Heat Pump moisture

At today’s inspection I observed dripping water coming out of the exterior pad mounted unit heat pump.It is suspended up on about 6" legs sitting on the pad.
Is it normal to have water dripping from it.
It seems to me that of water drips from it during the winter, it would build up into a big block of ice & be a problem with heaving of the unit etc.
The outdoor temp was about 40F.
Does the water dripping cease after it gets cold or is this a problem that needs to be fixed?

Roy Drangstveit

Its normal it just went through a defrost cycle and that is why its elevated to allow for ice build up

I will also make a strange noise when going in defrost and steam up.

On a timer, for the heat pump to perform well, the heating element will generate heat that will melt iced water on coil in cold weather. When this happens the Heat pump is technically on an air conditionning cycle. When the coil has melted the ice, the reversing valve switches back from the air conditionning phase to the heating phase.

You got part of it right…:wink:

Yup, partly…

The Heat Pump Defrost cycle is probably the most complex operation in the heat pump, so we won’t get into it here.

There are several defrost systems: Time -Temperature; Time- Refer Pressure; Time - Air Pressure - Temperature; Time -Air Pressure - Reefer Pressure…

Something starts the cycle and something else stops the process.

Electric heat does not melt the ice. Heaters are downstream to the evap coil.
Heaters prevent a cold blast of air when in defrost. The heat to melt outdoor ice comes from the heat pump’s previous cycle.

There is less water, because there is less water vapor in cold air than when it is 40F outside. But it will always drip. As for ice build-up, if ice makes it up to the bottom coil, the unit will stay in defrost longer and melt this ice. It is more of an energy loss problem (not to raise the unit above the ice) than the ice on the coil. Contact with the hot outdoor coil and hot water running off the coil will melt more than it will freeze (unless the defrost cycle is not correct).

So if you see ice build-up into the OD Coil, there is a defrost problem.

If you have a low refrigerant charge, sensor out of calibration etc. this type of thing will result.

If you see stripes of ice on the OD Coil and they do not go away after a defrost, you have a low refrigerant charge (Very Low).

Just reading this post and I had a very similar situation the other day. The heat pump is dripping water all the time and the ground around the heat pump is soaked almost a mud hole. Is this much moisture from the unit normal as well. I’ve just never seen it this bad.

Brian Cummings 021.jpg

Also the temp around here has been in the 50s to 60s around the time of this inspection

That appears a little much I am thinking of one situation where it could cause that much water on the ground and it being if the unit was low on Freon and was icing premature on the exterior condenser/evaporator thus creating a premature defrost cycle could be a possibility thus the extra water. Me thinks it should be checked by a HVAC tech

I had to turn my heat pump off and use the EM Heat setting because of outdoor air conditions last week.

Fog conditions at near freezing temps froze the OD Coil in minutes and blew cold air till the defrost cycle came around…

Alabama, gulf moisture and heat operation = lots of water.
If you have a lot of water on the ground, there is a lot of water vapor in the air.

A Heat Pump can’t “make” water from nothing.

It makes the most water when it is operating correctly.

So, if it is making lots of water, it’s working right.

Gulf coast or not I’m still skeptical that is a lot of water:shock:

where else would it come from ?

When it’s 50° and 95% humidity and it touches 40° suction line/compressor we make water. Only other option I can think of. Unless it’s not associated with the HVAC.

I think it’s just acting like a big outdoor dehumidifier.

Does not matter that its 50 outside if its low on freon the exterior evap is going to freeze in the heat mode then its gona defrost starts short cycling creating more ice and water

How does a A/C unit form ice in 100 degree temp in the summer time;-)

Not really.

An under charged HP will not sub-cool the entire surface of the OD Coil and will not produce the same quantity of frost as if it were fully charged. It happens faster, but not as much.

As for the 50F temp, that air has the capacity to hold more grains of moisture per pound of air than colder OA. When it gets into late winter and the OD Temps go down and stay down, this moisture is squashed out of the air. At 17F the unit may never go into a defrost cycle…

Just as in the 1st Law of Thermodynamics, energy can not be created or destroyed (except nuclear). Condensate is about heat energy (about 970 btu/lb water).

No a low charge will not frost the complete coil but it does frost and depending on The MFG how they iniatate a defrost will and does create short cycle of the reversing valve.

Notice my first statement was a possible cause its hard to trouble shoot from afar;-)

That’s for sure!

Especially when the OP doesn’t know what they’re looking at.

yes sir, you are correct. If the defrost system is initiated by pressure it will cycle rapidly. But I would venture a guess that in this particular case the unit is fine and just doing what it does.

Under our current weather conditions here and down in Alabama, a low charge would look like a zebra in pretty short order… The humidity has been so high, I have had to put several thermal roof inspections on hold.


No temp drop after sundown (arrow).

Fog event (circle).

If you guys do a roof scan and don’t find anything and see a weather graph like this, you better go back! :wink:


This is what you want to see (if you were wondering)…

Thanks for the replies. I did recommend further evaluation by a HVAC guy and he did find the freon a little low. There may not be a problem but I did not know so I recommend.

Just for your information, there is no such thing as “a little low” with a heat pump operating in the heating mode.

You only utilize a small percentage of the refrigerant to produce heat in the winter in comparison to removing heat in the summer.

If the refrigerant level was low enough to affect its operation in the heating mode, it requires a lot more than “a little” to bring it back up to a full charge.

I think ya did the right thing David has been getting up on the wrong side of the bed lately:D:p