View Full Version : Mitsubishi VRF Problem

02-11-2007, 06:44 PM
Hi all, Been commissioning Mitsi City VRF System.
Running fine however wanted to put system on auto restart which is sw1 dip sw 9 on indoor units.
Powered off indoor and outdoor changed sw but will not work, has any body had the same problem.
have 6 indoors off 1 controller.Contacted Mitsi they say it should work, all are addresses correct.

02-11-2007, 10:02 PM
City Multi always had two standard auto restart options.

1/ SW1 no 9 setting restarts indoor units at mode they were in when power turned off. So if the units were at off mode the units will restart at off mode. If units were at on mode they will restart at on & whatever heat/cool/auto/fan the unit was working at power turned off.

The alternative auto restart is SW1 No 10 which provides forced start of indoor unit even if it was at off at power turned off.
Try it at one indoor unit & see which works best for your application & then do it on all the others. You dont need to turn off outdoor unit but you do need to turn off power to each indoor unit to reset & make them accept new dip switch settings.

Recently we have become used to making most option changes at remote controller with mode options but I still like the manual dip switch because you can always look at the circuit board & see what has been set.

The really usefull thing about City Multi is that you can use these options for cheap time clock control because all you need to do is install time clock & contactor to indoor unit power supply ring main.

Think about other typical VRV / VRF systems & you will know that if you turn 240 power off to any indoor unit the complete system stops on a fault.
This is because each indoor unit needs 240v to operate circuit board & shut down LEV valve. Therefore system has to stop as a safety precaution otherwise the one indoor unit which has 240v power turned off will allow full refrigerant bypass through that indoor unit because it was unable to shut down the LEV valve at power off.This could result in poor performance at other indoor units & potentially liquid flood back to outdoor unit when other indoor units & outdoor unit are running.

However with Mitsubishi City Multi the communication control voltage supplied by the outdoor unit to the indoor units is 30v d/c & is therefore powerfull enough for the indoor unit to use to power the LEV valve shut whenever 240v power is turned off to the indoor unit.
Other VRV / VRF systems tend to use low voltage communication control 5 to 12 v d/c & therefore need to stop complete system if 240v power is turned off at any indoor unit.

With City Multi you can turn off 240v power to any indoor unit at any time & the rest of the system continues to work normally because the indoor unit with power off will use the 30v d/c control power to shut down the LEV valve.

Not many people know that.