Mitsubishi Electric VRF help

[marc5180]

We have a contact with a large firm that has a number of sites across the Uk and they are all carbon copies of each other. They all have Mitsubishi Electric VRF's which we look after but because the are all relatively new we haven't had many problems with them yet.

Just recently though when performing routine maintenance on one of the sites, one of the indoor 1 way blow cassettes wouldn't cool or heat. I switched the controller to test mode but still nothing happened. I got above the ceiling and checked the liquid going into the cassette but both pipes were ambient temperature and i couldn't feel liquid passing through. On these i would expect to feel the liquid line warm as it goes into the LEV inside the indoor unit.
All other indoor fan coils were working fine just not this one. It wasn't the last indoor on the system either

Is there a way for me to check which solonoids are open in the BC box and also if the LEV's are open or do i have to have the mitsubishi maintenance tool? Surely theres another way to check if any valves are stuck open/closed rather than keep ringing Mitsi technical?

[The Viking]

What normally happens on them is that a coil fails in the BC box.

Just disconnect the coils and compare the resistance across them.

[marc5180]

What normally happens on them is that a coil fails in the BC box.

Just disconnect the coils and compare the resistance across them.

By coil, do you mean solonoid? There isn't much if any access to the BC box, especially the top of it.

[The Viking]

By coil, do you mean solonoid? There isn't much if any access to the BC box, especially the top of it.

Yepp,

The good news is that to check you only need to get to the control box...

The bad news is that to change it you will need to go in from the top, sorry.

At some sites I looked at we have had to drop the box just to change a coil (but then we have pushed the customer to either let us relocate the box or replace all the coils in one hit)

Good luck.

[Thermatech]

For access to the B/C box with poor top entry access space try removing the bottom panel & drip tray. You get good access to all the solenoid valves.

For each port the are 3 solenoid valves A B & C.
Valves A&C are energized 240v for cooling operation.
Valve B energized for heating operation.
1/ Make sure the port address at the indoor units is correct by tracing the pipework back to the B/C. If the port address is wrong then the indoor unit will ask for the wrong port solenoid valves to open.
2/ Check 240v at the solenoid valves for that port / unplug & return plug from circuit board to confirm slovenoid valve operation by listening for the click.
3/ Run indoor unit in heat test mode with all other indoor units at off or cooling mode & then see if the hot gas arrives at the indoor unit coil. It should fill up with hot gas.
If the LEV valve is locked shut then warm liquid cannot return to B/C box & the indoor coil gradually cools back to room temp as the hot gas condenses out to liquid.
It is easier to trace the hot gas through the indoor unit coil than for cooling mode operation.

The classic mistake install enginners make is to make incorrect branch / port address at the indoor unit & dont run the units one at a time in heating & cooling to confirm the port address is actually correct.
Running all units in cooling & then heating does not prove the port address settings are the same as the pipework connections to the ports at the B/C.

[marc5180]

Thanks for the replies guys.
Thermatech- I did put it on test heat whilst all of the others were on cooling. I didn't get any hot gas through the liquid line or the coil.
Do all of the solonoids plug onto the main board? A,B and C for each port? Im sure there are 11 indoor units on this system so thats 11x3 = 33 solonoids?? Is there room?.

[sinewave]

Im sure there are 11 indoor units on this system so thats 11x3 = 33 solonoids?? Is there room?.


There'll be more than one BC box! ;)

[Thermatech]

Largest B/C box has 16 ports & 48 solenoid valves.

If you did not get any hot gas arrive at the indoor coil in heat mode then there is a fare chance the problem is incorrect branch address or solenoid valve coil problem at the box.

Check the branch address on the indoor unit & then see if the solenoids for that port energize with indoor unit in heat test.
At the same time run all the other units in cool test & see if the hot gas arrives at any other indoor unit.
If another unit get the hot gas then you know the unit is not connected to that port with the refrigeration pipework & you will need to reset the branch address to match the actual pipe connections.
If you have any unused ports on the box make sure the indoor unit is not set for an unused port.

[marc5180]

Thanks Thermatech, when i go back to the site i know what to look at. It is quite a new build so i think the problem could well be incorrect setting at the branch address but i will let you know.

[IPASA]

I recomend you to get a Mantenance Tool if you are working with this systems. Do you have any error number ?... turn on only the indoor unit with the problem and you have to wait to stop the outdoor unit 3 times, and then you will get an error number, almost times this happen because the solenoide of the LEV is broken and you have to replace. Almsot times this happen for a low voltage, check this too, to prevent that this happen in other indoor units.

[vijay_study]

Hi,

Can anyone forward link of IOM for Mitsubishi Electric VRF for cassettes.

Thanks