Understanding VRF's

[marc5180]

I was called to a job this week where i found a Mitsubishi Electric VRF short of gas. I reclaimed the remaining refrigerant and found the leaks and repaired them. Then put the system under pressure/leak test and then vacced the system out. The standing charge was 21kg and the additional was 13.7kg. I managed to get 25kg in through the vacuum and then i turned on the system to try and get the remaining 9.7kg in, this is where i didn't understand the workings of it.

I put the contollers (11 of them) on test cooling, then the system ran up on the inverter compressor. I got another 5kg in and the suction came down to 4 bar and the discharge went up to 18bar It didn't switch over to the fixed speed compressor?? it stayed running on the inverter compressor. The 2nd fan was running very slowly But was giving air off 35DegC.

Inside the temperature was coming down slowly and we had temperatures of around, 15/16 deg C, then all of sudden as i was stood at the condensor, it just stopped. I checked all the controllers and they were still on test. Then after 5 minutes the compressor came back on but the pressure was sp 6 bar and dp 10 bar, the suction was warm. Then both condensor fans came on at full speed and ran for a few mins but all the time the pressures stayed the same. I checked the indoor air temps and was getting 18degC, went back outside and found the pressures still at 6 bar and 10 bar and not moving.

I know its temps not pressure that i should be looking at but i'm working on these more and more and im finding them very hard to understand. The pressures and temps always seem to go against what i have been taught and i don't know why:confused:

[Thermatech]

Mark

R410a City Multi systems have a set procedure to carry out for the first 3/4 hr operation from any 3 ph power up.
You cannot override.
During this time the system will not ramp up to max performance & will stop / start without warning.

A lot of time can be saved if you get all the refrigerant charge into the system before start up.

If you get the refrigerant cylinders really warm & have a good vac you should get it all in.

Or use your refrigerant recovery rig to pump it in. Just take some common sense precautions for safety & ensure recovery rig is not contaminated with acid oil from the burnt out compressor job it was used for last time.

If you start with a full charge you can let the system do its stuff while you have a cuppa & chat up the receptionist.
Then after about 3/4 hr you should see the outdoor unit ramp right up provided you have a good heat load in the building.

[marc5180]

Thanks for that thermatech. It cleared things up a little:D

[IPASA]

Also you have to charge only liquid in R410a, not gas like R22. If you charge gas, you must have to charge again liquid, because R410a have two kind of refrigerant and when you charge liquid you don´t have problems, but when you charge gas, you don´t know how many percent of each, and this make problems like in your situation.

Regards...

[sinewave]

I think he might just know that basic fundamental of charging! :D