Mitsu City Multi - Possible LEV Issue In Heat Mode

System condenser is PUHY-P96TKMU with two PEFY-P48NMHU-E air handlers. Each AH has a local PAR30MA controller. It's been in operation for about two years or so.

For a couple of months, they constantly complained that one area, where AH2 is situated, is constantly warm at times despite setting the thermostat well below indicated room temperature. I finally spent some time trying to isolate where the excess heat is coming from as they utilize multiple other units on the same floor. I was certain a duct from another system was broken in the ceiling.....

I turned AH2 off on the thermostat and went up to open the control box. I noticed the suction line was blazing hot despite the unit being turned off. I opened the coil and condensate pan access panels and confirmed the evaporator coils were extremely hot. If I turn off AH1 via the thermostat, the evaporator on AH2 cools down quickly. Turning AH1 back on with AH2 in the off position, AH2 starts pumping out heat again.

Things that I have checked so far with the limited time I had.

- Confirmed M-Net communication cables are in the correct terminals

- Confirmed local controllers are in the correct terminals

- Checked all units for proper addressing

- Checked for error codes (None)

- Piping appears to look good.

- Disabled the 4 degree temperature compensator garbage via DIP SW3-8

- Set DIP SW1-1 to utilize internal thermostat sensor



I did a visual inspection of the LEV and the control head seems to be tight and the harness is firmly seated into the board. No knocking or abnormal sounds coming from the valve as the service manual indicated. I didn't have time to check the resistance of the valve head yet.

Since this is the first time I've encountered this issue, the service manual stated to check the pulse output of the board with an LED check tool? I can't find this thing anywhere. I suppose I could use a DC multimeter instead as it showed the valve receives 15 VDC? Wouldn't the system throw a code if the valve is shorted or has an open circuit? I suppose the valve body itself could be mechanically jammed into the open position.

I didn't find anywhere in the service manual about "resynching" the LEVs. Could this possibly be the issue and if so, what is the correct procedure?

I have to go there next week for some other maintenance work and allotted more time to try and diagnose the issue. Kind of a real head scratcher.

Pull the power head off the lev when you do that it will go to full open, providing the actual valve is not faulty You can then start it up and see if you get some cooling do not run the unit with the head off for any extended period of time.

Quote:

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Originally Posted by hvacr1

Pull the power head off the lev when you do that it will go to full open, providing the actual valve is not faulty You can then start it up and see if you get some cooling do not run the unit with the head off for any extended period of time.

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If I unscrew the powerhead on the LEV it should allow the valve to mechanically open to the full position if it's working properly? I assume in heat mode, it should get hot faster since the powerhead is removed and flow is unrestricted.

It would be great if I can isolate the issue to the powerhead or indoor board since changing out the LEV would be a nightmare.

if your removing the lev head, use 2 open ended spanners, and dont remove the head fully as they can be a bugger to get back on- think its a 14,17mm spanner, get a service manual for the outdoor unit, read via sw1 dipswitches valve position, sensor values, resistance values for sensor is marked on indoor unit wiring diagram

I went back to this job today.

I connected to M-Net via the maintenance tool. I also powered down the system for 10 minutes before connecting.


With the system powered on and not running, I have 120 Pulses on the suspect air handler. I then checked the LEV setting on the other air handler which is also set at 120 Pulses.

If I call for heat on the first air handler, you can see the LEV pulses fluctuate. On the second air handler and no call for heat the LEV remains at 120 pulses and bleeds refrigerant through. You can also see the liquid and gas pipe thermistor temperatures rise.

While the system is running on heat and the second air handler functioning normally, I manually set the LEV on the first air handler down to 41. You can audibly hear the refrigerant flow slow down. It seems like the valve head is functioning as it responds to inputs from the tool.

I thought I read somewhere the default position of the LEV with the air handler on and the thermostat in the off position, it should be 41?

For some reason, both LEVs default to 120. Is this right? If not, can I reset the valve with the fix release button?

double post

LEVs should shut to 41 pulses however they sometimes open slightly more when an oil scavenger cycle is being undertaken.
It does sound like your LEV is being told to stay open for some reason. Did you look at the subcooling value on the maintenance tool across the exchanger?
Have you tried running both in cooling? Does the same thing happen.
What about TH1, TH2 and TH3 are all of these reading correct?
Finally, you've confirmed no crossed m-net cables/addressing issues and these have their own individual addresses so aren't run as a single unit?
If so then;

Try a valve reset on the LEV which will re sync the valve head.
Run in cool mode and monitor the superheat across both exchangers.

Come back and tell is your results

I've tried resetting the valves by disconnecting the M-Net from the outdoor unit and powering cycling the indoor units with no luck. I went over the transmission cables again and can say with confidence they're correct. We've been in an unusual deep freeze here for the past week so I didn't bother trying to run it in cooling mode.

I went back there today to collect some data and took some screenshots. I can't see anything wrong other than both indoor LEVs remaining at 130 pulses on a no call or idle. The only thing I found wrong was a loose choke coil on the inverter wiring which didn't do anything as far as operation is concerned.

Attachment 11972

Here the system is powered with no call. Notice the LEVs remain open at 130 pulses.

Attachment 11973

This shot is after about 30 minutes running all units in test run heat mode. The valves appear to be functioning normally.

Attachment 11974

This shot is of the system still running in heat test mode, but AH 002 is stopped. Notice the LEV position is at 130 pulses and TH3 is at 123.4F

Attachment 11975

The system is still running in heat test mode, but fan mode is activated on AH002. The LEV position goes down to 110 pulses and TH3 at 110F.


Really stumped.

What happens if you shut down ahu 1 but keep AHU 2 running? What does AHU 1 Lev go to? Does it stop the refrigerant flow through the coil.

Your monitoring data doesn't show anything obvious so I wonder if it's a dip switch setting or something that's been programmed into the system.

Are the AHUs interlocked with the Mitsubishi system correctly?
Finally what interface are you using on the AHU to connect the Mitsubishi units to and have you checked all dips witches are correct?

No, the valve positions are identical on both AHUs if stopped. In other words, the issue will happen on either AHU. This kinda leads me to believe something in the outdoor unit is causing the issue.

Screenshot #3 shows that AH2 defaults to 130 pulses in the off (stopped) position while AH1 continues to run in test heat mode while modulating the valve to various positions (normal). You can see that AH2 is still flowing evidenced by the thermistor readings. You can also hear it.

Yeah, they're interlocked correctly. I'm using PAR-30 MA controllers, one on each AHU.

I checked the dip switch settings on both AHUs, but just did a once over on the outdoor unit switches. Perhaps I should double check them as well.

It's probably something so stupid staring me in the face. I started a support ticket with Mitsubishi since I'm out of ideas.

Hey mate where do you get the m-tool and how much is it ?

You should be able to get it from your Mitsu distributor (Part #CMS-MNG-E) . It only works with City-Multi and not with M & P series equipment.

Cheers mate, how does it work is it like the daikin service checker or just a cable and software? Il give them a call tomorrow and see how much it is

Yeah, it comes with an interface module with a cable that you connect to the M-Net via alligator clips. You then connect the interface to your PC via a USB cable. You can get the software from here:

http://usa.mylinkdrive.com/categorie...show/2110.html

I'm not sure if anything is different (including software) for Europe. I don't think it is, but you might want to check before laying out the money.

You have to go on a course here (£1000) and also have to attend both CMPT1 and CMPT2 courses before the M-NET one. Then it's a yearly subscription fee for the software. Normally have to be a business partner or accredited installer and spend a lot with them/know the right person to get a chance to go on the course. It's not something they advertise on their website.

Cheers mate. I'll have A word with our project team. I know we are a partner :)

Should be fine then, just got to tick the boxes on the other course :)

You can use your RDF fund for the courses too.

The City Multi heat pump system has correct operation.

All heat pump systems with multiple indoor units have standard heating mode oil return control strategy to prevent backup of liquid refrigerant & oil at any indoor unit which is not calling for heating operation.
Any indoor units not heating will close LEV to a default small opening to bleed any back up of liquid refrigerant & oil in the indoor unit coil back to common liquid line.

If the manufacturer did not include this safety control strategy & closed the indoor unit LEV to fully closed position for any unit not heating then the outdoor unit would pump hot gas & oil into the indoor coil which would condense to liquid & would be trapped at the indoor coil due to closed LEV. The system would be running short of refrigerant due to the storage of liquid refrigerant at the indoor units not heating & potentially running the compressor low on oil.
For example if there were 10 indoor units & only the last one on the refrigeration pipe line was actually calling for heating then the 9 indoor units not calling for heating would all fill up with liquid refrigerant & oil.

All manufactures of heat pumps with multiple indoor units have this type of control strategy.

Heat Recovery / City Multi PURY system has BC box hot gas solenoid valve at each port which stops hot gas flow to the indoor unit & therefore indoor unit can fully close the LEV to 41 no trapped refrigerant / no oil return problem.

Thermatech, you're correct. When I sent Mitsubishi the data, they claimed the system is running normally. They had me enable dip switch SW3-7 to see what happens. It effectively closes the TXV but still opens it sporadically to allow some return.

I'm still testing to see if the space is still overheating.