Mitsubishi PU-3VJC

[C_Henderson]

I have a problem with a mitsubishi PU-3VJC unit... A new compressor was installed a couple of months back, and now the unit runs fine for about two cycles after getting down to temperature and starting up again.

The third time the unit starts up, the contactor pulls in and only the fans come on with no compressor as it has gone out on its thermal overload. The fault code on the controller shows problem with outdoor unit.

I'm thinking there is a blockage in the capillary. Could someone please validate this for me if they think it is the same problem... or anything else...? Thanks

[Brian_UK]

We need some more information to answer this one I think.

Is the compressor hot to the touch ?

What are the operating pressures/temperatures?

Overheating could be due to a gas shortage, is the charge correct?

[C_Henderson]

Yes, the compressor is really hot. each time it starts up it gets hotter. i recorded the top of the compressor at around 140 degrees when it cut out the second time, this is why i think its cutting out on its thermal overload, and not starting up the third time.
And there is a correct charge of gas. each time the pressures rise a little higher... its an R22 system, running at around 35psi on the suction and before cut out on the second run at around 45psi.

[Brian_UK]

And there is a correct charge of gas. each time the pressures rise a little higher... its an R22 system, running at around 35psi on the suction and before cut out on the second run at around 45psi.

Indications are a shortage of gas with that pressure, Mitsi A/C is normally around 50+psig.
You are not getting any compressor cooling from the returning gas.

What is the superheat ?
Also a discharge pressure would be helpful if that model has a pressure test point.

[LRAC]

Hi C henderson

This may be a possibility if its a heatpump, there may be a slight chance that the reversing valve may be slightly passing gas back to the suction but without a head guage on you want know, dont let the low suction pressure fool you that the above is not happening we got caught out twice with this happening and the compressors overheated.

Regards
LRAC

[C_Henderson]

the unit isnt a heat pump, so theres no worries with the reversing valve...

im pretty sure the gas charge is fine as i put in the stated amount plus a little more as i thought the pressures were too low...

im thinkin theres a restriction or small bloackage somewhere, ei the capillary?

[rbartlett]

Hi C henderson

This may be a possibility if its a heatpump, there may be a slight chance that the reversing valve may be slightly passing gas back to the suction but without a head guage on you want know, dont let the low suction pressure fool you that the above is not happening we got caught out twice with this happening and the compressors overheated.

Regards
LRAC

I'm willing to bite on this one.

The refrigerant charge is correct by weight

so a high pressure of -say- 220 psig is leaking into a low pressure of -say- 50 psig and the result is a lower pressure of 35psig.but he shouldn't be fooled by this...

please explain the dynamics of your reasoning ...

cheers

richard

[Andy]

Hi

me tthinks the thing isn't condensing properly, but without head pressure, liquid line pressure and liquid temperature it is hard to say

But if I had to guess I would say it is a condensing problem, fan, card or control probe problem

Kind Regards Andy

PS why will engineers not fit shrider connection on the head side when changing compressors, seens to be a very common problem

[LRAC]

I'm willing to bite on this one.

The refrigerant charge is correct by weight

so a high pressure of -say- 220 psig is leaking into a low pressure of -say- 50 psig and the result is a lower pressure of 35psig.but he shouldn't be fooled by this...

please explain the dynamics of your reasoning ...

cheers

richard

Hi all
who said anything about a head preasure reading, no indication was given on any readings,if a reversing valve is stuck then no heat is being absorbed by the the indoor unit as the refrigerent is not being processed .i.e no duty in the condenser and a possibility of a complete short cycle of the circuit. The compressor would be completly cycling its own charge with the indication of the above happening.

No head pressure and no suction pressure if left to run long enough you get overheating of the compressor.

Ok i know it sounds completly wrong but here's the crunch, the refrigerent charge may have already been sitting in the evap and pipe runs and with the valve stuck the existing refrigerent will not move from its resting area if a valve is passing causing low pressures. All i can do is report on equipment history our engineers find and the faults they report.

Anything is possible if you think about it.

Regards
LRAC

[rbartlett]

Hi all
who said anything about a head preasure reading, no indication was given on any readings,if a reversing valve is stuck then no heat is being absorbed by the the indoor unit as the refrigerent is not being processed .i.e no duty in the condenser and a possibility of a complete short cycle of the circuit. The compressor would be completly cycling its own charge with the indication of the above happening.

C_Henderson-
And there is a correct charge of gas. each time the pressures rise a little higher... its an R22 system, running at around 35psi on the suction and before cut out on the second run at around 45psi.

No head pressure and no suction pressure if left to run long enough you get overheating of the compressor.

This doesn't mean anything. no suction pressure or head pressure indicates a total loss of charge that is all. A zero differential may indicate a rv fault.

Ok i know it sounds completly wrong but here's the crunch, the refrigerent charge may have already been sitting in the evap and pipe runs and with the valve stuck the existing refrigerent will not move from its resting area if a valve is passing causing low pressures. All i can do is report on equipment history our engineers find and the faults they report.

It only sounds completely wrong because it IS completely wrong.!! A bypass situation can only lead to a higher than normal operating suction pressure not a lower one.The 'refrigerant in the pipes' is nonsense as far as I'm concerned in this application.

Please scan some of your guy's reports as I'd love to read them

Anything is possible if you think about it.

Thinking something is possible doesn't actually make it so..

Cheers

richard

[wolf]

i'm noone but simple question ? when you replaced compressor did you check system with acid kit?
Did you installed suction filter drayer?

[taz24]

I think you need to go back to the basics.
Why did the first comp fail?
Was the second comp fitted correctly?
Was a correct dehumidification and gas charge take place?
Has the second comp been showing signs of failure from the start or is it getting progressivley worse?
Comp running amps, head preasure and back pressure all need logging so correct opperation can be determined.
If there is any chance that the cond fan is at fault, by pass the control and run it perminatly to rule out.
You must garentee that no air is in the system.

Good luck cheers taz.

[martin102]

what indoor unit is it?

[superswill]

just a thought OFN still in the system after 1st comp change?

[superswill]

it is from 2006 ...probaly they changed the system by now

guess we will never know,i love feedback