Hello, Dave,
Hope your Labor Day permitted some relaxation for you. Mine became a little stressed when my 30-amp motorhome and a surge protector suffered a two-second brownout while connected to a campsite pedestal. My Dometic rooftop air conditioner was running during this time. It never really shut down, but when power was fully restored, the smell of burning plastic was present inside the motorhome.
The unit performs flawlessly, cycles normally blowing cold air as it should, and the odor dissipates. Should I be concerned and, if so, what should I look for? Thanks for the assist. —Karl, 2019 Gulfstream BT Cruiser 5230B
Hi, Karl,
I would definitely say my Labor Day weekend was much less stressful than yours, mostly picking between white or red!
As I have stated many times, I am not an electrical expert. So I consulted my good friend Steve, who is an RVIA Master Certified Technician with more than 35 years of experience in the RV industry. He was Winnebago’s Appliance Repair Manager as well as the Manager for Wire Prep for 30 years.
Causes of brownouts
Steve indicated that an electrical brownout is a drop in voltage that could be unintentional or intentional. An unintentional brownout situation at a campground would be caused by a sudden excessively high electrical demand such as several air conditioners starting a cycle at the same time. This would explain the 2-second time frame you experienced. An intentional brownout is when the power company initiates a load reduction during high demand situations, which I doubt was the issue in your case as these are much longer.
Steve did have a few questions.
“During the brownout, did you see the voltage at the surge protector. If so, what was it?”
Unless you have a surge protector that has Bluetooth capability to your phone, I doubt you were able to actually see the voltage, but rather experienced a lower motor speed of the roof air conditioner and maybe dimming lights.
Did you notice if it happened when the air conditioner started the initial start or cycle or the compressor was running?
You stated that the roof air conditioner was running but did not indicate if it was just the fan running or the compressor, and if it was during the initial startup of the compressor. If you have the thermostat set to the A/C operation and the fan on position, the fan will run continuously to circulate air. If it is set to Auto, the fan will only come on when the compressor comes on.
It is a little deceiving as it seems the air conditioner is running; however, if it is only the fan it draws very little amps.
Initial air conditioner startup
During initial startup, the typical roof A/C pulls almost 45 amps for about 2 seconds and then drops down to 14 amps or less. This could be higher with a dirty filter or restricted airflow in the evaporator coil.
If you can identify whether the brownout occurs during the initial startup or when the compressor is actually running, it could be a high amp draw from the capacitor of the roof air conditioner and not the power supply.
If the filter is clean and there is sufficient airflow during startup, then you will need to have the amp draw verified, IF this is happening during startup. This would be a good time to look at a SoftStartRV™ product.
Remove the roof A/C cover to inspect
This would also be the time to remove the cover of the roof air conditioner and inspect all wiring and connections to verify there is no corrosion, melting, or burned components. This could be the source of your burning plastic smell.
Should you be concerned about the burning plastic smell?
Yes, this smell indicates there was a high amp draw, loose connection, or possibly a low gauge wire. Start with the roof air conditioner, as stated earlier. Remove the plastic cover as well as the evaporator metal shield and look at all the wires and connections at the capacitors, compressor and motor.
Next, remove the cover to the distribution center and look at all the connections to the circuit breakers and 12-volt fuses. I would suggest getting this checked by a certified electrical technician.
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Dear Dave,
I have two questions: What soft start device would you recommend for this camper? How can we make the A/C unit quieter? Thank you. —Ray, 2019 Wolf Pup 16FQ
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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Why do they always say check “check the air filter”? The 1/4 inch thick filter they use isn’t worth the powder to blow it to hell. Rubber, washable junk. The only thing they keep out is (are) insects. A dirty air filter reduces airflow that could cause evaporator icing but you would notice reduced airflow.
I would also check the wiring in the Automatic Transfer Switch – if equipped with a genset. With or without a genset, the 120 side may have taken a hit too.
(I had an ATS burn the wires off – it was a unit used before the genset dominant model I have now).
Thank you, Dave! 🙂 Sounds like a good Labor Day was had by you. 🙂 I find it interesting that the air conditioning unit seems to be functioning perfectly despite the burning plastic smell that occurred. Were I in that position, then I’d call an electrician. Alternately, DW would have me get the extension ladder from a storage bay, extend it, and hold it as she climbs to the roof to investigate things closely. I don’t much mind, I’ll hold the ladder for the electrician or her, makes no particular difference to me. 😉 Thanks again, have a great week, safe travels, and safe stays! 🙂