Dear Dave,
The Coleman-Mach 45054-8792 A/C–heat pump on my 2020 Winnebago Navion 24V stopped working. I used my multimeter to check the compressor and the three capacitors and all appeared to be working correctly. I suspected the thermostat, but it still operated the furnace. So, reading your article on checking the thermostat voltage in today’s RV Travel newsletter, I checked it with the multimeter. It also works perfectly.
Using your advice to check the control panel, I removed the return air cover plate, opened the metal box, and found the 120vac wiring insulation on the terminal block melted and the white wire burned in half. See the attached photos.
Obviously, the 120v power shorted out, but why didn’t the circuit breaker blow before it could get that hot? I don’t want to reconnect the wiring if there is still a problem that caused the short. It looks like a fire source waiting to happen. Do you have any ideas? —Steve, 2020 Winnebago Navion 24V
High-amp draw situation?
I received this question and photos and initially thought it looked similar to a high-amp draw situation that I have seen many times. Here was my initial response:
Dear Steve,
It looks to be high-amp draw, which is common at startup, sometimes as high as 45 amps, that happens so quickly the breaker doesn’t trip. I sent your question to my Coleman (Airxcel) contact for suggestions. However, I would start with the return filter to make sure it is not clogged and maybe adding a SoftStartRV? What really needs to be done is an amp-draw test after you install new wiring. Let’s see what my contact suggests.
I got this back from Steve:
Thanks for the incredibly quick response, Dave!
I worked with an Airxcel tech years ago to troubleshoot a problem with the A/C on a travel trailer. Using photos of my system and a bunch of emails, we were able to find the cause and fix it. He even sent me the part I needed. But it was minor compared to this one.
I clean the filters before each warm-weather trip and regularly when we are on the road for an extended period. They are clean now because I also checked them. But the heat function of the heat pump has never worked since we bought the RV when it was a year old and had 11,000 miles.
I think my A/C breaker is only 30A. So, a 45A draw, even if instantaneous, is a huge concern, especially when I realize how close we came to a real meltdown. If that excessive draw is possible, why doesn’t every unit already have a soft-start system installed? —Steve
Here is what I got back from Airxcel:
The damage here was not due to a short, which is why it didn’t trip the breaker. This was a wire that was not completely secured in the connecting lug (screw likely not tightened completely during installation). When you have a loose connection on an electrical circuit, the flow of voltage through that connection heats up the wire, which will cause it to corrode. The corrosion as it increases will cause an even worse connection, and eventually you see the wire burn out (as in this case). There is likely nothing wrong with the unit or the box (aside from the damage to the 110VAC connecting lugs).
After reading this, it makes sense. A prolonged high-amp draw that could cause this type of damage would eventually trip the breaker. I also agree that A/C units should have a soft start installed. However, when I asked both Dometic and Airxcel, they indicated the roof A/C market is so price-competitive that even the slightest increase would mean lost market share since nobody has the feature. It isn’t even on residential units originally. Since Thor bought Airxcel, it will be interesting to see if the product will be only available on Thor products and if the a soft start feature will be incorporated.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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We had a “soft-start” installed on our AC for a totally different reason but now I’m glad we did, for this reason.
Shorts blow fuses or circuit breakers. I could see immediately that it was a loose connection. Your circuit breaker will trip as it’s supposed to but it hasn’t gotten to trip amperage. Think of a Bath heater, it gets red hot without tripping the breaker. It’s supposed to.
ideally it would be advised to go thru the whole rv and tighten every screw and bolt in your mobile earthquake.
Thank you, Dave! 🙂 Interesting scenario. Thank you for forwarding the tech’s response! 🙂 Safe travels! 🙂
I was in the HVAC industry for 12 years during the 80s. As a service, we would perform preventative maintenance on AC and refrigeration equipment each spring, which did actually reduce the number of compressor failures over the summer. One of the first things we always did was to go over every electrical connection to tighten them. Amazing how many we found were loose, but I believe that screws loosening is a “normal” part of their operation due to thermal expansion and contraction. They do need to be checked periodically!
Hey Dave that’s a wake up call for me! About 6 months ago I was exercising my generator & when I tried to run my AC’s nothing happened, that never happened before. I ran a diagnostic check & it said no power, hmmm my microwave was working along with my refer! It took me a while to wake up & check the breakers & sure enough both were tripped. I don’t have a clue why. But after reading your reply to Steve I’ll be checking those connections on my AC units.
Thanks for the great information
Snoopy
Thanks for all your help, Dave! And for sharing my problem with others. Hopefully, this article will keep a few RVers from going through the same scenario. And sell a lot of Soft Starts! 😁
Wow! Thanks Dave and Steve too! This is a reminder to me to check some other connections like the batt. hot lead to the couch solenoid (found loose once), and the transfer switch connectors! So glad you found the problem before the disaster and sent the pics for us to review. Fire is my biggest RV fear! Thanks again.