[Mark_B]

I recently left a startup troubleshoot. Here are some details:

Mitsubishi PUMY-060 outdoor unit connected to several Mitsubishi indoor units. The original call was a "No AC" call. Our tech showed up, found the LED display in the PUMY showing error code 4100 - "Compressor current interruption (Locked compressor)." Our tech then diagnosed a bad compressor via "a bad winding" and a bad power board (not sure how power board was determined).

We replaced both components, only to find the same problem present itself at startup - compressor drawing locked rotor amps, no start. The tech doing that startup checked the compressor and found it grounded. Thinking it was a bad compressor from the factory, that tech ordered another compressor.

The second replacement compressor was then installed and also didn't start. Again, error code 4100. That tech began troubleshooting, and determined the power board was bad, leaving the following notes: "Checked compressor and wire connections from circuit boards and voltages. Found compressor windings, wire connections, and voltages are good except inverter output. Inverter output to compressor is bad due to voltage cutout during demand."

I went to replace the power board. Compressor still failed to start. I found the compressor grounded and measured amp draw of 25A during the brief period it did try to start. LRA for this unit was listed at 21A, RLA at 19A. At one point the compressor even shook around some while trying to start. Error code 4100 arrived again. I wasn't able to find any misconnected wires. I checked the compressor terminal with a megger and found the windings grounded. I did not order another replacement compressor, need to return to troubleshoot.

Where would you look to find the problem at this point?

 

[gustavhorna]

you probably didn't evac the unit properly

 

[Mark_B]

you probably didn't evac the unit properly

I highly doubt a sub-par evacuation would cause immediate failure. Further, the gentleman who evacuated it is very thorough and experienced.

 

[Mark_B]

you probably didn't evac the unit properly

Although I am doubting it, I am curious your reasoning for thinking this

 

[TechmanTery]

The CSR comp terminals mis-wired from the factory? Is the LL service valve not opened? What is the comp start up voltage at the comp terminals?

 

[BNME8EZ]

How old is this unit. Was this the original start up or has it ran in both heat and cool.

 

[Snapperhead]

Locked Rotor is 21 and running 19 ? Thats a very small gap

I've never worked on Inverter

Are they DC volts ?

 

[hvacvegas]

you probably didn't evac the unit properly

Ive taken compressors and ran them open to the atmosphere, snd even dumped water into the suction and it still ran for days before failing.

 

[hvacvegas]

When you say inverter/power board.

Are you talking about the board with the dip switches that the condenser motors tie into, or the other board?

When you checked it to ground, did you check it wires unplugged from the compressor?
Depending on what position the triac gates are in, you can get a dead short to ground through the inverter.

Waa the compressor checked prior to install?

 

[hvacker]

Ive taken compressors and ran them open to the atmosphere, snd even dumped water into the suction and it still ran for days before failing.

I remember a couple guys that missed diagnosed a compressor. In warranty. Not exactly ethical but Like you they ran it pen to the atmosphere. For hours. Finally overheated enough to ground.
These thing don't die EZ.
It should be expected as there is no load.

I had a contractor call to check his install of a mini with no cooling.
His guys never opened the valves. It ran for two weeks before I arrived.
These units are able to run under very bad circumstances.

 

[hvacvegas]

I remember a couple guys that missed diagnosed a compressor. In warranty. Not exactly ethical but Like you they ran it pen to the atmosphere. For hours. Finally overheated enough to ground.
These thing don't die EZ.
It should be expected as there is no load.

I had a contractor call to check his install of a mini with no cooling.
His guys never opened the valves. It ran for two weeks before I arrived.
These units are able to run under very bad circumstances.

We did it if it had unit replacement on compressor failure.
Price for a unit swap was cheaper than a reversing valve.

 

[gustavhorna]

Although I am doubting it, I am curious your reasoning for thinking this

as easy as that: if you have 3 compressors fail in a row, then _you_ are doing something wrong.

 

[pecmsg]

as easy as that: if you have 3 compressors fail in a row, then _you_ are doing something wrong.

Prior to the EPA getting involved we rarely evacuated..............Blast a little R-12 through the pipping and good to go!

 

[TechmanTery]

Prior to the EPA getting involved we rarely evacuated..............Blast a little R-12 through the pipping and good to go!

LOL X2.
Hook up the freon drum to the LL and open the drum and SWEEP OUT all of those nasty NCG's thru the other end of the open LL.

 

[hvacstress]

What is the voltage going to compressor terminals / compressor must be off line /voltage must be balanced , Output voltage must be 50 - 130 V .[FONT=&quot]All 3 phases to each other and then to ground.[/FONT][FONT=&quot][/FONT]

 

[Mark_B]

The CSR comp terminals mis-wired from the factory? Is the LL service valve not opened? What is the comp start up voltage at the comp terminals?

LL service valve is open. Terminals were wired correctly, based on diagram, at the terminals. However I need to check connection at the power board.

I will check the voltage next time.

 

[Mark_B]

Locked Rotor is 21 and running 19 ? Thats a very small gap

I've never worked on Inverter

Are they DC volts ?

I agree its a small gap. I'm not sure if DC or AC.

 

[Mark_B]

When you say inverter/power board.

Are you talking about the board with the dip switches that the condenser motors tie into, or the other board?

When you checked it to ground, did you check it wires unplugged from the compressor?
Depending on what position the triac gates are in, you can get a dead short to ground through the inverter.

Waa the compressor checked prior to install?

Im talking the board that directly powers the compressor.

Yeah, wires were disconnected when checking for ground.

The compressor was regrettably not checked.

 

[Mark_B]

What is the voltage going to compressor terminals / compressor must be off line /voltage must be balanced , Output voltage must be 50 - 130 V .[FONT="]All 3 phases to each other and then to ground.[/FONT][/SIZE][/COLOR][SIZE=1][FONT="][/FONT]

I will check next time. Thank you.

 

[Mark_B]

How old is this unit. Was this the original start up or has it ran in both heat and cool.

Unit about 6 years old? I doubt it has run on heat mode but I cant be sure.