Mini Split System prolems

[DanDMan]

I have installed A/C systems for over 20 years, but I have never worked with mini splits before and I'm a bit at a loss on my first system. I bought one for my home to see how they work before I start selling them. It worked great for a few weeks then we had a tree fall on the power line and after a extended brown out the unit seems to longer to be able to cool.

The air temp from the evaporator is 47, yet this 12,000 btu unit will not cool 448 square feet more than 3 to 5 degrees below outside temp. I have no idea how to check the inverter technology. The local ac supply house does not even sell tools. The unit is a shinco and it has no error codes and has no test button on the board. Just in case the flares leaked I recovered the unit and weighed in a fresh charge. No dice, still does not work.

I would appreciate any thought you gents might have on how to trouble shoot this!

[install monkey]

you say a tree fell on the power supply to the condenser,is the indoor unit powered off the outdoor on a 4 core cable,
is the interconnecting cable damaged , internal glass fuses on the pcb's

[DanDMan]

The tree fell on the main lines to the house. The 4 wire cable between the outside and inside is good.

[install monkey]

could the oudoor board have been zapped(sending a live up the neutral? does the indoor fan run and are u getting a cooling signal from the indoor unit and is the outdoor recieving this? if so then the fault will lie in the outdoor unit.

[monkey spanners]

I'd be looking at refrigerant charge, but you've checked that.
Air flow, coils/fliter nice and clean?
Fan blades/blower wheel clean? Have seen indoor fan wheels full of mold before.
Is it actually big enough to due the duty with the ambient conditions, temp humidity etc?
Maybe its not working as hard as it should because one of the thermistors has gone bad, so it thinks its nearer set point than it is, you'd need to check with Shinco for values etc.
I wonder if you have a frequency/Hz meter (my amp meter has a setting for Hz) you might be able to tell if the comp is running full speed or not if you can find the max frequency the inverter should put out (think some run up to 90Hz!!!)

Have a word with Shincos tech department, they should be able to help point you in the right direction too, but we don't get that make over here so i don't know for sure.

Be carefull working on the inverter wiring or boards, they can hold a fatal voltage for a few minutes even after power off!!!

If you are looking to go into the minisplit marker i would recommend one of the Japanese makers.

Jon :)

[DanDMan]

My amp meter does have a Hz counter. I have been unable to get shinco on the phone while next to the unit because I am always working during business hours :P

Think they would void my warranty if I soldered in a hi side tap so I can check the charge by sub cooling?

The filters/coil and blower wheel are clean, and the unit has only been in use for 2 months. The blower does does not seem to run as fast as it did at first, but then I might just be imagining it.

[monkey spanners]

You can't check the charge by sub cooling on mini splits, its factory charge plus and trim charge to cover long pipe run if needed.

There should be a chart with it, an example would be,

900g factory charge for upto a 5 meter pipe run, then 20g a meter upto a max run of 25 meters.

Say you have a 7 meter run, you would need to add 40grams on commissioning to cover the 2 meters over factory charge.

It may also have a minimum lenght, say 3 meters, if you are under this you would need to reduce the charge by the same 20grams a meter.

The actual values depend on manufacturer and model so you always need to check the chart in the instructions and measure the pipe run. I mark the units with any additional charge to save the next tech having to work it out again.

Air on and air off temps might help point you in the right direction.

What fan speed is the indoor unit on? Have you tried going through all the speeds in all the modes just to see if it seems right? (indoor fan fault)

I have read of a lot of people having trouble with boards with these units but they usually just stop altogether.

Does it seem to do more duty the lower you set the desired room temp? (normal inverter units ramp up the duty the futher the room temp is away from the set temp, you can here the compressor change speed)

[install monkey]

whoaa! if its precharged for 7 mtr u never remove charge if the piperun is shorter. they say on small splits a minimum piperun of 1.5mtr. i have installed units back to back with about 600mm pipe run,but the smallest charge within the system is the factory charge
You can't check the charge by sub cooling on mini splits, its factory charge plus and trim charge to cover long pipe run if needed.

There should be a chart with it, an example would be,

900g factory charge for upto a 5 meter pipe run, then 20g a meter upto a max run of 25 meters.

Say you have a 7 meter run, you would need to add 40grams on commissioning to cover the 2 meters over factory charge.

It may also have a minimum lenght, say 3 meters, if you are under this you would need to reduce the charge by the same 20grams a meter.

The actual values depend on manufacturer and model so you always need to check the chart in the instructions and measure the pipe run. I mark the units with any additional charge to save the next tech having to work it out again.

Air on and air off temps might help point you in the right direction.

What fan speed is the indoor unit on? Have you tried going through all the speeds in all the modes just to see if it seems right? (indoor fan fault)

I have read of a lot of people having trouble with boards with these units but they usually just stop altogether.

Does it seem to do more duty the lower you set the desired room temp? (normal inverter units ramp up the duty the futher the room temp is away from the set temp, you can here the compressor change speed)

[DanDMan]

So I cant charge by sub-cooling if I open up the case and tie in a tap after the condenser coil? My tester has a duty cycle option also.

[monkey spanners]

whoaa! if its precharged for 7 mtr u never remove charge if the piperun is shorter. they say on small splits a minimum piperun of 1.5mtr. i have installed units back to back with about 600mm pipe run,but the smallest charge within the system is the factory charge
This is what I was told on a manufacturers training course, they also said not to got too short or you will be able to here the refrigerant bubbling along the pipes.

I never bothered with my one at home but if I'm giving advice to others I try for to be correct as I understand it.

Jon :)

[monkey spanners]

So I cant charge by sub-cooling if I open up the case and tie in a tap after the condenser coil? My tester has a duty cycle option also.

No, the expansion device is in the outdoor unit and it will be an electronic expansion valve it's setting will be dependant on load and compressor speed and what alll the pipe temp sensors are telling the board.
The manufacturers know the required refrigerant volume for the system to work and this is the factory charge, then you may need to add more by weight depending on pipe lengths.

It's like the difference between a carb and fuel injection, each need their own ways of servicing.

Jon :)

[r.bartlett]

it's undersized

[DanDMan]

448 square feet to 1 ton, not its not undersized. Besides it worked just fine for a few weeks. Infact, it felt cold in the room.

[install monkey]

mitsi and daikin and fujitsu and panasonic or toshiba or imi dont preach that.if a system has a shorter piperun than the precharged length then the system can cope with it. installation instructions dont state modification of charge if the piperun was short. what course was it,can u remember the tutors name and did he have a ac engineering background??[ they do state a minimum piperun of 1.5mtr .QUOTE=monkey spanners;238008]This is what I was told on a manufacturers training course, they also said not to got too short or you will be able to here the refrigerant bubbling along the pipes.

I never bothered with my one at home but if I'm giving advice to others I try for to be correct as I understand it.

Jon :)[/QUOTE]

[monkey spanners]

mitsi and daikin and fujitsu and panasonic or toshiba or imi dont preach that.if a system has a shorter piperun than the precharged length then the system can cope with it. installation instructions dont state modification of charge if the piperun was short. what course was it,can u remember the tutors name and did he have a ac engineering background??

It was at LG in Slough with Graham Hendra, who seemed to know what he was on about.

Seem to remeber that i was told something similar at Fujitsu FGeurothing, but wasn't paying much attention due to low blood sugar levels caused by their poor selection of muffins and cookies at coffee break :D

We had to ask specifically rather than it being part of the general 'how to fit splits'
lesson. Its not so much it being a short pipe run but when its under the minimum allowable pipe run.
Say it will do from 5m to 15m on the factory charge, needs 30g a meter over 15m, if you have asystem that has a 1.5m run then its got 105g too much in, not sure how well grams of refrigerant convert to ml but if its even then that 105ml of liquid that has to be somewhere other than the pipe that isn't there. This would be on top of the surplus 300g that would i presume be in there to cover from 5m to 15m if the pipe run was as such.

I could well be wrong though...

Jon :D

[install monkey]

i will ask mr hendra tomorrow,maybe we should set up a poll. ive never heard of anyone removing gas. but the main question is did u get a pen!!! the food is usually crap on courses.
It was at LG in Slough with Graham Hendra, who seemed to know what he was on about.

Seem to remeber that i was told something similar at Fujitsu FGeurothing, but wasn't paying much attention due to low blood sugar levels caused by their poor selection of muffins and cookies at coffee break :D

We had to ask specifically rather than it being part of the general 'how to fit splits'
lesson. Its not so much it being a short pipe run but when its under the minimum allowable pipe run.
Say it will do from 5m to 15m on the factory charge, needs 30g a meter over 15m, if you have asystem that has a 1.5m run then its got 105g too much in, not sure how well grams of refrigerant convert to ml but if its even then that 105ml of liquid that has to be somewhere other than the pipe that isn't there. This would be on top of the surplus 300g that would i presume be in there to cover from 5m to 15m if the pipe run was as such.

I could well be wrong though...

Jon :D

[monkey spanners]

I got pens, t shirt, fleece, note pad, an inverter checker! On the few LG courses i did!

Think i got a pen and pencil and a service checker thing for vrfs on the Fujitsu course, but the coffee was rubbish, like that klix stuff you get an a plumb center....

All told they were both good courses :D

[install monkey]

so could u not get grahams pants too? or has he got stubby legs:p?

im going to e mail all technical depts over the next week to get the definitive answer regarding modifying factory charges.best hing to do with them klix machines is pull the cup out when its half full then do it again and u get off ur t*ts on strong coffee and do a 20hr shift!!
I got pens, t shirt, fleece, note pad, an inverter checker! On the few LG courses i did!

Think i got a pen and pencil and a service checker thing for vrfs on the Fujitsu course, but the coffee was rubbish, like that klix stuff you get an a plumb center....

All told they were both good courses :D

[r.bartlett]

i will ask mr hendra tomorrow,maybe we should set up a poll. ive never heard of anyone removing gas. but the main question is did u get a pen!!! the food is usually crap on courses.

I have only removed gas form some daikin wall mounts which were in a server room. piperun was 4m each and was told to remove 1kg from each by DUK tech.

http://www.refrigeration-engineer.com/forums/showthread.php?21813-Precharged-system-1-meter-run&

[Gary]

The blower does does not seem to run as fast as it did at first, but then I might just be imagining it.

No, you are not imagining it. Insufficient airflow is the problem, confirmed by the 47 degree air off temp. The evap air off temp should be 20F lower than the room temp, which I assume is considerably higher than 67F.

[Clk320_Greg]

We have been advised to remove gas by Daikin before.

[install monkey]

but when u read the installation instructions why does it not mention this???