Dehumidifier failure mode?

[CvW]

Hi all,

 

I have a question regarding a couple of dehumidifiers that I installed in my in-laws basement, circa 8/2011. They are fad704dud frigidaire 70 pint/day units hooked up to drains so no bucket emptying is usually needed. All three were running for a long time on initial hookup to dry out the basement, controlled it.

 

This year one unit kept running but produced no condensate, I diagnosed it as sealed system failure and the company was nice enough to offer a refund on the purchase price. 

 

The two remaining units are producing condensate but also ice up almost immediately on startup. I am scratching my head re: this behavior given that it's about 65-70*F in the basement and the humidity is only 65-70%. In other words, these units shouldn't be featuring a evaporator HX that is half clogged (growing from the bottom to halfway vertical on HX) with condensate after just 1/2 hour runtime. 

 

The replacement unit I bought (FAD704DWD) has a noticeably higher discharge temperature and almost no condensate frosting, even after a full day of non-stop running under similar conditions. The two older units ice up so badly that the condensate buckets fill over time from ice forming on the bottom of the drain pan (above the bucket) and dripping down. 

 

So here is my question: Do you think that the remaining two units may be on the verge of suffering from a sealed system failure also? That is, is the system so starved for refrigerant that the evaporator is cooling too effectively, leading to instant ice formation? 

 

I have put the two remaining units on interval timers to limit ice growth but am thinking that may not be sufficient a band-aid. If 1/2 of the HX turns into a ice block within 1/2 hr of operation while in a warm basement with relatively benign humidity levels, something is off... Any insights are appreciated. Thanks! 

[RegUS_PatOff]

... The two remaining units are producing condensate but also ice up almost immediately on startup.

pictures ?

is the Fan running OK ?

[CvW]

Hi, the fan is running, though the outputs do not seem quite as high as on the -DWD unit. Could be the icing. As far as a picture goes, here is a frontal shot with the water bucket and air filter removed. 

. The evap is about 75% covered in this picture, about 3/4 of an hour after startup.

[CvW]

FWIW, the speed of icing seems to be correlated to the ambient humidity. When the humidity is around 60-65%, one of the two -DUDs is not icing at all, the other is still icing quickly. Icing was almost immediate in 80% conditions. The DWD has yet to show any icing despite similar conditions.

 

In the meantime, I have taken a look around the web. It appears that if all other variables can be eliminated (i.e. dirty filter, low fan speed, dirty HX, etc.) that low refrigerant charge can be a fairly cause of evaporator HX icing, especially when it is humid and cool at the same time. 

 

Methinks that the remaining DUDs are probably low on charge (one more than the other) and hence on their last legs. Correct me if I'm wrong, but given that these units do not feature schrader valves, it's likely uneconomical to have them recharged?

[RegUS_PatOff]

I'm not a sealed system master, but, yes, looks like a low charge from a leak.

Schroeder valves can be installed, charged, then sometimes they actually remove the Schroeder valve and crimp & solder.

But may depend on where the leak is ... (to be repaired)

but may or may not be worth it on a Dehumidifier