Dehumidifier challenge

I am stumped by the behavior of my Whirlpool AD50USR dehumidifier.
I have the dehumidifier mounted on a shelf in my basement with the drain flowing into the washing machine drain pipe.
Everything worked fine until I took it down for a day to use in another room.
When I put it back up, it still did all the usual fan blowing and cycling of the compressor, but the volume of water dripping into the container slowed by 90% or more.
Interestingly, when I put it back down on the floor in the same basement room, it started working perfectly again.
When I took another identical unit and put it on the shelf, it too slowed down markedly but worked perfectly again back on the floor.
Note: 1. The shelf is perfectly level 2. There is reasonable ventillation on all sides (plus it did work before; also it works on the floor even when the ventillation there is artificially constricted even more than when on the shelf) 3. There is plenty of humidity in the room at all heights (plus if the humidity were too low at the higher height, the unit would have shut off) 4. The temperature of the exhaust air is about the same whether on the shelf or the ground, suggesting that the refrigerant is being compressed the same. When I removed the cover, the front coil felt cold though I did not compare the cold temperature in both cases. 5. The cycle time, the fan noise, the compressor noise, etc appear the same in both situations.
About the only difference between the two setups is the height and the fact that when mounted on the shelf, the shelf slides under the unit between the wheels vs. the floor situation where it rides on the wheels directly (however, as stated before the unit is level in both situations).
I am stumped, particularly, since it worked before but now neither unit works on the shelf and I can't think of anything that has changed?
Is there anything subtle I could be missing or is my house just haunted :)?
Thanks
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The air is more humid when close to the floor and drier higher up. Feel your floor I bet it feels a lot cooler than an object that is above the floor. Damp air is always cooler lower and that is what kicks the dehumidifier on.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I don't think this explains it for several reasons: 1. If the humidity were really so low that little or no water can be extracted, then the humidistat (which is set at a 'middle' setting) should shut off at least occassionally; however, my problem is that the humidifier runs non-stop yet doesn't generate much water.
2. The humidity at the shelf level when measured is not that different from floor level
3. The humidifier had worked well there in the past with similar ambient humidities
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Get a hygrometer and measure the humidity at floor level and on the shelf. Quit guessing.
Stretch
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No guessing. Have 2 hygrometers and checked them both. Difference of at most 5% between floor and shelf. Both readings above 60% and above shutoff point for hydrostat. From experience, I know that the 5% difference is not the reason for the drastic difference in output.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Something with the hose?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Problem occurs with or without hose attached (Note dehumidifier first drips into a bucket and host only takes away the overflow).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Call the Ghost Busters.
You may have the discharge air from the dehumidifier recirculating when the unit is on the shelf. This would cycle the unit off more and/or reduce the amount of humidity entering the dehumidifier inlet. I have used and sold these units without any problems.
Good luck.
Stretch
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.