[BusNit]

I started removing the non working middle ac condenser today. I think it may need to be evacuated and recharged later in order to remove it to rebuild the unit underneath it. The wood shelf it sits on is fongoliated and delaminating too. I have a couple of Grainger 3RCX7 motors to be picked up later this week. New capacitors and a couple of new PTCR starters as well. My question is do I just order straight 2 terminal 20MFD compressor run capacitors if I will be using the capacitor that comes with the Dayton blower motor? My dometics use 20/7.5 capacitors and I am under the belief the 7.5 portion is for the existing blower motor. (Condenser fan) Any other tips? Compressor contacts under the cover look spotless. All units were blowing cold air before dying.

[Richard]

You are correct. The 20/7.5 MFD is for both the compressor and the fan motor. What size cap is supplied with the Grainger replacement. You could buy a 20/? MFD to simply and utilize existing wiring. ?being the Grainger supplied size. The black cap on the right is the START cap for the compressor, and the PTCR just above it is to take the start cap out of the circuit as soon as it starts up.

We discussed before, but personally I would replace the wire nuts with the Alumaconn connectors.

While you are in there, buy a fin comb and straighten the bent fins as well as you can to improve air flow.

Are you going to use a starter cap with a built in PTCR or utilize the setup that is there?

[BusNit]

I didn't think of finding out what the rating was on the Dayton motor so I ordered a straight 20MFD capacitor and the proper start cap with the 15k resistor. I decided to keep the thermistor in the circuit since it all worked for the last 30 years. hadn't thought about just removing all that junk and going with a new hard start cap. That's ok. I can dabble a little with a/c systems but not a true engineer with them. Of all the tools I own for HVAC, I do not have a recovery machine, tank or the capability to sweat silver solder. Perhaps If I did, maybe I could go a little further? (Recovery of R22 and disconnection of lines)

I do plan on straightening the fins as I have the tool and giving these units a really good wash down. They are full of dirt both Oregonian and Arizonian dirt! As for the alumiconn connections, I was just going to solder everything. Yes, I am the solder, make it permanent king! (Solder now, ask question later!) True believer in minimizing resistance and failure points.

[johnkosir]

As a retired HVAC contractor if the unit does not have a leak i would not remove the charge i would just carefully remove the unit with out kinking or breaking any lines fix what is broken and carefully put it back together

[BusNit]

I agree with you John, but I cannot get to the unit beneath it or replace the rotted wood shelf the top one sits on. I may just rebuild the top unit and lthe bedroom condenser as it is in a separate by by itself. the front unit will stay as is. I am so hellbent on not putting roof airs on if these fail. The one portable inverter unit is doing a phenomenal job of keeping the 2/3's of the coach cooled. Not sure how its going to handle the 115's when they come rolling around. Prefer to keep the load on the portable rather than continuously wear the basement units. Two of the three independent HVAC guys I called do not want to do the job stating they do not work on RV's even after showing them pictures of what's involved.

[Georgeb]

Ok nThe bottom unit will ALMOST come out
The guys at Newell use 2 wooden wedges 
And lift up the upper units plywood 

AND the lower unit just has enough room to
Come out

[bestgenman]

Simon,  I have a condensing unit and several other parts for the evaporators including one motor.   I don’t know the condition of the condensing unit.  Let me know if any of these parts could be useful.

Several C/U’s were rebuilt using rooftop frames, cut down, where the evaporator coil was removed and the condensing coil fitted into the old evaporator position.  The squirrel cage fan remained where it pulled cool air across the coil and downwards forcing it out underneath.  Cooling efficiency was greatly improved.

[Richard]

We all have different ways of looking at things. Building on your wish to keep the existing units, Gordon's input of repurposing other AC units, and my positive experience with the Dometic's ability to freeze you out without the usual AC noise, I think you may have to investigate the possibilities.

You said "Of all the tools I own for HVAC, I do not have a recovery machine, tank or the capability to sweat silver solder. Perhaps If I did, maybe I could go a little further? (Recovery of R22 and disconnection of lines)"

A recovery machine, a MAPP gas turbo torch, the recovery tank, a set of scales, and a tank of Nitrogen will set you back less than a thousand dollars. You have already experienced that is difficult to get anyone to look at the unit. Don't bother with an RV tech. You may want to think about equipping yourself to keep those units going. I am with John Kosir, if it breaking into the system is not 100% necessary, then don't. On the other hand, having the ability to work on them frees up a ton of options.

Part of the fun challenge is putting the noodle to work to keep those old girls up and running. You have already demonstrated your dedication to doing that, and you have also demonstrated that you have the technical skills to learn what you don't know about
AC systems. If a mule like me can learn it, then someone like you will ace it.

[BusNit]

Thanks for the encouragement guys! I think I am ok on parts. After a few hours of cross referencing numbers and through previous attempts made by others, I found what I needed and they are enroute.

I did think about future options of splitting a package type unit. As far as tools, I do have literally everything including the charge scale except the recovery machine tanks and acetylene torch. Can I get away with a Mapp torch? I have that at least... Love my fieldpiece HVAC tools. I self installed three mini splits where one needed a higher R410 charge due to increased line set length. I'm rusty at remembering sub cooling methods of charging.

[Richard]

Yes, a MAPP torch will sweat silver solder. I had to prove it too myself, cause I wondered if I could do it on the road.

You can watch the utube about soldering with silver. It is quite different than normal water pipe. Cutting to the chase scene, no flux, get it dull red, and let the solder stick touch the metal after the pipe is red.

If you get to that point, we can help with the superheat/supercool charge of the system. If I remember correctly, the Dometic uses a capillary tube and not a TXV,

Amazon sells a nifty little slide rule calculator thing that figures it our for you. https://www.amazon.com/HVAC-Superheat-Su...RydWU&th=1

Or if you are John, you have the cutest little sensors that screw onto the pressure taps, and send the info to an app on your phone, that does it all for you.