Swapping outputs on a Mitsubishi heat pump condenser to fix serial error

jakedeg

Hi Folks! First time poster here!

I bought a home with an 8-zone mini-split install. On the first floor, we have one outdoor condenser unit (Mitsubishi MXZ-4B36NA-1) powering two indoor evaporator units (Mitsubishi MSZ-GE15NA-8). One of the indoor heads is not working properly and the other is. I could provide a lot of backstory about my issues and all the troubleshooting steps I have taken both with service tech visits and on my own, but I'll spare y'all the boring details unless someone tells me it's relevant. But basically, I think I have narrowed the problem down to the specific output on the electronic control PCB in the outdoor unit.

But if I'm understanding things correctly, this MXZ-4B36NA-1 has capacity for up to four indoor heads with four serial outputs and four power outputs. I am only using two of them (1 and 2, as installed) and I think Serial Output 2 is busted. Can I swap one of my indoor heads to be driven by a different (previously unused but hopefully functional) output from the PCB?

I tried swapping the wires connecting to serial outputs 2 and 3 and it made the error lights stop on my indoor unit, and it seems to be responding to control correctly, so that was promising, but I don't think it's actually cooling the air as it should. I don't have probes to properly measure the delta T, but just by feel, this unit is not pushing out air that is as cold as its partner.

Do I have to do other things too? Do I need to swap the power leads from 2 to 3 as well? Do I need to change anything about dip-switches or settings somewhere to tell the unit to output on 3 instead of 2? Other ideas?

Thanks!

Photo of the PCB here:

ratio

Yes and no. You can swap the wiring, but there's still the refrigerant piping that needs to be delt with. Most correct would be to move over to the correct set of refrigerant ports, however that's quite involved & might not be necessary. The last Mitsubishi multi split I worked on appeared to have a function to learn the connections & account for them. Get the service manual for your outdoor unit from mylinkdrive.com & read through it. If that's not an option, you can swap the power heads off the EEVs, which will effectively make the old ports the new ports.

pecmsg

ratio said:

Yes and no. You can swap the wiring, but there's still the refrigerant piping that needs to be delt with. Most correct would be to move over to the correct set of refrigerant ports, however that's quite involved & might not be necessary. The last Mitsubishi multi split I worked on appeared to have a function to learn the connections & account for them. Get the service manual for your outdoor unit from mylinkdrive.com & read through it. If that's not an option, you can swap the power heads off the EEVs, which will effectively make the old ports the new ports.

If you switch the EEV Heads, you'll also have to switch the sensors!

I don't think that's a correct set up for the models given.
http://www.mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10009\M_MXZ-B_Series_Multi-zone_indoor_Outdoor_Combination_Table-en.pdf

jakedeg

Interesting! Thanks for the help!

That makes sense that the living room unit is "working", but not getting cold if the condenser is trying to send refrigerant to output 3, and it's still piped to output 2. I certainly don't want to get into that plumbing project.

@ratio Can you say more about what you mean by "swap the power heads off the EEVs"? Making the old ports new ports sounds exactly like what I'm after.

And @pecmsg, Can you say what makes you think it's not a correct setup? Looking at that PDF you linked to, I do see my models listed as an "OK" combination, right? I may be misunderstanding you.



If all else fails, I guess I could buy a replacement PCB and swap it out, but it seems a shame if there are two outputs worth of perfectly good electronics sitting there unused.

ratio

Ok, you can find the manual at http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10005\M_MXZ-B~NA_SERVICE_OBH560L_2016-12.pdf. It claims to have "10-2. AUTO LINE CORRECTING <MXZ-3B24NA, MXZ-3B30NA, MXZ-4B36NA, MXZ-5B42NA> Outdoor unit has an auto line correcting function which automatically detects and corrects improper wiring or piping." on page 57. Shut the unit off for at least 5 minutes (Do wait the whole time. I've had Mitsubishis not reset fully because I wasn't waiting long enough.) Turn on the power to the outdoor unit (presumably withe the indoor units set to off), & wait one minute. After that, press SW871. The red & yellow LED will be lit & the green one flashing while it's thinking about it. Afterwards, red & green will be on & yellow off if it did its thing & all three flashing if it ran into trouble. In any case, press SW871 again to stop the function.

If that doesn't work, you can move the power head of the EEV (called LEV by Mitsubishi). Photo 7 on page 88 of the manual shows the location, they're smaller black caps, with a harness that plugs in to the control board, that fit over a stainless bulb on the copper lines that lead to the ports that go to the indoor heads. (You'll need to take the service door off to get to them, but you don't have to strip it down.) Pop the one off of the port that connects to the indoor unit & replace it with the one that corresponds to the new wiring configuration.

jakedeg

I think this worked! Rather then messing with the actual black caps, I just swaped the terminal blocks on the PCB where the control wires for the LEV caps connect to the PCB's output (at the bottom of my photo). I swapped those in the same way I had previously swapped the serial wiring and now it's getting cold again. Thanks for your help! Pointing out that I also had to swap the refrigerant control was the key!

ratio

Glad it worked (I was sure it would...)

I didn't mention swapping the plugs because they're colored & my OCD won't let me plug them in wrong.