City-Mult question

[RCAVH]

Hey all,
Installed a Mitsubishi City Multi about a year ago. Had to go back about a month ago found a poorly installed compression fitting and loss the charge. So after fixing the fitting pressurized/evacuated/charged. Now when we installed the system ABCO (dealer) came out and we measured the amount of liquid line and came up with 15lbs 5oz 410a. After charging it had no problems. My service manager told me that it could be short because I charged it in the cold temperature. Isn't 15lbs 5oz regardless of outside temp. Sorry so long please let me now if I'm wrong. Thanks again.

[COOLJIM]

if you weigh the refrigerant in against known installed pipe length , you should be correct , mitzy put a lot of technical information out there , i was on a mitsubishi course in boston recently and this was asked .

[dmd-marc]

I have installed a few cilty multi systems and went to numerous classes. Mitsubishi works soley on correct line sizing, then checking your charts to add the correct amount of refrigerant according to length and size. Mitsubishi has told me several time that the best way is to weight the charge in regardless of temp. Sounds like someone is referring to basic resi system where with no low ambient controls, charging is more difficult in colder temps.

[acwizard]

There is only one way to correctly know the required refrigerant charge and that is by calculating the piping and fitting per mfg instructions. Error codes and checking temperatures of the compressor shell can point one in the right direction. Checking the subcooling of the BC controller is always a good place to start.

[matttheemt]

ya there is a whole process of temp reading to charge these systems, i havent been to the classes yet but im workin on my boss, because these systems are freakin great! mixesnew rack house tech with a brand new part. can i get a hell ya in the awsome stuff thats commin out now? but anyway if you can get a copy of the class book it has a flow chart on chargeing on the fly. no guages needed.lol just a crap ton of temp readings.

[acwizard]

ya there is a whole process of temp reading to charge these systems, i havent been to the classes yet but im workin on my boss, because these systems are freakin great! mixesnew rack house tech with a brand new part. can i get a hell ya in the awsome stuff thats commin out now? but anyway if you can get a copy of the class book it has a flow chart on chargeing on the fly. no guages needed.lol just a crap ton of temp readings.

I have taken their advance service class and it is well worth the time. These units are very advanced and a mistake would be costly. You could probably sort thru the manuals but it might take a month before you even realized what Mitsubishi was even talking about.

[matttheemt]

ha ha ya i read the class book and it took till the thirddescription of how the refrig flows that i got it... the 25% heat 75% cool.lol and what the hell was up with refrig goes here resister bla does this resitor ha does that the txv. i had to start skipping that crap for now just to picture the flow. super cool though. we are gonna try to be a service comp for them. way to much potential to ignor this system

[dmd-marc]

At their service course in Chicago, their main service guy basically told us that when we walk up to the condenser for a service call, that we should be able to pinpoint the problem in 15 minutes. If not then call their service line.

[mrhvacmechanic]

As CoolJim stated,
If this was the charge at the original time of installation, it doesn't matter what the temp is like when you re-charge the system.
Just put the same amount that was first calculated.