carrier rtu problem

[carriertech1]

carrier 34 ton rtu, two 17 ton cicuits. Replaced A circuit compressor ran for two days and grounded. Compressor was changed again ran for 1 week and grounded. I went to the site yesterday replaced compressor. Flushed system, purged two large cylinders of nitrogen through sytem, replaced LL
drier, triple evacuated and pulled system down and held at 400 microns, charged with factory charge of 24 lbs., started unit Running 300 head, 90 suction, 20 superheat,
my main problem are my amp readings. Voltage is consistent
485, 487, 487, all wiring has been checked and ohmed out
RLA is 26.5 compressor is running at 28, 29, 32 amps fully loaded can't get amps or pressures down, any ideas?????

I just got involved on the last compressor. My SH is 20
and my subcooling is 7-9, it is a TXV system. My delta accross my evap. coil I have not taken yet I can't get the machine running propperly. My oil has been fine 1/8 to3/8


[Edited by carriertech1 on 07-07-2004 at 08:17 PM]

[klrogers]

Does it have TXV's, probably at that tonnage, if so what is the subcooling, If all coils are clean, airflow OK, I would say overcharged, don't always believe factory charge on data plate.

[bruiseandy]

how much oil did you drain out of old compressors? you should drain same amount of oil out of new compressor as you do out of old if oil charges match up. High amps probably caused by oil charge. What was your split btw?

[pincheal]

You should of done all of the steps that you took on the last compressor before you let the first compressor back into service. What were the pressures, amps, subcooling or superheat, temps, etc.. on the first one?
Generally the weighed in refrigerant listed on the nameplate are correct, but you should always do your pressure, temp. checks before leaving the site.
Use what you learned, sometimes we do this for so long that we get really complacent in our jobs, and just change parts. I've done it and it came and bit me on the a@#, don't let it happen to you.
Get back with temps, press, delta T, and whether its a TXV or Cap system in order for us to help U out.
12-14deg. superheat, 10deg subcooling should get you close to what you want. Read the post in "For your interest" in the main page and look for charging by super heat or subcooling to help you out or refresh your memory banks.

[carriertech1]

I just got on the job on the last compressor
my superheat was running 20 and my superheat at 7-9
degrees. I did not check the sight glass but my oil levels have been fine 1/8 to 3/8. I have not even got to a delta T because I have not got the unit running propperly

[bjefferson]

First thing I would like to know is what took the first compressor out?Was it grounded too?Sounds to me like either a voltage problem or a slugging problem.I would install some kind of phase monitor that reports under and over volts.Maybe a problem with the building and not with you at all.whats the oil pressure diff.?maybe your not returning oil for some reason.Although with those pressures I doubt it.non-condensables?Just some thoughts I had.

[absrbrtek]

I see no mention of a suction line drier. Did this system have acid in it? Was the oil black?

[seaboard]

Pressures are always affected by your temperatures. What was the outdoor ambient and what was the temperature split. I see that you said you didn't get to the Delta T but that is a must to know. If your return air temp is 90 degrees your pressures are going to be high. The harder the compressor is pushing (discharge), the higher the amps will be. What concerns me most is that you have not mentioned an oil sample. On that size system, you should always take an oil sample to see what clean up measures are going to be necessary. Simply purging and replacing a drier one time may not be adequate. Also, whenever you encounter a high discharge pressure take a reading of the discharge line temp as well. You are probably at a high enough temp that your oil is breaking down. I would start by cleaning the condenser coil and taking an oil sample.

[rob10]

Hi head with lo subcooling equals air flow restriction over condenser. Are the fans running in the right direction? Is the condensor dirty? Also treat this circuit as a hi acicidic burnout. Installation of changeable drier cores on both hi and lo side would be the ticket.

[Edited by rob10 on 07-07-2004 at 09:49 PM]

[trimble]

Need to know return temp, supply temp, & ambiant temp. If your ambiant and return temps are very high and your cond coil is dirty, you will overamp.

[onesidedcoin]

Whats the other circuit readings ?

[seaboard]

Originally posted by onesidedcoin
Whats the other circuit readings ?

An excellent point! Compare the two and you will know whether you have a system problem or just a problem with the one stage.

[markwolf]

You did not say weather or not you replaced the motor starter with the comp.Also you said all wires ohmed out but did you test the under load?why the high head?Are the fans all coming on as designed?Is the coil clean?There is alot of info in the carlyle handbook that might help you out too. http://www.carlylecompressor.com/PDFs/PSG/PSG.pdf