City Multi Start Up Problems

[MOVHVAC]

I started up a Mitsi PURY234 VRF last week and seem to have a communication problem. I have started the system and all is well except four units do not show up on the maintenance tool. A bus scan shows the units but i can not monitor or start these four units. It’s driving me mad. I have exhausted my knowledge base as this is only the fourth system we have installed. There are a couple of odd things; first the four units are consecutive and the last four on the bus, second the simple MA controllers are flashing "HO". Any help would be greatly appreciated..

[Contactor]

Hi, how have you addressed the units and controllers, how have you terminated the comms wiring, what is the length of your comms wiring?

Could you supply a system layout?

Your controllers with HO are not registered to a unit / group, there's lots of reasons why this could be happening.

[Thermatech]

Check the 30v dc Mnet voltage at the indoor units.
If you have 16 or more indoor units connected to one outdoor unit / BC or very long control cable then the Mnet votage drop can too much & the Mnet voltage will be too low for effective communication at the end of the daisy chain.
The Mnet control voltage is generated at the outdoor unit & the more indoor units tagged onto the daisy chain the lower the Mnet voltage gets.
If the Mnet voltage drops down to about 26 to 27v dc then the outdoor unit & BC are unable to establish communication with those indoor units at the end of the Mnet daisy chain.
The MA controller also cannot establish communication with the indoor unit until the indoor unit has carried out its electronic hand shake with the outdoor unit & BC so it reports HO.

In this case install an Mnet voltage booster pack about half way down the daisy chain.

Double check Mnet address setting of all indoor units as they must be in the range 01 through to 50 & branch address at each indoor unit must match the refrigeration pipe connection branch / port at the BC.
Make sure to get the Mnet address correct with the SW12 for tens & SW11 for ones correct otherwise you might be setting address 61 when you realy need address 16.

[MOVHVAC]

We have checked and double checked all addressing including branch addressing for the main and sub bc. We measured 28v dc on the Mnet. Indoor units are addressed 1 through 24, outdoor unit is 51, main bc is 52 and sub bc is 63 as the first indoor unit is 13. I am concerned about the Mnet lenght. I believe the allowable lenght is around 1600 ft. If the lenght exceeds that, is that the reason why iam able to find the address but not communicate with them?

[DEVIL]

is your comm wire shielded ?, u might get interferences

[Thermatech]

When you connect monitor tool it looks at all 250 possible address locations & then does an electronic hand shake with any indoor units it finds on the Mnet network.
Indoor units = IC
Outdoor units = OC
Branch selector box = BC

PAR27 remote controllers with Mnet address work on 30v dc Mnet & are displayed at RC.
PAR21MA remote controllers do not have an Mnet address & work seperately with the indoor unit on 12v dc so they do not exist on the Mnet & cannot be monitored by the Mnet monitor tool.

When you request the Mnet monitor tool to go & find all the connected units it does exactly what the outdoor unit does when you first power it up. It looks at all 250 possible address locations & does an electronic hand shake with any units it finds on the Mnet network.
So if the Mnet monitor tool is not able to estabish communication with the last 4 indoor units then the outdoor unit will not be able to communicate with them ether.

This year I have had 2 sites when installation contractors have had this type of problem with systems with 16 indoor unit connected.
Each time there was some Mnet voltage drop.
Each time the problem was resolved by installting an Mnet booster pack.
On each site there were other identicle systems which did not have this problem however the contractors were unable to find any problem with the Mnet daisy chain control cable or connections at the units.
So installing the Mnet booster pack was an easy fix for a problem which had already consumed too much engineer time on site.

For a confirmation test why not try this.

Go to the first 6 indoor units 01 to 06.
Pull the Mnet connection off the circuit board. It normally a blue 2 pin plug & lead which comes from the M1M2 MNET terminals.
So these 6 indoor units are now disconnected from the Mnet daisy chain & the outdoor unit or Mnet monitor tool will not be able to communicate with them.
Now do a virgin restart procedure at the outdoor unit with SW2-2 to clear the connected address memory. On the second pass the outdoor unit will go to find all the indoor units now connected.
When the outdoor unit has completed this & only showing the 2 end flags on the display connect Mnet monitor tool again & see what indoor units are found.

If the Mnet monitor tool can find indoor unit 21 to 24 now but with indoor units 01 to 06 disconnected then you have proved that the Mnet system is slightly overloaded.
But also you will have proved that the last 4 indoor unit can communicate with the system & you will be able to operate them with MA remote controllers to test for correct heating cooling & branch connection test.

Based on resolving this type of problem quite a few times over the last few years I would always recomend an Mnet booster for any system over 16 indoor units & reserve the possibilty of needing one for any system with around 16 indoor units depending on the type of cable / cable lenght / number of remote controllers used.
It is very difficult to be sure when a booster might be required & when not. Quality of cable / type of cable / quality of terminal connections / total lenght of cable all could have an impact on voltage drop. So you only really find out if one is needed when the installation is complete.

You would find that the factory design engineers in Japan can calculate the voltage drop for the indoor units & remote controllers connected but would not be able to estimate for the on site conditions with the communication cable installation.

[MOVHVAC]

It was a grounding issue on the Mnet shield, the installer forgot to ground the shield at the Outdoor unit. Hooked the shield up to the ground, did a virgin restart procedure at the outdoor unit using SW2-2 (thanks for that little clue Thermatech, that will come in handy later i bet) and all was well. I assume we had noise on the shield that was not going to ground.

THANKS for all the help everyone, greatly appreciated.

[DEVIL]

yup told you shielded comm wires might be a prob, doe i sow some VRF just with unshielded simple wires and didn't had any problems, probably not going close to the power lines and short distance

[Contactor]

I had a strange conversation with Daikin a while back. Apparantly they are now telling people to use two core unscreened bell wire for comms wiring because they have had so many problems with people not using screened cable properly.

[Thermatech]

Some enginners install screened cable but dont bother to make ground connection.

The screen part of the cable is not effective against external electrical noise unless it is tagged to ground.
Mitsubishi recomend daisy chain the screen at all units on the dedicated S terminal which is just a blank terminal. Then tag the screen down to ground at the outdoor unit. Then the complete Mnet comms cable for the complete system is protected against external electrical noise.

Often they get away with it.
But if noise on the Mnet network comms cable is a problem the system normally trips on 6606 or 6607 or even 6608 faults due to poor communication.

To resolve the enginner has to remake all communication terminal connections at all the indoor units which can be a big job especially if the end user has moved in & access is not so easy.
Also doing remedial work does not look good with the enduser so its always best to get this type of issue resolved before handover.

[Daikin Yoda]

You don't need to use screened cable on VRV comms wiring. Two core un screened 1.0mm - 1.5mm

[DEVIL]

You don't need to use screened cable on VRV comms wiring. Two core un screened 1.0mm - 1.5mm

For mitsubishi VRF you do