Fujitsu Remote Sensor: DIY Install?

[Dave-H]

Hi all -

I have a Fujitsu 15RLS3H and it's generally working well except that it's not staying on the set point as well as I'd like it to. I am pretty confident that a remote sensor would solve the problem, and I've been calling around and contacting Fujisu trying to get a price for installation.

I haven't gotten a single installer to even call me back, including the one who did the original install!

I see the parts online, and it's starting to look like a reasonable DIY. I'm not experience with HVAC, but if I 'm understanding it's just a matter of opening up the unit, plugging in the interface, doing the inside wiring, and a few command codes.

Has anyone done this job and know how tricky it might be?

thanks! Dave

 

[ford33]

You might get a better response if you told us what a model 15RLS3H was.

 

[Dave-H]

Sorry about that

It's a Fujitsu wall mounted minisplit:

http://www.fujitsugeneral.com/us/residential/products/split/wall/rls3-series/asu15rls3.html

 

[bzinsky]

The connection to the unit will likely be a piece of cake, all the wall mounted mini splits I've seen can easily be opened up while installed on the wall.

The only difficult part might be trying to get the wire from the unit to the sensor since most minisplits are installed on exterior walls and just have an opening that goes straight to the outdoors. You're obviously on your own for that one since it's just running a wire.

The part of this installation that requires hvac knowledge is a cake walk

 

[Dave-H]

Actually, the inside wiring should be a snap because I have exposed rafters and the wire can mostly be easily hidden. This is a video studio so there are plenty of wires everywhere, surface runs, etc

Looks like it'll be $250 with the interface, not too bad.

 

[Jackfre]

How high is the evaporator sitting on the wall? You may have air leakage coming through the wall influencing the t-stat bulb, which is mounted on the rt side coil on the evaporator. Find/fix that and you should not require the remote. I have a Fujitsu 15RLH2 and it is right on the money.

 

[Dave-H]

The top of the indoor unit is 92 inches from the floor, and 6 inches from the ceiling. However, it's a sloped ceiling so there is actually more clearance than that.

I checked for air leakage but it seems unlikely because it's brand new drywall and sealed up pretty well - unless you mean that it's leaking in through the hole that connects the indoor unit to the outdoor.

But if that were the case, the air that was leaking in would be colder than the interior temp, so the heat should stay on, right?

 

[Jackfre]

Yes, that is what I would assume as well. Are you getting a lot of stratification in the space? You might need a ceiling fan to reduce stratification. Call Fujitsu's tech line 888 888-3424 and discuss with them. Have your model and serial number for inside and outside units.

 

[Dave-H]

Thanks for your input.

I have a laser thermometer and have been watching the temps around the room.

With a 16 foot cathedral ceiling, there is a warm area at the very top, but it's not nearly as stratified as I thought it might be. Usually around 5 degrees warmer than the rest.

The floor is cold. It's an epoxy floor on a concrete slab - usually 5 degrees colder than the room. But, about 1 foot off the floor it warms up a lot.

To my surprise, the majority of the space in the room is within a fairly tight temperature range - not as much variation as I had feared. I have been experimenting with the fan and I am seeing that:

- if the fan is high, it cycles more. it seems that the size/shape of the room is such that more air movement winds up cycling the unit when there are still colder patches in the room

- if the fan is very low, but left on for a long time, things are much better. it seems that with the air just oozing around gently, the room slowly reaches a more uniform temp and things work better

- problem with the above is, sometimes it's cold in there and I warm to warm it up quickly, or least in less than 2 hours. if I press the powerful button, it runs for a few minutes then stops. if I turn up the fan, it runs for a few minutes then stops.

I also have a room thermometer with a remote sensor. I put the little sensor on a rafter around 14 inches above the unit. It shows temperatures that are lower than the set point, even when it cycles off.

My impression is that either the internal sensor is having trouble, i.e. it's blocked or otherwise incorrectly, that there is some configuration issue, or that the airflow is simply not good and a remote sensor could fix the issue.

I have been monitoring this one spot using the remote sensor of my little thermometer and if the unit was controlled from that point, the room would be perfect. But, that's a $400 fix so I'm apprehensive.

In this pic you can see the unit, the shape of the ceiling, and the little remote sensor on the rafter above. It sure seems to be that there is ample open space above the unit for the temperature to be fairly accurate.

Perhaps the unit is in need of repair or some other help.

 

[Jackfre]

I think you should work with the fan and continue to gather data. You have a 4 way air sweep on that unit, correct? How is it set? Prior to spending money on the unit I would have your installer back to confirm charge on the 410a. In a wide open space like yours I don't think there is much to gain from trying to fool the unit. In looking at the picture I see you have a sofa right under the unit. The unit shows you are in the heating mode. Perhaps with the air blowing right down off the unit there is obstruction of the air flow by the furniture.

 

[Dave-H]

I agree that more data is a good idea.

There is an adjustable air sweep, but it seems to move around on it's own every time I adjust it. It like to point downward when the heat is going, but yea it's sending air down towards the sofa/cabinet which isn't ideal. But, the air isn't as obstructed as it looks in that photo and rearranging the furniture isn't really an option.

If by 401a you are referring to the refrigerant, is there some reason to think that it's incorrect? When the heat is on full blast, the air coming out is in the mid 90s which I am told is normal for this kind of system.

 

[Dave-H]

Update: I had a Fujitsu certified installer come and test the unit. They found that the lines had been installed in an odd way - instead of using the compression fitting that came standard, it was cut off and soldered on. This was because the installer didn't have the correct tool and thought it would be a better seal that way, I learned later on.

We observed that for about 2 feet of line after the solder point, the line was very cold. It was suggested that there was some imperfection in the soldered seal, and probably a protrusion inside the line plus a tiny leak. The charge was not at 100%.

I had the original installer come and replace the entire interior unit, because those lines are built right into the air handler and there's no way to replace just that part.

Now, the unit works perfectly. The problem, evidently, was that without a full charge plus some obstruction in the line, the auto-sensors that manage the operation of the unit were malfunctioning.

Working just fine now!

 

[American Locomotive]

Did the original installer charge you for ruining the first unit, or did he eat the cost of a new inside unit?

 

[Dave-H]

Did the original installer charge you for ruining the first unit, or did he eat the cost of a new inside unit?

Well, the owner of the small company who did the installation seemed to have no interest in this whole matter. But, the installer replaced the inside unit out of obligation because he was the one who did the poor installation. I think he took the hit out of pocket.

 

[Jackfre]

When I represented Fujitsu I had a dealer who insisted upon brazing the joints on the evaporator rather than using the supplied flare fittings, insisting that it was superior. He had constant problems and blamed the line. I tried to keep his business, but he became very difficult. As it turned out, he changed to Mitsubishi. Some time later I saw him at a trade show and asked how the change was working out. He said, "no problems at all". I knew the Mitsubishi guy who covered his account and at the show asked him how he was doing with this contractor. "XXXX, he is XXXXdriving me crazy." Same problem! Brazing is certainly an effective method, but with the small diameter tubing the margins for error are pretty thin. Glad it worked out for you. It is really good equipment.