MrCool 12k 1st day. Cools well; but strange problem?

[Will S.]

I finished the MrC yesterday afternoon, did a leak check using the Blue bubble leak check, and ready to go. Installed in an above-garage bonus room, about 570 sf, 2 windows, glass entry door & a SGD to a deck. Insulated R19/R30, and rocked, but with lots of southern exposure and over a hot garage, it is always in the mid-90's up there.

Yesterday was no different. Outside temp upper 80's; bonus room 93. Powered up the unit around 3pm. Set it to COOL, and temp to 80, just for starters. I have a remote thermometer which agrees with the temp display on Mr C. When checked at 9pm, it was showing 79/80. I went upstairs to raise the set temp to 82 (I don't need it any lower for the moment). I also set the MODE to DRY, as humidity has been in the 80's-90 lately.

This morning the temp was 73! What's going on? Set temp still showed 82, MODE DRY. I changed mode to COOL, left temp setting alone, and the temp has gone back to 80 as of 11:15AM. Why would DRY mode keep lowering the temp? Is that normal?

 

[sleek98]

It will run the AC to pull out the humidity.

 

[PoorOwner]

Dry mode doesn’t have a set temperature. Just use the AC mode

 

[Will S.]

Thanks for the replies. The manual is what confused me. In the Remote Manual, under dry mode, it states: "Press the Mode button to select DRY mode. Press the UP/Down button to select the desired temperature. The temperature can be set within a range of 62*F - 86*F in 1*F increments."

So I didn't know that it would keep dropping the temp below the set point; a detail they left out. Good to know it's working correctly.

 

[PoorOwner]

I don't know.. it may take it as a suggestion but not keeping promises, it runs the compressor fairly hard and then stops for a while, and repeat. I recommend not use it, if you have as much heat up there as you say, and your 12K is not oversized for the room, it should continue to pull condensate just about all day long in regular AC mode.

 

[Richard Cranium]

It will pull condensation every time the compressor runs.

 

[Will S.]

Yes, I agree. The only reason I thought of putting it in the "Dry" mode was that I thought it would run at fewer BTU's, but continuosly; like having an undersized AC that just runs, pulling humidity out and never reaching a set point. I don't plan to use that mode again. It will work just find, on Cool mode, either automatic, or just ON. Not sure about that yet, but I'll experiment.

Thanks again.

 

[sgiss]

It took me quite awhile to figure out the Mr Cool manuals - and I had to read manuals from other brands to understand DRY MODE. What is does is run the fan at the lowest speed possible to maximize dehumidifying. It will also cool in that mode, but priority is dehumidifying. P.S. You have a refrigerant leak, like I did, you will likely find it in DRY mode first!

 

[Will S.]

It took me quite awhile to figure out the Mr Cool manuals - and I had to read manuals from other brands to understand DRY MODE. What is does is run the fan at the lowest speed possible to maximize dehumidifying. It will also cool in that mode, but priority is dehumidifying. P.S. You have a refrigerant leak, like I did, you will likely find it in DRY mode first!

Please explain a little more about why and how you found a leak?

 

[Bills Tools]

Dry mode will overcool to dehumidify. It’s looking for rh not temps

 

[Dagny]

In dry mode both high and low side pressures will be lower.

 

[yeldogt]

Some systems have a humidity setting that will allow the unit to "overcool" a set number of degrees. You can set the desired humidity and the amount of overcooling you want. On cooler humid days it's important to continue to remove the humidity as this will effect comfort. Many of the base mini split systems just have the "dry" setting that sets the unit in a static position to minimize the cooling and max the humidity control .. it's manual and needs input from the owner.

In a hot dry climate -- it's just moving heat to cool a space .... with humidity you have to take the water out and the heat the water is holding ... this requires many more BTU's. In general, in humid areas you should never turn off an AC system .. you can turn it up .. but not off.

Without doing a full load calculation it's hard to know where your 12k unit fits into the calculations. Most load calculations .. don't automatically factor in a hot garage under a space -- is the floor insulated? That heat has to go someplace. Being able to drop a 90 degree room down in the heat of the day with the roof next to it may be too much for 12k BTU's

My guess is you are going to have to keep the unit on and figure out what temp works best for how you use the space -- mini's are deigned to be maintaining ..even though many times they are oversized and not used that way.