2019 Minnie Drop 170S A/C Trips Breaker After Running

[B2bear]

I just bought a 2019 MD170S that has not been used for the last 4 years. We tested the AC while inspecting prior to purchasing. It was on around 40 minutes. When we got it home we put it on Shore power. The AC would run only 30 to 60 minutes and then pop the breaker. At first I thought it was due to running it on low and could be freezing up since it was nice and Cold. So I tried it on High but lower on temp (it doesn't have a real thermostat to set temp). Still would only run 30 to 40 minutes, sometimes as short at 10 minutes before tripping the trailer breaker.
I came to believe that it was a weak breaker as it was happening sooner most times.
I just replaced the breaker and it ran 50 minutes, I left it on while I got ready for an appointment. 20 minutes later I checked it again and it had tripped the brand new breaker. I had cleaned the filters as soon as we brought it home and they still look clean.

Anyone else had, and solved this problem? One other question, this AC is very cold if it stays running for 45 minutes or more before tripping. No mater where I set the temperature I have not heard or felt it cycle off or go to fan only. I can't find any information if that is how it is supposed to work. YouTube is full of videos of Digital thermostat problems and solutions, but nothing about dumb analog knobs.

 

[creativepart]

It could simply be a problem with the 7 year old A/C Unit. Unfortunately, those units are not immune to failures. The first thing folks test is the run and start capacitors. If you're super lucky that's all it is. Otherwise, it can be a compressor going bad and locking up. The refrigerant in A/Cs carries oil to lubricate the compressor. A pinhole leak can reduce the amount of oil present in the refrigerant. And minus enough oil and the compressor will lock up and use too many amps trying to spin. Hence the popped breaker.

If you take it to a shop or have a tech come to you they will check amp draw as a first step and if it's the compressor there's not much you can do short of replacing the unit. Virtually no A/C tech will work on those RV units as they are not considered serviceable.

You do sometimes see someone with a buddy in the A/C business that will modify the unit and make it serviceable, but it's a rare occurrence.

 

[Morich]

I might first start with the simple stuff. One big thing in some areas during the summer is the voltage dropping. Quite simple to check with a meter as well as do some things to check what other points might be going on. Are you running the RV on an extention cord that might be limiting the voltage? In a rural area where equipment is not upgraded as the load grows?
First thought would be to check the voltage from the outlet, especially during hot summer days when local loads may peak. Do give some thought to how the local area works. Are there lots of dairy farms in the area that are prone to hitting the system with lots of loads at one time? It is possible to bring the system down if a lot of milk coolers start near the same time like during the milking periods!
Before I tried to repair my RV, I would first want to verify the system is not the problem!
Where the problem comes in is when the local "good old boy" network is not inclined to force the power providers to spend the money to upgrade to standards as the local load grows over time! Small city systems are more prone to this as the city council tends to not want to spend!
But that is all very much just theory and possibilities until some voltage checks are done!

 

[Waterbug]

Another thought is that something like a water heater set to electric could be switching on., maybe even your AC to DC unit charging the house batteries. EDIT: I would expect a defective AC unit to pop the breaker on start-up. Current draw is much higher then.

 

[B2bear]

It could simply be a problem with the 7 year old A/C Unit. Unfortunately, those units are not immune to failures. The first thing folks test is the run and start capacitors. If you're super lucky that's all it is. Otherwise, it can be a compressor going bad and locking up. The refrigerant in A/Cs carries oil to lubricate the compressor. A pinhole leak can reduce the amount of oil present in the refrigerant. And minus enough oil and the compressor will lock up and use too many amps trying to spin. Hence the popped breaker.

If you take it to a shop or have a tech come to you they will check amp draw as a first step and if it's the compressor there's not much you can do short of replacing the unit. Virtually no A/C tech will work on those RV units as they are not considered serviceable.

You do sometimes see someone with a buddy in the A/C business that will modify the unit and make it serviceable, but it's a rare occurrence.

Thank you. I will put an amp meter on it today and check what the starting draw is. But it always starts and runs never less than 10 minutes so my guess is the start capacitor must be okay. I would like to know what the amp draw is when it trips the circuit but I can't see sitting there for 30 to 50 minutes until it finally happens watching it. Maybe I can find a device that records as well as the voltage somebody recommended watching the voltage. But I have a watchdog unit on the shore power that is supposed to shut off if the voltage gets too low or too high and that is has been yet to happen.

I could see it could be possible to lose some oil and cause the compressor to seize up. But it's unlikely that it would start again these last 30 or 35 times I've had the AC on only to have it trip somewhere between 15 and 50 minutes into being on. My understanding is with a pinhole leak it would lose enough freon as well as oil to cause a low pressure switch to kick in and prevent the AC from ever starting. I've had that problem on my truck.
Thank you for your input.

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[creativepart]

My understanding is with a pinhole leak it would lose enough freon as well as oil to cause a low pressure switch to kick in and prevent the AC from ever starting. I've had that problem on my truck.
Thank you for your input.

I don't think that applies to RV A/C units. The two A/Cs I had failures with simply lost refrigerant and the compressor seized. The only way to know this had happened was when the A/C started blowing circuit breakers... and hot air.

 

[RayIN]

Capacitors do weaken with age. Since they are not expensive, I'd go ahead and replace both start and run caps just to eliminate that as a cause.
Any refrigerant oil leak will leave a stain and/or wet spot, which is quite obvious to most people; it does not evaporate into the air.
I suspect a weakened compressor motor from having been operated on low-voltage several times. Low voltage is not an immediate failure, it "bruse's" the motor with each occurrence, this brusing is permanent and cumulative. Low voltage is: nameplate voltage minus more than 10%.
Measuring running amp-draw is key to determining motor health.

 

[DCSCO]

Congrats on your 170S, my wife and I have a 2018. The previous owner replaced our ac just before we purchased it 2025.

I do have a background in HVAC, so here goes. The trip curve for a typical 20amp circuit breaker would be 210 minutes on a 21 amp load with trip time dropping to instantaneous on a direct short. If you can measure amps at the circuit breaker you will get the first clue. The unit may be running a little over rated amps or something in the unit could cause a short to ground during some point during operation.

See attached

 

[That camper guy]

I just bought a 2019 MD170S that has not been used for the last 4 years. We tested the AC while inspecting prior to purchasing. It was on around 40 minutes. When we got it home we put it on Shore power. The AC would run only 30 to 60 minutes and then pop the breaker. At first I thought it was due to running it on low and could be freezing up since it was nice and Cold. So I tried it on High but lower on temp (it doesn't have a real thermostat to set temp). Still would only run 30 to 40 minutes, sometimes as short at 10 minutes before tripping the trailer breaker.
I came to believe that it was a weak breaker as it was happening sooner most times.
I just replaced the breaker and it ran 50 minutes, I left it on while I got ready for an appointment. 20 minutes later I checked it again and it had tripped the brand new breaker. I had cleaned the filters as soon as we brought it home and they still look clean.

Anyone else had, and solved this problem? One other question, this AC is very cold if it stays running for 45 minutes or more before tripping. No mater where I set the temperature I have not heard or felt it cycle off or go to fan only. I can't find any information if that is how it is supposed to work. YouTube is full of videos of Digital thermostat problems and solutions, but nothing about dumb analog knobs.

As a retired HVAC and commercial refrigeration guy I can tell you that compressors can sometimes get "stuck" after sitting. Residential fridges are famous for that. But all is not lost. If you can find a real refrigeration mechanic who knows his stuff he can: A. Tell you why it's drawing high Amperage and 2. If it's stuck from sitting he can give it a jolt out of phase which can usually break the stuck mode. Sometimes just a hard start kit will do it. Good Luck.

 

[DCSCO]

The wiring diagram shows two loads, the compressor and the fan motor. The fan motor must be dual shaft to run the indoor evaporator fan and the exterior condenser fan on the same motor. I would inspect electrical connections. A FOP, fall of potential test, with good meter set to AC volts that can read milliamps, place one lead on the circuit breaker output and the other on the fired wiring connection.

Over 75 MA would indicate a poor connection