, but since it didn’t resolve the issue, here are a few other components to check:

1. Blower Motor: The motor itself could be failing. Even though it may work on other speeds, the highest speed (level 4) often bypasses the resistor and runs directly through the motor. If the motor is faulty, it might struggle to handle the higher current load needed at level 4.

2. Blower Motor Relay: On some vehicles, the highest fan speed uses a separate relay to bypass the resistor. If this relay is faulty, it could prevent the fan from running on the highest setting. Check your fuse box or wiring diagram for the location of the relay.

3. Wiring and Connections: Inspect the wiring and connectors to the blower motor and resistor. A loose or corroded connection might only affect the fan at higher speeds due to the increased current.

4. Blower Control Switch: The HVAC control switch that changes fan speeds could also be the culprit. If the switch isn't working correctly, it may not be sending power to the blower motor on the highest setting.

Here's a quick way to diagnose:

- Test the blower motor directly by supplying 12V to the motor to see if it runs at full speed. If it works, the problem could lie in the relay, switch, or wiring.
- Use a multimeter to check for voltage at the blower motor on the highest speed. If no voltage is present, trace it back to the relay and switch.

Let me know how the testing goes, and I can help with further steps!