carrier rtu

[hvacplumb]

changed out o6d compressor on a carrier mod.48tjdo16.weighed in charge of 19.3#s but was running 70 amps with fla of 61.recovered some refrigerant this is my info.l1-l2-199v,l1-l3 199, l2-l3 200v,67,62,63 amps.75#s suction,295 head pressure.20deg. s.h.,3deg. subcooling.86 return air,67 supply air backed exp valve all the way out trying to lower superheat from 30 plus degrees.ambient temp 101.i sshould have taken oil press. but didnt i have heard this particular model has had its share of factory problems such as airflow over both coils its also next to exhaust off of a tortilla oven and it serves the kitchen area.anybody have any thoughts appreciated .

[jeffcolledge]

What is your temp rise across the condenser?

[hvacplumb]

i did not check temp rise across condensor

[jeffcolledge]

Originally posted by hvacplumb
i did not check temp rise across condensor

Well, 295 with 100F amb isn't too bad I guess, what is the problem, is it not cooling or is it still over-amping?

[hvacplumb]

yes 67,62,63 on 61fla

[hvacplumb]

yes just worried about losing another compressor.

[jeffcolledge]

Originally posted by hvacplumb
yes 67,62,63 on 61fla
Right...I forgot!
go to the chat room

[seaboard]

Everything looks pretty good but it certainly never hurts to clean the condenser. Also, your line voltage is definately low which is going to cause the amps to creep up. Remember, that unit is made to operate from 208 to 240 volts. The RLA you speak of may be the rating at 230 or 240 volt. As your load drops (both outdoor and indoor temps) the amp draw should decrease also. High superheat on a hot day with a high return air temp is not unusual. You could be a tad bit low on charge. How much do you trust your scale?

[Diceman]

295 is too high, clean that pos.

[ericnyc]

did you change the compressor contacter as well?

[hvacplumb]

yes replaced contactor as well

[hvacdoctor]

Sounds silly but is the load a constant 86F return air??? Had some industrial customers using rooftops for plant that were undersized caused high superheat and overheating of compressors. Unless load comes down it might be undersized. Should get 20TD give or take on evap coil check air flows.

[R12rules]

Your amps dont look bad. Do a search on this site of RLA, FLA under the section on FYI.

Also see if there are any data charts on the performance curve for this particular compressor.

That chart(s) will tell you very clearly whether or not your unit is operating properly at the various voltages, amperages, pressures and temperatures.


Clean the pig! Bring inthe variable pressure, hi pressure washer with solutaion.

You just replaced the compressor. There is a reason that old unit died.

Your words saying it is next to a roof exhauster is evidence enough that this arrangement needs to be modified immediately!!!

A/C's and roof exhausters do NOT co-mingle well.

[twcpipes]

You are going to be overamps with a 86F return and 101 ambient. It is above unit design criteria. And you will have to wait until the space temp gets down within a reasonable temperature. The lower incoming voltage may be correctable if you can get the power company to "tap-up" the building transformer. They will balk about doing it but the "squeaky wheel gets the grease".
With all the surrounding area a/c units running it is drawing down the total area voltage especially with the high ambient. As far as the unequal amp draw, rephase the compressor T-leads until the amps get closer to each other. The imbalance really shows up when the voltage is down and the amps are high. 3 degrees of subcooling isn't bad for the 101F although when you open the TXV, it can go away. Then you have no subcooling for Net Refrigeration Effect in the cooling coils. 4-5 degrees might be better, but perhaps that's nit-picking a little unless the ambient is going to be even higher. Condenser needs to be really clean on these hot days but I suspect yours is not all that dirty.
If I may, let the unit bring the load down and then go back and recheck your readings. If the amps are still out of balance, rephase the compressor T-leads to get the a/c electrical load in more balance with the building electrical load. Could you come back with another post and let us know how this turned out.

Note: as you know, but for others, rephase is moving T1 to T2, T2 to T3, T3 to T1. You can do this twice and it may help. "Rephasing" is not "phase-changing to reverse rotation". The compressor will still rotate in the same direction by rephasing.

[hvacplumb]

we had a cool front today went back and checked unit.it is running much better.amps and superheat are good i guess it was just a combo of high load and high ambient.i think it will be okay appreciate all the input.