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Old 11-01-2017, 09:15 AM   #1
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2017 Heat Pump Condensation Roof Runoff

Greetings Streamers:

I have read some interesting posts from a few years ago on Heat Pump Condensation runoff onto the roof and down the side as normal. The AC runs into a drain by the wheel well.

On the 2017 and newer AC redesign, is this still the norm for Heat Pump Roof runoff?
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Old 11-01-2017, 10:36 AM   #2
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Originally Posted by HHPJ View Post
Greetings Streamers:

I have read some interesting posts from a few years ago on Heat Pump Condensation runoff onto the roof and down the side as normal. The AC runs into a drain by the wheel well.

On the 2017 and newer AC redesign, is this still the norm for Heat Pump Roof runoff?
Perhaps the condensation is from the air inside being warm and the outside air cold. It's not from the AC as much as from the cold air. I noticed it also on the back of the fridge outside.
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Old 11-01-2017, 10:44 AM   #3
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HVAC Drain

Mine drains by the wheel well. 2017 30 FC Bunk
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Old 11-01-2017, 10:45 AM   #4
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Normal
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Old 11-01-2017, 02:32 PM   #5
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Our 15k Dometic on our 27fb drains some condensation onto the coach roof when in heat pump mode as well. Seems to depend on outside temp and humidity conditions. Must be condensation from components that don’t drain to cups that connect to wheel well hose for A/C mode condensation.

Hope this helps.
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Old 11-02-2017, 11:58 AM   #6
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an aside question re: heat pump. Why use it at all? Seems to make alot more noise and the furnace seems to do alot better job.
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Old 11-02-2017, 01:49 PM   #7
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2017 Heat Pump Condensation Roof Runoff

With hookups, unless you’re paying separately for utilities, the electricity is “free.”
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Old 11-03-2017, 01:03 PM   #8
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My 15k Dometic discharges a lot of condescension on the roof while in heat pump mode while in AC mode the condensation drains between the tires. My limited understanding is that this is normal due to the HP running in reverse of AC. My understanding is that while running in reverse different components condensate than when in AC mode.
The HP is good at removing moisture from the interior vs the propane heater.
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Old 11-03-2017, 02:17 PM   #9
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2017 Heat Pump Condensation Roof Runoff

Yep the outside coils that you see turn cold in heat pump mode. In damp weather the coils may ice. The defrost cycle will melt that ice in most cases, but not always. One rainy cool fall in Branson we truly iced up and the defrost cycle did not clear the ice. The ice got so bad that the unit was only blowing luke warm air.
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Old 11-03-2017, 03:38 PM   #10
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It is normal

The condensate, that forms when the heat pump is running in heat mode, is from moisture that collects on the outside coils, the part of the air conditioner exposed on the roof. The more humid the exterior atmosphere the more condensate forms on the exterior. This is just the opposite of what happens during cooling mode, when the condensate forms on the interior coils.

In heat mode:
If the conditions are right (low humidity and/or warm temperature), the condensate can evaporate as fast as it forms. No condensate will drain.

If it is humid enough and the just right temperature, the condensate can form as liquid. If it forms and drains fast enough one can see it dripping.

If it is humid enough and cold enough, the condensate can form as frost on those outside coils. If the outside temperature is warm enough to melt it at the end of each heating cycle it will melt and drain.

If it cold enough for the condensate to freeze continuously and build up a layer between cycles, the heat pump will go into a defrost mode. The compressor runs, the refrigerant directional valve changes (similar to cooling mode) to create heat in the exterior coils, but the fan does not run. This cycle will last only long enough to melt the frozen condensate that has collected on the outside coils. Melted condensate can run/drip during the defrost cycle or will be blown away from the exterior coil when the fan comes on. I've seen this look like a burst of snow, on my heat pump at home.
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Old 11-03-2017, 06:16 PM   #11
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We had the same question some time ago. Our dealer said it's perfectly normal to have water running off the roof while running your heat pump in "heat" mode.
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Old 06-28-2021, 08:47 AM   #12
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A/C roof condensation

I know this is an old thread but I’m posting the same question here about roof condensation but with the unit in straight AC mode. We are camped in Fla and it’s hot and very humid. AC is running nonstop. The wheel well drain is dumping like an open faucet. So that much I know is working. From what I can see from my not talking enough stepladder. It appears that there is condensation all over the roof but especially around the AC unit itself. Which of course is dripping down the sides of the trailer. Is this normal? Again it’s very humid. High 80’s but feels like high 90’s.
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Old 06-28-2021, 09:17 AM   #13
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Correction:
‘Not tall enough stepladder’

These smart phones can be real stupid sometimes
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Old 06-28-2021, 05:01 PM   #14
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<<snip>> It appears that there is condensation all over the roof but especially around the AC unit itself. Which of course is dripping down the sides of the trailer. Is this normal? Again it’s very humid. High 80’s but feels like high 90’s.
IMO, Condensation forming all over the roof and around the AC is probably caused by the thin insulation between the interior AC duct and roof exterior. The condensation is there because the temperature of the roof metal is below the dewpoint of the outside air.
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Old 06-28-2021, 05:43 PM   #15
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My last experience with condensate freezing was when my trailer was fairly new. Unless things have changed, Air conditioners with Heat Pump capabilities went into defrost mode after running for a continuous amount of time in Heat Pump mode. My dealer never had told me that and the first time that happened I thought the fan had broken. At the time it occurred the unit shut down and a few minutes afterwards you heard the compressor start up but with with no fan running. The unit ran in that mode for a fixed amount of time, shut down and started up again, this time with the fan running and heat being produced. There didn't seem to be any intelligence that the unit could detect ice on the coils. It seemed to truly be a timed event.

What proved that was one cold fall day in Branson, Mo where it was on and off rain and temps were in the low 40's. We had left the trailer for the day and when we got back a few hours later, we found that the heat pump was running but it was in the 50's inside. The air coming out the air conditioner was very tepid. I went back outside and looked at the outside coils and found them encased in a block of ice. I've attached a picture to show you what it looked like. This is from Oct 14th, 2004.

After talking to the dealer he noted that the defrost cycle was timed event on my unit and with almost 100% humidity and the rapid calls for heat, the ice on the coils had not completely melted. To make matters worse that lessened the discharge air temperature inside and as the calls for heat occurred more frequently, ice was building up on those outside coils. As the build up of ice continued on the outside coils, the ability of the coils to pull heat from the outside air decreased. That continued to reduce the discharge temperatures of the air blowing out inside the trailer. Even with the run times getting longer and defrosting occurring more often, the ice was building up faster than the timed defrost cycle could melt the ice on the coils.

So the lesson I learned was once temperatures outside dropped below 45 and it was very humid outside I never left the trailer unattended with the heat pump on and instead set the thermostat to the furnace setting rather than heat pump. Never have had a freezing event since.

I'd be curious if the technology has changed over the years and whether the current heat pumps have some sensor that can detect air flow loss caused by the outside condenser icing up which in turn would cause the defrost cycle to fire up, rather than depend on a timed run routine. Or maybe the defrost cycle logic has changed to provide more run time.

Jack
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