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Dash Air HVAC Control Panel Replacement
I went to Prevost in Richmond, BC, for service in the Spring. The dash a/c and heat were not working very well – not very hot and not very cold. My coach originally had OTR air, which was removed, and Cruise Air units were installed using the OTR air ducting.
At the time of my Spring visit to Prevost, it was determined the coolant was not circulating as it should. The tech rebuilt the water valve in the front of the coach and he also flushed the coolant system and replaced the filter and found a stuck valve in the engine compartment. A valve that allows heat in the front of the coach was not opening properly – it did not respond to control signals from the HVAC dash control – and Prevost recommended replacing the dash HVAC control unit with an upgraded version. I had read in PC that another H3 (with OTR air) owner, Al, had replaced his own dash HVAC control with an updated unit so it sounded logical that it could be the problem.
I returned to Prevost last week on Monday to get the new dash HVAC control unit installed along with some other service. The HVAC upgrade didn’t go so well. Apparently, when the tech installed the unit, nothing worked. We had to leave the coach with Prevost until things could be worked out.
The coach was with Prevost all week and some re-wiring had to be done. The wiring to the HVAC dash unit did not match the Prevost wiring diagrams. Prevost contacted Marathon for help, and at first, Marathon said the modification must have been done by someone else. Also Marathon does not share it’s wiring diagrams.
On Friday, with my coach still in the shop, I started casting about to see if I could find some help. I spoke with Marathon in Coburg, Marathon in Florida, and Prevost in Nashville along with another owner, Al, who put his HVAC dash control panel upgrade on PC. Prevost in BC was able to complete the HVAC upgrade on Friday.
When I picked up the coach on Monday, the HVAC Dash unit now puts out much colder and much warmer air. It does not work exactly as designed however (since the OTR air is not installed). To get A/C, you cannot use the Passenger side of the control at all. And the driver side of the unit controls the temp on the driver side when using heat, although the Passenger side can be turned on for additional heat.
I do not know how many coaches are like mine, or if mine is the only one like this. I believe Marathon removed the OTR and should have the wiring diagram showing how the dash unit installation was done. My logic for having Prevost do this work was that dash air issues sounded like something that related to the chassis. I would recommend that if you have a Marathon similar to mine, I would have the HVAC upgrade done by Marathon to avoid a lengthy installation.
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4 Replies
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Tad,
So do I understand that your Cruiseairs are ducted through the original OTR window ducts and you now have dash air instead of the OTR? Who did this conversion in the past?
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Hi Tom – yes I have dash air. I’m not positive about who made the modification but my understanding at this point is that Marathon removed the OTR air and ducted the Cruiseair units through the OTR ducting. The coach plan from Marathon shows the (2) Cruiseair units in bay 4, driver’s side. That would lead me to believe Marathon removed the OTR during the original conversion if that is where the OTR equipment is normally installed. Do you know of any other coaches set up this way?
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Tad,
Last winter, I had issues with my dash air not staying on. I talked with Al and thought I needed to change out my dash air control unit.
However, I was at Marathon in FL doing some other work and mentioned it to Marathon (although it’s a Prevost part). Marathon told me they had an upgrade for the dash air control unit which basically relocated the thermostat from behind the dash to under the dash. I’ve not had any issues since. Saved me $1,000 from installing a new unit.
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Here is Prevost up grade which comes with dash control box.
Comes from dash air exchanger control box passenger side to mounting above drivers right leg.
These is probably the OEM sensor Marathon went looking for behind dash, note small size.
When Tad phoned me I became very interested in his conversation about using the OVR bus A/C duct work with cruise airs. Apparently someone or Marathon did it on his bus which when you think about it was very clever.
Glad to hear Prevost got this repaired for you. Thanks for the post.
AL
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