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HVAC Driver Air Blower Motor Circuit
I have a electrical gremlin I need help with.
The bus has driver AC (small system). Uses Tecumsch Compressor. I am blowing CB#79 if both blower motors are plugged in within ten seconds.
Here is some history. Just picked bus up from purchase in Eugene and drove all the way from Eugene Oregon to New Braunfels with no problems.
I had the AC system fixed when at TEC Equipment and the technician tested it and said it worked great. I also had a LED headlight mod done after the AC was fixed.
When I picked bus up last week we had a issue with CB 79 blowing after 10 seconds of both blower motors running. So I started isolating problem by unplugging one motor and/or the other. The system runs flawlessly cold air or mixed air. Ran this way all the way back to New Braunfels Texas with PAX side motor unplugged.
Before I left Oregon I had the chassis tech check the amperage on each motor. RH side pull 5.5 amps and left side pulled 4.5 AMPS. When I check the circuit breaker #79 per schematic in front junction box area I found it was a 15 AMP breaker in a 10 AMP slot which tells me someone was trying to resolve the issue the wrong way. So I replaced with factory correct 10 AMP breaker.
I then looked at Relay #33 and swapped with similar relay #60 and got same results. Since I had a headlight mod done I have also pulled all CB for breakers to isolate them from problem and still have same issue. I have new relay coming in thinking it may be weak legs.
Need some help with diagnosis what am I missing. Attached are diagrams.
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5 Replies
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Ed,
What about fan speed, does that have any impact on the failure? I assume the higher the speed the higher the amp load.
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Tom,
I thought about that as well. When you turned the as came with bus original fan speed rheostat on it only had one speed – high (on/off). So I replaced that rheostat and the temp rheostat as a package together and what I found was there is no variance in motor speed…which does not sound right. There should be some type of speed control in the Rheostat (0-10 voltage) something. Comments?????
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So the gremlin was the following. Drivers side motor is pulling 4.25 AMPS and passenger side motor was pulling 21 to 22 AMPS. The whole system is only suppose to pull 11 AMPS. New motor on its way from Prevost online. It is a bear to get the PAX motor out of the passenger side took me two hours after connecting DC Clamp AMP gauge to wires to trouble shoot.
What lead me to the motors was the folks at Mobile Climate Control (MCC) the makers of the dash air system who gave me the attached drawing showing what the system should be pulling amperage wise. Glenn their field service rep said worn brushes would lead to higher AMP draw. Told me motors typically last 20000 HRS. Kevin in tech center got me the engineering answer I needed. This all happen in one day.
I found MCC was the the manufacturer of dash air by using a inspection mirror and reading the label on bottom side of motor.
Prevost does not post anything about this supplier in the supplier publications online other then parts in parts catalog.
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Good post Ed, glad you sorted it out.
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Here was the culprit. Water damage to PAX blower motor. The motor was full of water. No sign of water below on chassis floor below blower there is a drain in the floor just below motor. Just liquid in motor. Two possible reasons for liquid in motor; a. Water leak at Webasto heat line at one time squirting into motor, b. Leak from drain line that comes from some system above maybe front AC. Anyways motor was full of liquid. And it had to be shooting into motor to get through the case
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