View Full Version : Inverter a/c

28-11-2004, 12:38 PM
Anyone know of a method to charge an inverter a/c that is slightly short that doesn't involve reclaiming and weighing in the correct charge?

28-11-2004, 09:44 PM
how do you know it is short ?



29-11-2004, 11:03 AM
how do you know it is short ?



G'day eggs.
This question wasn't specific to one particular system.Just inverters in general.
To check if they are short of gas I run them on a forced cooling operation and most times you can see the effects of liquid boiling off before it reaches the evap.The smaller of the two pipes going to the evap will frost up.
If you run it on heating with compressor at highest speed you usually get between 15-20 degrees c between the air on and air off temps.
Sometimes the unit will come up with a compressor overload fault after a certain time of operating due to lack of cooling at the compressor.
Some Daikin units come up with a fault code when they are short.

But when you talk to Daikin they tell you that there is no way to charge an inverter system that is short,other than to reclaim the remaining charge evacuatte the system and weigh in the correct charge.
If anyone knows of a way to charge them I would be interested to know.

Karl Hofmann
29-11-2004, 11:48 AM
The inverter systems are a little like the variable displacement compressors on cars, there is no way to accurately charge by pressure, the only 100% way is to recover and weigh in the right amount...Sorry

29-11-2004, 06:52 PM
Cant you determine the right amount by monitoring the currant draw?

If all evaporators are working - full load, it should draw certain amps?

Chemi :)

04-12-2004, 12:47 PM
G'day chemi
Current draw would be too hard to charge with because other factors would influence it like ambient temps.
If you had a fully charged inverter system running at it's highest compressor speed at a certain set of ambient and room temps and you took the operating pressures.Maybe if there was a system slightly short operating at the same conditions you might be able to charge it with pressure and superheat.
Anyone buy this?
(Sounds like a long way to go about it though.)


04-12-2004, 07:34 PM
I think, but I can be wrong that you canít measure AMPS with a standard digital AMP meter (no true RMS meter) on a frequency driven motor.
The same as you canít measure voltage on the compressor side when frequency driven.
The meter is calibrated to measure AMPís on a standard frequency.
If you donít have the correct frequency, then the read-out is false.
The only thing you can do is measure the AMPís on the primary side of the inverter.

The same is true for a voltage measurement with a non- True-RMS meter.

Hey proís here, give some input about this topic because Iím not sure if this is true.


I havenít that much experience with DAIKIN VRVís Ė regular users know why- but on the Mitsubishi machines, you can diagnose the correct gas filling with the diagnostic dip switch settings on the outdoor unit. In the liquid receiver are some thermistors inserted on different heights (so different liquid levels) Those are slightly heated. If there is no liquid around the thermistor, then it will not be cooled by the liquid. The current it draws is used to measure the amount of liquid in the receiver.

If you donít have these systems, then itís not possible. Or you must evacuate all the gas, measure it and recharge it.
They donít make it easy for us. In fact a VRV or VRF is nothing more then a pack like they use in supermarkets. It can work without all that fancy electronics.
But they need to install sometimes a little bit of electronics into it to help all those cowboys who installs VRVís and especially for the young techs Ė sorry guys Ė who canít use nor read proper a manifold anymore but need a computer Ė preferable with an internet connection and a big screen, a huge hard drive, Media player on it Ö - to diagnose a compressor.
They also need it to hide faults of the system. Ever recalculated the speeds in the lines, or recalculated the speeds the manufacturer gives you? Ever recalculated the pressure losses along the lines. They do this to avoid oil migration in the system. Sloped suction lines towards the compressor. Nobody is doing it and itís seldom possible.
Many big airco systems are installed against all the rules of a good practice. And then you need electronics to solve some problems.

We installed +/- 15 years ago some sort of VRV. IN that time, VRV was the domain of DAIKIN and was VERY expensive. We installed +/- 25 ceiling cassettes of Trane. We fitted a normal expansion valve and the thermostat (remote controlled) of the indoor unit controlled a solenoid valve.
On the roof, we installed Trane condensing unit with 3 compressors: 2 x 10 HP and 15 HP. (Canít remember the exact type but it was controlled by some sort of fancy electronic controller) We removed the controller and installed a small PLC of Siemens. The only inputs we had were a common HP and LP and a simple mechanical neutral zone pressostat and the contacts of the overload devices from the compressors.
The condenser fans are controlled by a mechanical HP.
We still service this unit and the only thing that has broken in all these years are the condens pumps.
We can even change evaporating pressure ourselves. We thought even about installing two neutral zones pressostats, controlled by the outside temperature. A second one with a lower setting should control the unit during hot summer days when we experienced two years ago a little bit short of capacity.

Ever recalculated the cost if you should made yourselves a unit with 1 compressor which is frequency driven and a frequency driven fan?
They earn big money on these VRV and VRFís stuff. Thanks there are competitors on the market now like Midea, Shining,Ö