5 Zone Mitsubishi Mini Split Problems

toolman32

Here's my current set up:
MXZ-5C42NAHZ2-U1 Outdoor Unit
PAC-MKA52BC 5 port branch box
5 indoor units: Three (3) MSZ-FH09NA Wall Mount, Two (2) MFZ-KJ09NA-U1 Floor Mount

I installed this system for a customer in January 2021 and have seem to have intermittent problems from the beginning.

Current Problem: In cooling mode, all 5 head units will run for about 30 min, then one Floor Mount indoor head will give 14x flashes. During this 30 min run time, the one floor indoor head will never blow COLD air. It will blow air, just not cold air. All other four heads will blow COLD air. Go to the branch box, the lineset from the one floor mount head not cold at all. If I run the four other head units and leave the problem floor mount unit off, system will run for weeks on end with no problems. Customer claims floor mount unit runs perfectly fine in heat mode, only problem is in cooling mode.

Preface: I have already replaced the branch box on this system because I had problems with another indoor head unit, this time is was a wall mount head unit. Problem was in heat and cooling mode.

I'm at a loss! I have spent so much time at the customer's house and so much time on the phone with local distributor tech support. I'm not getting anywhere and the customer isn't happy. HELP!

GW

Wow that’s major time- working on a bb system. You’re a million % sure you didn’t pinch a refer line? 1000% sure you addressed the dips and dials? One small flub and your have issues- been there. 100% sure you added the correct gas on the initial start up? 

This would kill you in time but you could swap out an indoor unit and see if the problem goes or stays 

Ironman

How did you calculate the additional charge and how much was added? Did you remove all of the refrigerant and weigh it back in when the BB was replaced or just pump it down?

toolman32

Ironman said:

How did you calculate the additional charge and how much was added? Did you remove all of the refrigerant and weigh it back in when the BB was replaced or just pump it down?

Territorial Sales Manager calculated additional charge via his software. This was based on total length of 3/8" and 1/4" linesets and total indoor capacity. Total came to 18lbs 5oz.
Yes, weighed it back in when BB was replaced. Although, I was 1 1/2 pounds short when it was pulled out.
Only having issues with one head each time. Never multiple heads screwing up at one time.

toolman32

GW said:

Wow that’s major time- working on a bb system. You’re a million % sure you didn’t pinch a refer line? 1000% sure you addressed the dips and dials? One small flub and your have issues- been there. 100% sure you added the correct gas on the initial start up? 

This would kill you in time but you could swap out an indoor unit and see if the problem goes or stays 

No, I'm not a million % sure a refer line isn't pinched. But that should be easy to check. Also, not 1000% sure about the dips and dials. Had some help on that and he was very quick addressing them. Yes, correct gas was added on initial start up.

tim smith

sounds like if you were 1.5 lbs short when pulled out, there is a leak.

pecmsg

toolman32 said:

How did you calculate the additional charge and how much was added? Did you remove all of the refrigerant and weigh it back in when the BB was replaced or just pump it down?

Territorial Sales Manager calculated additional charge via his software. This was based on total length of 3/8" and 1/4" linesets and total indoor capacity. Total came to 18lbs 5oz. Yes, weighed it back in when BB was replaced. Although, I was 1 1/2 pounds short when it was pulled out. Only having issues with one head each time. Never multiple heads screwing up at one time.

Was the leak found and repaired?

GW

1.5 pounds short- only gonna get you in heating mode. Anyway hope the problem is resolved