AC upgrade

[DaveBizzy]

Hi All, I am new here and of course everyone joins forums once they need help LOL! We have owned our 2005 Tradition 40J since 2009 and added 100K miles to it over the years. I have decent mechanical and electrical skills and know about 90% of the mechanics and systems on my coach. We have done numerous re-fits and upgrades over the years. Hopefully some of you have done what I am getting ready to do. It's time for the dreaded AC upgrade to Mach 8's since they have heat pumps and condensation pumps. I have had the parts delivered but I'm concerned about compatibility.
Old units 9023C879
Atwood thermostat
I have hydrohot
New units Mach 8's 37024-079
New Control boxes 9630A751
New Thermostat Micro-Air EasyTouch RV 345

So here are my concerns:
1. Is there sufficient wiring in place to connect everything?
2. Is the Hydro hot controlled through the control boxes or directly from the thermostat?
3. Do I have the right components for what I'm trying to achieve?

If anyone can shed some light and has been down this road thanks in advance and I'm happy to pay it forward!

 

[allenlook]

Everything above the roof is "dumb guts", except for the control box, that is the real brains of the AC unit.

It needs to be able to speak with your thermostat to set the mode (heat / cool / fan) and to turn the unit on and off based on the thermostat's commands (fan speed, AC mode, HP mode).

As such, It also needs to match your unit so it's not calling for a fan speed that doesn't exist or the heat pump (reversing valve) or resistive element when you don't have one.

So, you need a control box that can talk to your thermostat, think of them as a couple, and you need a control box that can manage all the modes of your AC/HP unit.

An additional wrinkle is that you need daisy-chained multi-zone control, either 2 or 3 AC zones depending on your coach, and furnace/hydronic control. Check with MicroAir or look at your thermostat to see what plug it takes and how many wires it needs (as many or fewer wires you're good to go), but you'll have to re-crimp the ends or use an adapter (my preferred choice) if the new differs from the old. If you re-crimp, pay attention to the orientation on each end of the cable, there are two ways to crimp an RJ plug onto a cable, straight through and reversed.

Dometic AC setups sometimes control the furnace from the AC unit, and use the AC as a "mixer" for thermal distribution. Coleman more commonly controls the furnace directly from the thermostat with a 12V switched signal. The Atwood calls for two 22-ga. wires from the hydronics to each zone control board, but I haven't torn into it to see if that's really required or what is really wired up.

One last consideration is that heat pumps and AC units often have different opening configurations in the roof, the Atwood install manual shows the difference between Dometics, RVPs (Colemans) and others of that vintage. You should be prepared to rejigger the opening configuration as needed with foam board, tape, and weatherseal. They all use a 14" square hole, but the intake / output is very different depending on the unit, ducted vs. unducted, etc.

On these coaches and in this age range anything is possible.

 

[allenlook]

Here is the Atwood ACCS manual for your reference. It shows the orientation to crimp the RJ connectors if you go that route, it outlines the furnace connection(s) (you may have one or more zones hooked up, and the thermostat will likely show "FURNACE" for those zones only, and it shows the roof opening configurations for the AC/HP units of that era.

 

[DaveBizzy]

Everything above the roof is "dumb guts", except for the control box, that is the real brains of the AC unit.

It needs to be able to speak with your thermostat to set the mode (heat / cool / fan) and to turn the unit on and off based on the thermostat's commands (fan speed, AC mode, HP mode).

As such, It also needs to match your unit so it's not calling for a fan speed that doesn't exist or the heat pump (reversing valve) or resistive element when you don't have one.

So, you need a control box that can talk to your thermostat, think of them as a couple, and you need a control box that can manage all the modes of your AC/HP unit.

An additional wrinkle is that you need daisy-chained multi-zone control, either 2 or 3 AC zones depending on your coach, and furnace/hydronic control. Check with MicroAir or look at your thermostat to see what plug it takes and how many wires it needs (as many or fewer wires you're good to go), but you'll have to re-crimp the ends or use an adapter (my preferred choice) if the new differs from the old. If you re-crimp, pay attention to the orientation on each end of the cable, there are two ways to crimp an RJ plug onto a cable, straight through and reversed.

Dometic AC setups sometimes control the furnace from the AC unit, and use the AC as a "mixer" for thermal distribution. Coleman more commonly controls the furnace directly from the thermostat with a 12V switched signal. The Atwood calls for two 22-ga. wires from the hydronics to each zone control board, but I haven't torn into it to see if that's really required or what is really wired up.

One last consideration is that heat pumps and AC units often have different opening configurations in the roof, the Atwood install manual shows the difference between Dometics, RVPs (Colemans) and others of that vintage. You should be prepared to rejigger the opening configuration as needed with foam board, tape, and weatherseal. They all use a 14" square hole, but the intake / output is very different depending on the unit, ducted vs. unducted, etc.

On these coaches and in this age range anything is possible.

Good morning Alan-thanks for the reply! Fortunately my existing units on the coach were Mach with Atwood control boxes and thermostat. I'm currently in the cross-referencing the existing system to work with new dometic control boxes and a micro air compatible thermostat. The Mach 8's I am adding are legacy compatible with previous versions. It looks like it's going to be fairly straightforward with a few nuances such as replacing temperature sensors, changing RJ-45 for RJ-11, and changing connectors to the correct pin configuration. Worst case is that I burn something up or have to switch the system back to the atwood control boxes and thermostat which is still fully functional but archaic. I'm actually looking forward to the project. The hardest part is been sifting through a lot of an accurate information from a lot of different sources.

 

[allenlook]

Glad to hear you're on the journey - be really careful you don't burn out one of the *old* control boards. I did that on a customer's rig once and ended up sourcing a replacement off eBay and driving 6 hours for free to make it right. Had to reboot his MicroAir several times to get it to recognize the system. Never did that again!

 

[DaveBizzy]

Glad to hear you're on the journey - be really careful you don't burn out one of the *old* control boards. I did that on a customer's rig once and ended up sourcing a replacement off eBay and driving 6 hours for free to make it right. Had to reboot his MicroAir several times to get it to recognize the system. Never did that again!

If everything goes as planned my old Atwood boxes and thermostat will be on eBay in a couple weeks since these components are so hard-to-find! BTW I reached out to Backwater a few times with no response as well.