Help with Mini Split Debug
Can anyone help with debug of a mini split problem ?
MSZ-FE18NA/MUZ-FE18NA, Single Head, Hyper Heat
I have had a long list of frustrating experiences with local service folks over the years. After one $400 Mitsubishi “diamond star” service call that failed to resolve the problem, I am resolved to at least have some idea of what the issue is before having another tech out.
Here are the symptoms:
Compressor runs. Inside air handler runs. Front panel lights show that the unit is active and heating/cooling. The air coming out of the air handler is the same temperature as the air going into the air handler (no cooling or heating happening).
In AC mode, the liquid connection (the small tube) gets very cold (frosts up) while the suction connection (the larger tube) remains at ambient temperature.
In heat mode, the suction connection (the larger tube) gets very hot while the liquid connection (the small tube) remains at ambient temperature.
I have to assume that this is the result of a stuck valve or lack of actuating voltage to a valve but which valve and what can I do to verify that this is what is actually going on ?
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Replies
https://www.mitsubishitechinfo.ca/sites/default/files/SH_MSZ-FE09_18NA_OBH542B.pdf
Dunno if there is anything in there that might help
Replacement pair is around $3k shipped, so might limit repair options
BTW, in 14 years the only failure I have had among 3 was very similar, both units operating, no hot or cold air, no blinking lights
It was low on refrigerant, tightened a fitting, all good for years since
Did you get a diagnosis of the problem for $400?
What does the work order say they did?
Consider disputing the CC charge.
Are the tubes still hot and cold when they get to the indoor unit?
Did they check the pressures?
Seems to me the tubes would not be getting hot or cold as described unless some refrigerant was flowing and that disproves your assumed faults.
Most likely failure is always a leak and the symptom you described sounds consistent with a leak and low charge.
Walta
You are low in gas
Thanks.
I should not have speculated about the cause of the problem in my initial post. It is quite feasible that the unit has a leak.
Is there anything else I can do myself in in terms of diagnosis to help increase confidence that a leak is in fact the problem and rule out other potential issues ?
About 99% chance it is a leak. Since you still have some pressure in the system, you can start with soap bubble test over the flare fittings at the outdoor unit and the indoor head.
The only other thing it could be is a kinked line. Very unlikely as you would have noticed it right after the install.
Sorry you have such trust issues with your technician. Is it just this one or all of them?
A system leak is the most common reason systems get replaced. Finding some leaks borders on impossible others are obvious. Fixing some leak is as simple as tightening a fitting other require aluminum welding almost impossible skill for most humans.
The only way to be certain a system has a leak is to recover the charge and weigh it and compare it to the specifications for your unit. All that required training and equipment.
Walta