Pace Arrow: Pace Arrow Dometic AC

[Neicy]

Question is: Two (2) Roof Top AC's. Dometic 13,500 BTU Power Saver and
Dometic 11,000 BTU Power Saver.
Last Year we had to replace the front AC (13,500) and now the Rear (11,000) has gone out.
Can we replace the Rear 11,000 With a 13,500 Safely? There is less than
$100 Difference in the 2 Units. The Power Saver Feature Allows to Run
Both and They Fade as Necessary Due to Amp Usage.
Thanks!

[VIETVET72]

Check the circuit breakers for the front, 13,500, AC. If it's the same as the rear 11,000, you should be OK to go with a 13,500 in the rear. If the breakers are not the same, you'll need to check the wire size to see if they are the same. If the wire sizes are the same you would be safe to replace the rears breaker with what's used for the front AC unit. If the wire size is smaller for the rear AC, you wouldn't want to go with the 13,500 AC in the rear.

[MrMark52]

More often than not these rooftop A/C units quit due to issues with their internal electrical wiring and/or electrical components (PTC start device or start capacitor/relay).

My opinion is, an assessment by anyone other than a skilled HVAC technician will result in an incorrect determination of failure - as any of the failure issues described above are easily and economically corrected.

As for upsizing the new unit - typically the rear unit in a MoHo is smaller because it doesn’t see the heat load that the front unit see’s.
Oversizing an A/C unit is worse than undersizing because the unit cools the air quickly but doesn’t get a chance to remove enough moisture from the conditioned space - as a result, it will short cycle and decrease the comfort level in the space.

But agreed with VIETVET72 - verify the breaker and wire size (probably all OK - but while your at it, inspect all the internal connections inside of the breaker panel as they DO come loose in MoHo’s) if you decide to upsize.

[Neicy]

Thanks for the responses. I did fail to mention this is a 2004 Pace Arrow, therefore the Units are approximately 19-20 years old. We replaced the front AC last year. Due to the age of the unit last year, we did not have anyone assess it, just figured it was time.
I will have the wiring and fuses etc checked out, prior to making a decision as to the unit to order.
I thought at some point I had read on here that someone did just replace with
a 13,500. Totally not needed as the two of them will freeze you out, we usually only run one or the other.
Again Thanks

[MrMark52]

Call me cheap - but unless the compressor has been properly assessed and known to be bad, or there is an unrepairable refrigerant leak (like in the coils), then any of these units are worthwhile to retain.
Pretty much everything else is fixable.

Yes, efficiencies may not be what they once were, but you’ll never get payback against the cost and installation to a new unit.

[Jon_C]

Im hanging onto my 25 year old units as long as possible, they don’t build them like that anymore

[Neicy]

Thanks, I am going to have my AC guy take a look. Wish I had on the one I replaced.
2021 it was $789 including shipping, same unit now $1100 plus shipping
Like everything else

[MrMark52]

Originally Posted by Neicy

Thanks, I am going to have my AC guy take a look. Wish I had on the one I replaced.
2021 it was $789 including shipping, same unit now $1100 plus shipping
Like everything else

As I’ve mentioned on this and other boards - these units have a combination of conditions not encountered by your residential HVAC systems, to include -

1) Input voltage variations - especially the voltage lag that occurs when the thermostat first energizes the unit to start cooling. Decreased voltage increases current, increased current thru ANY resistance results in heat. Heat destroys crimped connections (which these rooftop units are full of).
2) to build units more economically, which results in reduced long term reliability, available parts are also marginally designed.

Compressors and fin/tube coils fit into a class of manufacture of a very narrow bandwidth.
The manufacture of electrical components and wiring class of manufacture is all over the place.
After 40+ years of working in the HVAC industry - 95% of A/C unit not working was due to electrical issues or electrical component failure, with a few condenser fan motors failures thrown in.

[Neicy]

Thanks! We were in Florida for January and it was working fine. Didn’t use it for couple days due to colder temperatures. Went to turn it on one day and it sounded weird and never heard compressor click in, just a weird hum, no blower. We cut it off and only used the other one. Our thought was due to age we would replace it but after comments on here I will make an appointment at the RV dealer we use and see what he says. Don’t want to pay him to install though, we did the other and was pretty easy
Thanks for everyone’s experience and comments!

[MrMark52]

Unless the RV service place has a good competent AC service tech, I would stay away from them. And at $1100 against hourly shop rates and vaguely competent techs - it tends to be cheaper/easier to just replace the unit.

Sadly, finding someone who doesn’t just want to change parts and/or hook his gauges up is hard to find.
The compressor not starting could be due to a burned wiring issue or failed start/run component. Which in turn the compressor trying to start could draw voltage down enough that fan/blower couldn’t get turning like it should which also pulls the voltage down even more..

[gt350ed]

Our motorhome is a 2000 Pace Arrow Vision. A little more than a year ago, we replaced both the front and rear with new units. We went with the 13,500 in the front and 11,500 in the back. Same as what the MH came with originally. For the various reasons cited here, we would recommend you do the same. We're out in Arizona and did business with a company in lake Havasu City. We paid a little over $1,800 for both units and paid $500 to their tech who wasn't independent contractor in the area. He had both units swapped out within about an hour. And because we didn't change anything regarding the units and their BTUs, everything was plug and play.