Runing high head pressure!

[todouble]

Ive got a Copeland C8AJ0200CAV001 condensing unit and its conected to an existing Treton evap coil. We replaced the condenser with a new one, changing the txv, drier, and sightglass. We've done over 100 of these that we have all over the area and this one for some odd reason is running high head pressure and tripping out. Existing unit was a R-12 with AB oil and the new one is R-22 with POE oil. The condenser fans are turning up to speed and in the right direction, the coils are brand new, the refrigerant charge is correct, we got the vacumn down to 200 microns on the original install and put in virgin refrigerant. Thoughts of non-condensables in there, so we removed refrigerant, changed drier again and installed again new virgin refrigerant. Suction is running high as well. We are looking for a 40 degree evap, the space is cool (75 degrees). There is an identical unit right next to this one that is running normal with the same refrigerant and same amount in it. Doesnt make sense, any ideas???

[genesis]

Whats the super heat? Sounds like a bad head on the TXV if you have identical units if you have ruled out a restriction

[jim2005]

Yes what is the super heat and what is the sub-cooling. Are you sure it is not overcharged. Are you stacking refrigerant.
If it is overcharged and has a liquid restriction you will see high head pressure.
I tell my guys to do a start up sheet on the equipment and after they gather all not just some of the needed info, they find the problem right away.

Good luck

[cy]

are you sure existing evaporator coils are completely clean?

Ive got a Copeland C8AJ0200CAV001 condensing unit and its conected to an existing Treton evap coil.

[icemeister]

Is it tripping out on the high pressure control or the overload protection?

What were the suction & discharge pressures, the box temperature and the ambient temperature when it tripped?

At a 40ºF evaporator temp and 90ºF ambient, this unit should run close to 300 psig discharge pressure. If your evap temp and/or the ambient is much higher you can get to the trip point real easy.

[todouble]

Generally restrictions give me low suction and thats what has me hungup. I have higher suction than normal, along with my high head pressure as if theres a huge load to work with. But the space temp is normal at 75 degrees. Ive replaced the txv and drier again and still have same problem. The evap and cond coils are squeaky clean and were positive the charge is right. On the original startup which I completely myself things were running excellent and everything was normal. This problem just came about wirh some higher than normal ambient condition were having right now. But again I gave the same unit about 1 year older running right next to it just fine.

[todouble]

Also I cant keep the thing running long enough to even capture a stabilized superheat or subcooling reading. Anythibg internal to the compressor that would cause this. Bad discharge valves maybe?? I dont know much about the internal parts, but it is a semi-hermetic so we can tear apart some things.

[todouble]

Pressures are 100/375 then it cuts out. Only runs for maybe 5-10 seconds then trips hp ctrl. Box temp is at 75 degrees which is the normal setpoint.

[3rdgenhvac]

How many microns did you pull it down to???

Sounds like non-condensibles to me.

[3rdgenhvac]

sry, i just read your whole first entry, u should have no problem @ 200 microns

Probly just the initial load w/ the hot day.

[jim2005]

If it wont run long enough to check it out have you tried using water over the condenser coil or removing some of the gas.
I would fist try the water if you are certain about the charge.
And
Does this have a headmaster?

[icemeister]

Pressures are 100/375 then it cuts out. Only runs for maybe 5-10 seconds then trips hp ctrl. Box temp is at 75 degrees which is the normal setpoint.

That condition puts you solidly outside the operating envelope for this unit. That's why it's tripping out on you.....it's overloaded.

You need to add a CPR valve and set it either to the RLA of the compressor or to about 76 psig which will limit your suction to an equivalent 45ºF evap...which is where this puppy tops out.

[todouble]

We have been installing these things since 1995 and have installed over 250 of these units and none of them have cpr valves. Every other one runs just fine and this particular one is not any different tha the rest of them.

[hands]

Did you make sure the discharge service valve on the compressor is fully open?

[todouble]

Yes discharge, liquid line, and suction valves are open.

[icemeister]

We have been installing these things since 1995 and have installed over 250 of these units and none of them have cpr valves. Every other one runs just fine and this particular one is not any different tha the rest of them.

Then all I can say is that there is something about this particular system that is different from the 250 others.

From the info you gave, this unit is doing exactly what it should do at those conditions.

You have to limit the suction loading on this unit to prevent the overload trips. Perhaps all of the other system you speak of have undersized TEV's?

I dunno, I'm just going on what's given here.

[icemeister]

My only suggestion other than the CPR is to double-check that TEV to see if it's doing what it's supposed to do.

The compressor appears to be OK to me.

[jackt]

Whats your compressor amperage look like? I know this sounds stupid but, have you rechecked the compressor model number to be sure its the correct compressor for your application? It sounds like you have covered everything else. Its very rare but I have seen units come from factories with wrong compressors. It sounds like you just may not have enough HP for the amount of btu/hr

[todouble]

Well I may have to give it a shot and install a cpr valve. At this point im not sure what else to do. I have to take care of the problem for my customer, so I cant just walk away at this point. Copeland tech support doesnt answer phones or return calls either. Got word that they may be sending my call to India anyway!! Thanks for all the help, I appreciate it!! And yes I have ran the compressor numbers with the condensing unit numbers and they match up. Thanks though...

[superandy]

There may be a problem with the manufacturing of this condensing unit such as a blockage on the discharge line. Can you check the pressure on the liquid line to see if there is a huge difference between there and the compressor discharge?