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Thread: strange inverter problem
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18-05-2006, 07:24 PM #1
strange inverter problem
got a Daikin vrv 410a which has a strange problem.
on first startup the reversing valve doesn't seem quite to have the pressure difference to kick over and gets stuck in the midway position. this sends hot gas straight into the suction line and as the inverter ramps up causes it to trip on high temp.
If I press the other two non inv's comps contactors it swaps over and holds. once away the system runs 'normally'
I now know that the system is undercharged but by only 5-8kg out of 25-28kg charge.
I wonder if anyone knows of this as it's got more than a few perplexed.
I shall be returning next week to add the final charge but in the meantime welcome any thoughts..like is the inverter ramping up sufficiently at first start up??
cheers
richard
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18-05-2006, 07:36 PM #2
Re: strange inverter problem
I find that strange as the R410a VRV units have to be put through an initial test run which will determine if the refrigerant charge is correct. As you state that the unit is under charged, this would have resulted in a failed initial run and the system would have faulted until you topped up the charge and re-tested.
How can the system run and get past the initial test with a short charge?
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18-05-2006, 08:09 PM #3
Re: strange inverter problem
Originally Posted by frank
another guy finished off and run it. it had these symptoms as i mentioned. he diagnosed a duff rev valve. then he walked. Daikin got involved and said oh he must have overheated the valve when he welded it in. oh and as you didn't install two refnets correctly we want no further contact.
This was an admission -I feel- that they had failed to correctly diagnose what was going on got confused and used the refnets as a get out..
I looked at the supposedly duff valve and it looked perfectly OK with no signs of overheating..
When I first switched the system I didn't run it in test mode as this had already been done..immeadately it run in this fault condition..
I did add additional till I run out and once up and running the system run for about 3 hours in heat -although the return from cond was 18'c and the liq inj fully on (again symptoms of short)
Cheers
Richard
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18-05-2006, 08:16 PM #4
Re: strange inverter problem
Hi Richard
In this case I would certainly want to recover the existing charge, do the liquid line calcs and then re-charge to the correct level. At least this would then rule out a charge related problem.
If the valve is then continuing to give problems you would know that the cause would lie elsewhere.
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18-05-2006, 08:24 PM #5
Re: strange inverter problem
Originally Posted by frank
due to the timescale -over one year to this point- no detailed drawings of the building works exist anymore and the fact that several people worked on the system PLUS the guy at Daikin who drew up the layout deleted his copy
At one point he said "yes it goes along there and I think it doubles back -it then goes up in a riser (boxed)"
"Oh then where?"
"don't know -I have absolutely no idea"
Therefore calcs are impossible. I spoke to Daikin and he said he would expect around 25kg for this size system and the best way would be to charge it till you get 10-12 deg temp drop at the furthest ahu.
However I shall also measure superheat on cooling and heating as a check too...
Cheers
Richard
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18-05-2006, 10:06 PM #6
Re: strange inverter problem
Therefore calcs are impossible.
OK, you may not be able to measure every single mm of liquid line length but you could do a full survey detailing each room, the kit in each room and the distance between rooms. At least it is a starting point and preferable to a "guess"
Do you know if the installed fan coils are within the index capacity of the outdoor units? Are pipework lengths within limits? was the pipework nitrogen purged during installation? - it could be that the RV is full of crap and needs additional presure to function.
Too many unanswered questions at this stage.
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18-05-2006, 10:09 PM #7
Re: strange inverter problem
Little question is this a heat recovery system? If so, does the problem happen all the time or just when the ambient temp is low? Also it should be quite simple to rule out the four way valve. If you turn off all indoor controllers the system will carry out partial pump down to collect the bulk of the liquid in the outdoor. This should ensure that you have pressure differance from high to low side, which if the four way valve is stuck in the mid position then pressures should be pretty much equal! Can you confirm if it is heat recovery and if so how old it is and if the problem is solved by turning off the controllers!
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19-05-2006, 06:02 AM #8
Re: strange inverter problem
[QUOTE]
Originally Posted by frank
Do you know if the installed fan coils are within the index capacity of the outdoor units? Are pipework lengths within limits?
was the pipework nitrogen purged during installation? - it could be that the RV is full of crap and needs additional presure to function.
However this is the third RV to have exactly the same symptoms therefore the chances of it being the valve are slim...wouldn't you agree??
Too many unanswered questions at this stage.
Cheers
Richard
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19-05-2006, 06:10 AM #9
Re: strange inverter problem
Originally Posted by puddleboy3
If so, does the problem happen all the time or just when the ambient temp is low?
Also it should be quite simple to rule out the four way valve. If you turn off all indoor controllers the system will carry out partial pump down to collect the bulk of the liquid in the outdoor. This should ensure that you have pressure differance from high to low side, which if the four way valve is stuck in the mid position then pressures should be pretty much equal!
Can you confirm if it is heat recovery and if so how old it is and if the problem is solved by turning off the controllers!
once i feel it is pretty much there charge wise I will carry out any tests anyone wants..
cheers
richard
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19-05-2006, 06:49 PM #10
Re: strange inverter problem
Well thats a new one on me, i knew of a problem with the VRV II three pipe systems. Which lets just say needed a little tweaking. When the daikin engineer attended site did he put a service checker on the system and run it in test heat/cool? Is there more than one system on the site? Why was the system ran through its test mode before the additonal charge was added?
If i was on site then i would get the rest of the refrigerant in the system and then run it trough its test mode BS5 for five seconds. Ensure that all other systems are off!
Let us know what you find! Good luck!
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19-05-2006, 06:56 PM #11
Re: strange inverter problem
Originally Posted by rbartlett
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19-05-2006, 08:31 PM #12
Re: strange inverter problem
Richard
4 Way must be either piped wrong or is of a poor design.
Me I would check the piping, if thats correct I would change the valve for a Ranco type that I know works. I have help developed some GSHP's which use reversing valves, all sorts of starting conditions with no problems.
How ever the inverter brings another possibility, two slow a minimum speed, seen it on screws, the thing runs too slow to actually do any compression.
Try possibly swapping out the borads and transducers from another unit that works to see what happens.
Maybe the unit is just too big, or it is really, really shaort of gas and ramping down quickly.
Just a few thoughts
good luck
Kind Regards. AndyIf you can't fix it leave it that no one else will:rolleyes:
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