bad compressors

Paul S_3

I have this commercial air conditioning account that I just obtained. Previous company charged tens of thousands to repair equipment but could never fix it. They have a 15 ton water cooled unit that works fine.....but in the winter they shut the cooling tower down. So they have a 10 ton 2 circuit evaporator hung on the back of the 15 ton unit using the blower Of the 15 TON unit. The condensing unit's however are air cooled through the wall.....there is (4) 2.5 ton condensers (2) 2.5 per circuit. ....these are individual condensing unit's running in tandem....all (4) compressors are faulty mechanically.....are they overheating? Poor oil return?.....can you run (2) individual condensing unit's in tandem on 1 evaporator? ....want to solve this issue once a for all for this customer thank you Paul s

ChrisJ

They fail in the winter or randomly?

I'm not the best person to ask but I suspect a drawing, even a crude one of the system may help greatly if you can supply it.

Also what refrigerant, type of compressors, do they have crank case heaters etc?

Has anyone figured out how the compressors are failing? Broke valves, seized, burned windings?

Paul S_3

Posted pic of setup. R22 refrigerant crankcase heaters...2 compressors are seized the other 2 sound like broken valves....they are Copeland ZR scroll compressors ....manufacture states a Copeland CR reciprocating.

Paul S_3

This is the only picture I have of the equipment. ...but you can see they are side by side in a closet....the other 2 sit directly on top of units in pic

pecmsg

When you say Tandem these were set up from the factory that way, Common suction and Common discharge lines? If yes then they must run together. If run separately the oil will pump out of one and not return. Also when one fails both must be replaced.

I'm also course how there piping a 15-Ton system in the summer but only using 10-Tons in the winter? Sounds like a nightmare!

Maybe this will help:

Paul S_3

Not from factory ....field installed 2.5 ton condensers teed in ......(2) 2.5 ton condensers tied in each 5 ton circuit. ....i dont think they came on at same time they have time delays on each condensing unit set at different times

pecmsg

Paul S said:

Not from factory ....field installed 2.5 ton condensers teed in ......(2) 2.5 ton condensers tied in each 5 ton circuit. ....i dont think they came on at same time they have time delays on each condensing unit set at different times

How does the oil know where to travel to? Assuming it can travel at all with the reduced velocity!

Paul S_3

Well it doesn't no oil equalization connection. ....if I wire it so everything comes on at same time and if a safety trips have all units shut off at same time would that help? If not next step 1 ten condensing unit or (2) individual 5 ton condensers for each circuit

Techman

Put in 2 5t cond units w/ headmaster,CCH, and a LLSV for pumpdown and probably a Receiver.And be aware of left over oil in the evap coil damaging the new comps. The 15t of air(CFM) might cause a problem w/ the 10t of AC. What is the application? Is humidity a concern?

Paul S_3

Are you recommending by 2 5 ton condensers with headmasters already installed or to field install them with a reciever?....I've never installed a pump down on air conditioning. ...how would I control them ? Use a general purpose relay ? Thermostats energize and de energize the coil of relay and run the LLSV through the normally open contacts? And have condensing unit's just operate on LPC'S like refrigeration. ....thank you Paul s

Paul S_3

For the oil in the evap would just a strong nitrogen purge be suffice....and then a flush with rx-11..... the application is just comfort cooling in a office space where an out 50 people work in cubicles thanks.... as far as the cfm customer stated it worked fine in the past but we all know how that goes. ..thanks Paul S

njtommy

Sounds like you adopted a problem child.
Do an acid test first.
Flush it good and change txv's install some new dryers suction side to.

I would do pump down like a normal refrigeration system no need to get fancy.

If your installing 2 new 5 ton condensers with scroll compressors you can't really pump them down, but you can use a LLSV as a stop valve to prevent migration. Also depending on brand you could see a micro channel coil which you can't pump down any way. I would stay far away from a micro channel coil especially with low ambient conditions.

unclejohn

You have a pipe size problem. You need a double riser to get the oil back. And you should have a oil separator at the condensing units.

Techman

The 10t evap is factory piped a 2-5t coils or just 1- 10t coil? .I'm not following along w/ why a LLSV & receiver cannot be pumped down and why a Scroll can't be pumped down also, and why a Micro Coil can't handle a pumpdown?

On a Nitro purge, the velocity/mass has to be high enough to push/sweep out the oil otherwise you will accomplish very little.

Then as unclejohn said , you might need a "double suction riser", depending .

Then, depending , if not a HeadMaster, then at least a MotorMaster Head Press Controller along w/ "ball bearing" cond fan motors.

njtommy

Scroll compressors aren't not recommend to be pump down do to having problems with oil leaving the compressor. Also they have no internal valves. I have read conflicting information tho.

Micro channel coils the name almost says it all. The channels are so small they have a hard time sending oil through them in low ambient conditions also they hold a lot less refrigerant so you can't stack the refrigerant in the condenser like you can with a standard copper aluminum coil. York has put out a couple memos about this.

njtommy

I've seen it a couple times where the log up and will actually bang off on high head pressure.

Techman

njtommy, Copeland says that is ok to do a LLSV pumpdown. There is a check valve inside the comp to prevent, discharge gas from backflowing into the comp, recycling the comp by the LPC. There was a time back in the early 90's when Cope eliminated the ck.valve and an external ck.valve had to be installed/added. Just don't pull into a vac.

Then if the receiver was sized correctly there will be 0 increase in the hiside press and 0 stress on those goofy micro coils.

The new comps and oil will be required to run in cold/cool outdoor temps so the Cool/Cold weather controls are a must, I think.

Thats a good thought about the cold thick oil squeezing thru the Micro Coil passages. What is the lowest outdoor temps that this AC is supposed to run at ?

Paul S_3

The evaporator is 2 5 ton circuits .....customer says they use the air conditioning all winter long ....its NYC it gets to 0f here sometimes....

ChrisJ

Paul S said:

The evaporator is 2 5 ton circuits .....customer says they use the air conditioning all winter long ....its NYC it gets to 0f here sometimes....

This may be a dumb question but wouldn't the smart move be to bring in some outside air under those conditions?

Techman

Then I stick to my guns, it gets just as cold out here in mid Suffolk County.

njtommy

Realisticly you shouldn't have to run AC under 60 degrees, but we also don't know what space there trying to cool.

@Techman if Copeland says it's ok to pump down the compressor then it's good by me. Install a LLSV and let it roll. Rather have pump down anyway.
Have you changed any micro channel coils yet?

njtommy

Crankcase heater and icm fan speed control or even a head master go along way with old weather.

ChrisJ

I run my window units when it's in the 50s and even 40s sometimes as our area gets very humid at times and often the house is warm from the sun.

But I can't imagine a building ever needing anything when it's below 30 out, at least if you can bring outside air in , no?

I'm asking because I honestly don't know and am curious how large buildings are usually set up. I always assumed some sort of damper let outside air in if the conditions were right (fairly dry, cool etc).

njtommy

Larger commercial building generally bring in outdoor air depending on the set up.
The problem with bringing in out side air is the ability to freeze chilled water coils and heating coils. Even with all the fancy controls and safety's it still happens every year we get broken coils.

ChrisJ

njtommy said:

Larger commercial building generally bring in outdoor air depending on the set up.

The problem with bringing in out side air is the ability to freeze chilled water coils and heating coils. Even with all the fancy controls and safety's it still happens every year we get broken coils.

Why not use antifreeze?

njtommy

Some systems have glycol in them, but you need to maintain the system and cheap is best. Some times you can only write it up make the customer aware of the problem. It's up to them to have you come out and fix it.
I've seen new equipment look like total crap with in a few years do to lack of maintenance and the customer not want to spend money.

Techman

I have several customer's that need AC 24/7/all year, even New Years Eve! Sorry Love , Gotta go , emergency at B. Fire District, Dispatch Rm. is warm. 0* ,wind blowing, snow driving, temp is headed to -5*F. Been there, Done that! Never, not once has my girlfriend then my fiance then wife complained.

njtommy

Techmen she is a keeper then. It's very hard to keep a work/ live balance. This trade takes over your live.