Heat Pump blowing moist air

[stevejones]

Hello,

We're in a 2019 Globetrotter 27 FBQ with two AC units. We are currently in Melbourne Florida. Yesterday we had rain most of the day.

This morning got up and since there was a bit of a chill turned on the heat pump. When it came on, the air coming out of the vents was so moist it increased the humidity inside our trailer from about 60% to over 90% in about 10 minutes as shown on our hygrometer. This of course caused a serious condensation problem since the inside of the trailer was cold. We turned the HVAC system off.

Later in the day I again tried turning the heat pump on, and again it was blowing out moist air.

Anyone have any ideas why this is happening?

Thanks,

Steve

[glcmranger]

Try using your furnace!!

[Al and Missy]

It sounds like there is a leak allowing water to pool in the housing which is then blown out when the unit turns on, or an air leak allowing outside air to get to the inside of the unit.

The unit should still be under warranty. There is a large RV dealer (Giant Recreation World 321 242-6261) right at the Palm Bay Road exit on I-95. Exit west and turn south (left) at the light at the first entrance to the mall. You can see the dealership from I-95, but maybe not from the north.

Al

[Caffeinated]

The same thing happened to us on a cold wet day here in the PNW. I was concerned, but as it was cold, we left the heat pump run. Within about an hour the heat warmed up the trailer and the condensation evaporated. So, no harm, no foul. If it's really wet and cold out it might be better to run the heater.

Mike

[J. Morgan]

After spending all night in the trailer the moisture you exhaled all night was present, it just wasn’t in the air. It was on surfaces, in blankets etc.

When you turned the heat pump on, the warmed air was suddenly able to hold moisture and the relative humidity went up quickly in the confined space.

At this point of course the walls were cooler than the circulating air so condensation formed quickly.

A) A heat pump is incapable of adding moisture to the air, and

B) the moisture contained in your 98 degree breath HAD to go somewhere even as the cool air was incapable of holding it for very long.

The heat pump SEEMED to cause the total moisture level inside the trailer to rise but almost certainly that isn’t the case, it just moved it into the air from surfaces, textiles, etc.

IMHO a furnace would have done the same thing but not as quickly because the two heat pump units move A LOT of air as compared to your single furnace, so the two heat pump “dried” your trailer very quickly moving settled moisture into the air very efficiently.

Also consider that the humid air that had come into the trailer before the night chill had moisture in it. This moisture settled out as it cooled and added to your exhaled moisture that I mentioned above.

(We Americans aren’t really used to the pitfalls close space living..... )

[stevejones]

So yesterday afternoon we opened most of our windows and just ran the heat pump for a while. Moist air initially but then dried out. Ran the heat pump all night and all was well.

However this morning noticed a drip down the side of the trailer so I think the AC drain might be clogged. If the pans beneath the units held a puddle of water from all the rain we got, could that result in the unit picking up moisture from an air intake?

Thanks,

Steve

[Belegedhel]

The explanation provided by J. Morgan above is very plausible--imagine driving down the road in your car in the winter with the heater running. If you switch the airflow controls to "recirculate," you are closing off fresh air from outside the vehicle and recirculating the interior air, which becomes increasingly humid as the passengers breathe. Eventually, the windows start to fog. This is essentially what is happening in your trailer, but there may be something else wrong with your heat pump as well.

Your heat pump should be built so that it sucks in air from the interior of the trailer, runs it through a heat exchanger, and then spits it back into the interior. The inside of the unit (where your cabin air is circulating) should be completely sealed from the exterior of the unit. You will have "penetrations" of the housing of the unit, where coolant lines and electrical wires go from the outside to the inside. I found on my AC unit, that these penetrations were sealed with some kind of mobile butyl goop, and the goop had sagged, allowing the unit to suck in humid air from outside the unit.

There should be a mechanism for catching condensate that drips off the interior heat exchanger coil and funnels it down to the ground. If this drain gets plugged, you could have a puddle of water sitting underneath your heat exchanger coil, and as air passses over the puddle, it could be picking up additional moisture. This could explain why you are seeing water drilling down the outside of the trailer. On the other hand, if you are in heating mode with your heat pump, this would suggest you are moving energy from the outside of the trailer to the inside via the external and internal heat exchanger coils. If your exterior heat exchanger is below the dew point, you are going to get condensation on the external heat exchanger. If this fluid is just treated like rain water, then it is going to drip down the outside of the trailer.

Good luck!

[stevejones]

Thanks all for the helpful info. I'm going to try to clear the AC drain but also be mindful of outdoor and indoor conditions when I run the HP.

Thanks,

Steve

[Wazbro]

Originally Posted by stevejones

So yesterday afternoon we opened most of our windows and just ran the heat pump for a while. Moist air initially but then dried out. Ran the heat pump all night and all was well.

However this morning noticed a drip down the side of the trailer so I think the AC drain might be clogged. If the pans beneath the units held a puddle of water from all the rain we got, could that result in the unit picking up moisture from an air intake?

Thanks,

Steve

Drip down outside trailer is normal, as designed. The outside condenser is designed to just drip on roof while used for heat.

Most of the time the humidity is low when you need heat so the engineers believe there isn't enough water to worry about.

[HHPJ]

Originally Posted by Wazbro

Drip down outside trailer is normal, as designed. The outside condenser is designed to just drip on roof while used for heat.

Most of the time the humidity is low when you need heat so the engineers believe there isn't enough water to worry about.

I agree, heat pump condensation runs down the side, AC through the wheel well....

[Life is a Highway]

Could be a warranty issue as our new trailer did the exact same. Trailer has to be level before condemning it .

Ours was a up top kinked AC drain hose from the factory in combination with the drain hose in the interior wall being partially restricted.

Dealer had to install an elbow then blow air down the tube to clear it out and
“ stretch the hose “ I can’t verify that repair if it worked? As our new Airstream trailer was side swiped in the service department and it never came home. We refused to take it back. New one is ordered.

Originally Posted by stevejones

So yesterday afternoon we opened most of our windows and just ran the heat pump for a while. Moist air initially but then dried out. Ran the heat pump all night and all was well.

However this morning noticed a drip down the side of the trailer so I think the AC drain might be clogged. If the pans beneath the units held a puddle of water from all the rain we got, could that result in the unit picking up moisture from an air intake?

Thanks,

Steve

[stevejones]

Originally Posted by HHPJ

I agree, heat pump condensation runs down the side, AC through the wheel well....

Thanks. Looks like the AC is draining out the wheel well, and the HP is down the side of the trailer. So I don't think I have a plugged drain after all. After reading all the posts on this thread and doing research I think everything was working as it normally works and I just need to be mindful of outdoor conditions before using the HP.

Thanks for all help

Steve

[GandW]

After full timing for 2 years, I found that when the humidity in the trailer is high and you use the heat pump the relative humidity will go up. The heat pump does not produce condensate. The same amount of water is in the air, but the "relative" humidity goes up. While it sounds counter productive, plug in a small space heater on low to warm the trailer and then turn on the cool on the AC. Leave the space heater running. The AC will remove the moisture and drop the humidity in minutes and dry everything out. We do it all of the time when its been raining for long periods of time and the humidity goes above 60%. You can't put the heater on high as you will trip the breaker.
This is standard practice in grocery stores because of all of the coolers putting moisture into the air.

[Baby Zeppelin]

We camped in Florida last week and had the same situation the OP noted - heat pump ran early in the morning and condensation formed on the walls and fogged the bathroom mirrors.

I initially thought there was a problem until realizing that my wife had turned on the coffee percolator when she got up at the same time I turned the heat up.

The real culprit was the steam from the coffee maker. I could see that the area of the ceiling around the warm heat pump vents was drying off, as it was battling the humidity, not creating it. Once we finished our morning coffee all was well. In the future we'll have to remember to turn on the stove vent fan to suck the steam outside.

[OCRV]

2023 Flying Cloud and we experienced the same problem. AC works great, heat pump causes condensation. Furnace does not cause condensation. We’ll have the dealer check out drains, drain lines etc but reading all of the posts it sounds like this is not unusual. Given that an Airstream is a very small space it does take much to cause the condensation. BTW, the outside humidity was over 70%. We had only run the heat pump once before and no condensation. Did not check humidity as there was no reason to do so.

[TNOutback]

Resurrecting this topic. 2023 Flying Cloud 25RB with two rooftop a/c units. While camping this weekend, we ran the front unit a/c for a while during the heat of the day. Unit appeared to be draining properly into the wheel well. Turned the unit off late afternoon and opened the windows. Later that night, we closed up and turned on the front unit on heat pump mode to warm the camper. The unit started putting out warm really moist air, so much so that all surfaces in the camper were quickly covered in water, dripping down walls, cabinets, etc. Our temp/humidity monitor went from around 60% to 95% in just a matter of minutes. Turned the unit off and used a bath towel to wipe down walls and ceilings.

I then turned on the rear unit in heat pump mode and it worked as expected. It did NOT dump out a lot of moisture. Two separate units, two very different experiences. What is going on with the front unit?

[dznf0g]

Originally Posted by TNOutback

Resurrecting this topic. 2023 Flying Cloud 25RB with two rooftop a/c units. While camping this weekend, we ran the front unit a/c for a while during the heat of the day. Unit appeared to be draining properly into the wheel well. Turned the unit off late afternoon and opened the windows. Later that night, we closed up and turned on the front unit on heat pump mode to warm the camper. The unit started putting out warm really moist air, so much so that all surfaces in the camper were quickly covered in water, dripping down walls, cabinets, etc. Our temp/humidity monitor went from around 60% to 95% in just a matter of minutes. Turned the unit off and used a bath towel to wipe down walls and ceilings.

I then turned on the rear unit in heat pump mode and it worked as expected. It did NOT dump out a lot of moisture. Two separate units, two very different experiences. What is going on with the front unit?

When you ran the front unit on a/c, the evaporator and internal drip pan remained wet (normal). When you switched over to heat pump, you evaporator now becomes the condenser and gets hot. That would rapidly evaporate the water on the fins and would more quickly evaporate any water in the drip pan.

Your rear unit was unused on a/c and was dry, so there was no humidity generated by that unit.