Mitsubishi Heat Pump question

gary7770

Currently working on a MXZ-8C48NAHZ hyper heat untit attached to 2 branch boxes with 7 heads ranging in size from 6k to 18k.

When turning a 6k head on for heating, it takes roughly 20 minutes for the head to start producing any noticible heat and for the fan on the indoor unit to start ramping up. The outdoor unit is the same with a slow ramp up of the fan speed.

I've found that the indoor unit in heating mode will not ramp up the fan until the coil gets hot enough to blow warm air however I though that the outdoor unit would initially work harder to meet demand and then ramp down.

Anyone have any ideas or thoughts?

Thanks,
Gary

ratio

It's a 'feature' to keep the IDF off until the coil is warmed up. It may be adjustable, but that'd be a call to tech support. Dunno about the slow to ramp up, 20 minutes seems a little excessive.<p><p>FWIW, Mitsubishi tech support has been very helpful, AFAIK they'll talk to anyone, homeowner or otherwise.

pecmsg

the fan should be on within minutes.

How old is this system?

What service has been performed.

gary7770

The system is coming up on 3 years old. There have been quite a large number of calls on this system since it was installed. The latest call was to run a new lineset to an 18k unit that previously had a 3/8" instead of a 1/2" and move it from the 3 port branch to the 5 port using the 1/2" port.

After the move, the addressing on the branches boxes wasn't updated and comm failures everywhere. Tech comes out and updates the addressing on the 5 to reflect the additional unit connected but didn't update the address ranges on the box. So they had to come back and try again, they attempted something from the outside unit instead of the branch boxes with no luck (obviously). So they came back a 3rd time and brought a tech from Peirce Phelps, he fixed the address range issues but at the end of the visit after observing the extremely long ramp up time said it appeared to be working correctly.

So on a system that was previously heating that room in 5-7 minutes it now takes 20 to even start moving the temp and another 20+ for the indoor fan to ramp up to full speed.

Something changed and I'm guessing it was the inexperienced techs at the outdoor box.

2 things that I found that could cause this issue,

1. System thinks that its running on DC current.
2. System is running in silent mode (special operations page from the install manual)

pecmsg

get a more qualified tech.

GW

https://forum.heatinghelp.com/discussion/comment/1743736#Comment_1743736

No, the fan comes on when it's nice and warm

GW

I remember the first time I had to address these dips on a Branch Box system, I wasn't thrilled at all. The Japanese to English isn't very good. The rep walked me through it. If too much time passes, i need to look at my notes. But normally I can set the dips with basic memory.

pecmsg

that coil should be above room temperature within a minute. 2 at the most. Now it might be slow but still moving air.

GW

no—-have you worked on (residential) larger multi-zone units? From a dead start, 5 minutes seems normal. I've agonized even longer on some jobs. The computers do their thing at their own pace. IF other zones are already firing, then yes, a minute or two

GW

gary7770 just one unit is slow, or all of them? if just one, need to check the dc signals. If allof them, you have some real issues.

pecmsg

I've done a few and admit never really timed it. Energize heat and a few minutes the fans running.

Big Ed_4

Good Luck ,

GW

right on, the big Double Fan units are kinda slow. But 20 minutes, something is wrong

yellowdog

if the original installers ran 3/8 to an 18k head, i can only imagine what other installation errors that there are. i wonder if they split the lineset correctly to each branch box?

gary7770

https://forum.heatinghelp.com/discussion/comment/1743941#Comment_1743941

I'll check some other units today.

https://forum.heatinghelp.com/discussion/comment/1743998#Comment_1743998

Its been an adventure for sure, adventure of the nightmare kind.

Thanks,

Gary

gary7770

https://forum.heatinghelp.com/discussion/comment/1743941#Comment_1743941

Tested a second unit (9k) on the other branch box and still slow heating. The indoor fan didn't ramp up until roughly the 24 minute mark

Thanks,

Gary

GW

I'd be afraid to know if they added the correct refrigerant levels. With these branch box systems, you really do need to read. There are so many variables, impossible to arm-chair-opinionate this type of thing. I agree, they "ran a 3/8 to an 18000", that's a little scary

gary7770

So, last changes that were made were running the 1/2 line to the 18k unit, moving it to the other branch box and then re-addressing the branch boxes.

For the outside unit, it says that SW2-2 is the Connection Information Clear Switch that you flip with the power off when "When relocating units or connecting additional units." which is basically what was done. I'm assuming that information gets stored in non-volitile memory and thats the necessity for that switch.

So my question is, after flipping that switch how long should I power up the system for before shutting it down and putting the switch back to the default position?

Thanks,
Gary

gary7770

Re: "I'd be afraid to know if they added the correct refrigerant levels"

This system ran for close to 3 years with the wrong charge. After the initial install, they came back no less than 3 times to add more not knowing that they needed to calculate the correct charge which was ultimately a total of 22.65 as reported by the Diamond System builder software that they needed someone at Peirce Phelps to run for them.

Thanks,
Gary

pecmsg

https://forum.heatinghelp.com/discussion/comment/1744213#Comment_1744213

you might want to contact a different Diamond dealer to review the entire install.

GW

When i make an error in the settings, then correct the settings, there is not any 'killing the power and waiting". I turn the system on, and that's it. Yes, it may take a few extra minutes for the computer to think about things, but no 'shut it off and wait"