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Dash Air Issue
Our Dash Air has been having some issues. Looking for some advice.
Our coach, a 2000 Marathon on a 1999 H3-45 shell has dash air, but no OTR air. After a problem with our dash air heat in 2016, Prevost Prevost installed a new dash air control unit as the original was updated. There was some re-wiring done by Prevost at the time since the dash air control has Driver and Passenger selections and we do not have over the road air. The system worked fine for several years.
In the Spring, we were not getting cold air from our dash air and I discovered the belt to the compressor was broken. The compressor had seized. TEC Coburg, OR replaced the compressor which immediately also seized and broke the new belt. Another new compressor was installed. The tech was unable to determine the problem. He did figure out a work around where I would have to remove a relay to shut the air conditioning off. They suggested I go back to Prevost as the system was no longer wired per the wiring diagrams. The tech also advised me not to use the dash air conditioning rocker switch. When the dash air conditioning was operating, the cooling fan was on high.
I took the coach next door to Marathon and they agreed to try and work out the issue. The tech was able to rewire several things back to the original wiring scheme, he installed a switch in the left rear electronics compartment to turn the air conditioning on and off. He advised me not to use the air conditioning rocker switch on the dash as he was not sure what would happen.
After driving the coach, we stopped and turned on the new air conditioning switch in the left rear electronics bay with the coach running. The engine cooling fan did not go to high speed. We drove a little further and I was concerned about the engine cooling fan not going to high so I stopped and turned the bay switch off. Interestingly, after turning the new switch OFF, we were getting very cold air from the dash air controller set to 64 degrees and outside temp was 78. It seemed like the dash air conditioning was operating.
What should the air conditioning rocker switch do in our coach? Should the engine cooling fan run on high when dash air conditioning is ON?
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3 Replies
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My bus air was cycling off and on, Prevost determined it was the controller. New controller was ordered and installed, it froze up the dash and caused the low PSI alarms to go off falsely. Turns out the NO bus air controller was installed in a Bus air unit causing the short. Prevost did stand behind their mistake and replaced the dash and installed the correct controller.
Chuck
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Your culprit maybe the Fan/Rheostat Control Box……this is a very rare part. Once you turn dash air rocker switch on you should have two switches nearby one that controls heat and cool and one that controls fan speed. If this box is bad you will have one speed and maybe no control. When mine went bad i kept the old core. I found this box…my bus not yours… forward of the PAX Entry door behind the Marathon installed Deco Panel. You can find this part in Prevost parts online diagrams and in your wiring diagrams. If Prevost rewired your dash air I would ask them for the wiring diagram without it …. no help……
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Thanks for the replies. Our heat/air conditioning controller has a driver side and a passenger side with a window to select temp and a switch to select air conditioning/heat/defrost fan speed along with a recirc switch and selections on how to distribute air – all on the controller unit. We do not have OTR air so the “passenger” side of this unit has no power and is inop.
Separately there is a rocker switch for heat and another for air conditioning. We do not have a separate rotary switch to control air conditioning/heat/defrost fan speed. I think the “Heat” rocker switch allows the water valve in the front of the coach to open. I’m not exactly sure what the “air conditioning” switch does. Does it engage/disengage the clutch for the air conditioning compressor? What in the air conditioning system causes the engine cooling fan to go to high speed?
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