Hitachi Compressor in a Mammoth

[refer1]

This 6002SC-H is in a Mammoth unit M/N VVW-801-GXL

Not so much of a problem as inquiry of how to properly charge this system.
I called ACCS which they told me based on a superheat from 9-27 degrees F.

I didn't ask about what should my subcooling be at.
Just wanted to get anybody out there that might have delt with this before.

[absenceofheat]

Basically as a rule design engineers hit for 10-12 degrees of subcooling on air cooled equipment. Water cooled needs to be done on approach, however talk to Ron Shoeman with Mammoth with the data and you should get the answer you need. Remember Mammoth equipment is not cookie cutter equipment.

[rowe25]

Mammoth specs call for 5 degrees of subcooling for shell and tube condensers. I'm assuming thats what you have with that V-cube.

[emmettair]

Is this mammoth unit a standalone penthouse? Do you have anywhere from 3 to 6 (possibly stacked) Hitachi 6002SC screws with an evaporative condenser/tower? If so, i have several of them(penthouses), with 8 years of experience on those particular units. Came across many problems on both the mammoth and hitachi sides over the years. Any more ?, give me a shout.

[michael26]

emmettair, if you have the answers i have the questions. I have a mammoth unit with two screws with evaporative condenser on roof and a dx coil. I need to know how to check charge properly. I have one cicuit with 70 amps subcooling 15 degrees, superheat 30. I believe this comp has a loader valve bleeding through,this is cir 2. fla on both is 90 amps. cir 1 has 8 degrees subcooling and 35 degrees of superheat drawing 91 amps. my return air temp is 82 supply air temp is 56degrees. airflow is not a problem.

[supertek65]

emmettair, if you have the answers i have the questions. I have a mammoth unit with two screws with evaporative condenser on roof and a dx coil. I need to know how to check charge properly. I have one circuit with 70 amps sub cooling 15 degrees, superheat 30. I believe this comp has a loader valve bleeding through,this is cir 2. fla on both is 90 amps. cir 1 has 8 degrees sub cooling and 35 degrees of superheat drawing 91 amps. my return air temp is 82 supply air temp is 56degrees. airflow is not a problem.

low sub cooling, high superheat, sounds low on refrigerant or high load.
can you set your mixed air temp lower than 82? like 75.
26 degree split across the coil is also high.
91 amps is good if you are fully loaded and have about 9 degrees of compressor superheat but makes no sense because you have high super heat. check wiring, contactor. may be other reason for high amp draw!
do you have those green furnas contactors?
high split sounds like air flow. Does your mammoth run both fans at the same time?
what is your static?
most important! What is your discharge line temp and discharge superheat?
do you mean rla? compressors? or did you look at fan fla?
I have the same unit 460 v draws 90 amps when fully loaded.
something is definitely wrong!
good luck! I doubt I have helped any!
Frank

[michael26]

yes both return and supply air fans run at the same time. my mixed air temp was up due to the unit being down for awhile. the 1st cir usually run about 22 degrees superheat and 9 degrees of subcooling though, and always draws 90 amps when running loaded. the other cir acts as if it never loads. i have had a trane screw do this before do to a valve leaking through. my line set to the dx is probably 100foot long and i am checking comp superheat and not evap superheat. no i do not have furnas green contactors and i dont know why this would make the amperage higher. does 22 and 9 seem okay considering the length of the line set.

[supertek65]

Michael,
9 degrees of subcooling does seem a little low, I have exactly 12,it is like you are not backing up enough refrigerant in the condenser.
22 degrees of compressor superheat is a little high.
seems a little low on charge still.
but if you are at 90 amps then you must be fully loaded.
I bring up the contactors and connections only because it seems as if you are still a bit low on charge but have hit 100 percent rla.
if you add more refrigerant you will exceed rla.
all that said YES your superheat and subcooling are both very close to what I usually have. I think it is fine.
I also have a lot of piping,
circuit one holds 278 lbs. I still can achieve 15 degrees superheat.
I can manually load and unload with HOA on controls to check loading and unloading.
I have replaced slide valve on two hitachis , two terminal plates, re-wound motor and replaced two compressors,
Frank

[michael26]

You replaced the slide valve huh, thats impressive do you have a pdf on this. I have never seen the procedure on this. I have had problems with slide valve solenoids on trane screws before and have the test procedure for troubleshooting, but I have never replaced the slide valve. If you have any info I would definitely appreciate, I have two of these also in a dunham bush, thanks.

[jmuir]

I have changed the slide out on hitachi screws, the factory does have a test for these as well, they will send it if you ask, I found that the compressors will not stay loaded if the slide is leaking through, the amps will drop down and unload if you take power away from the load solenoid, Check charge should be at 11 degrees subcooling at 100% fla on a 90 degree day.

[supertek65]

You replaced the slide valve huh, thats impressive do you have a pdf on this. I have never seen the procedure on this. I have had problems with slide valve solenoids on trane screws before and have the test procedure for troubleshooting, but I have never replaced the slide valve. If you have any info I would definitely appreciate, I have two of these also in a dunham bush, thanks.

Michael,
I got the info from ac components, but did not keep it.
You pull the oil separator off and replace the slide valve, it is very easy.
takes about 4 hours.
not much to it.
It is way way easier than replacing a shaft seal on a york screw, that is for sure!

[emmettair]

Sorry for just now getting back with you. I havn't been been online for a while. I see there has been a few replys. Agree with some but not with others. If i can still help in any way get back with me.