compressor problems

[chad_nc]

I had a call this past week on a 50 ton York split system, all I was suppose to be doing was confirming a bad compressor. The compressor was bad, (mechanical failure). The customer informed me that this was the eighth compressor in four years that has gone bad on the machine (mechanical and motor failures). The machine has four Danfoss scroll compressors, a tandum on each circuit. I talked to a co-worker about this and he seems to think that Danfoss makes a shotty compressor and the only way to fix the problem is go back with all copeland compressors. The unit runs at least one compressor 24/7. The unit serves a clean room where temp. and humidity are critical. They keep the room temp at 65 degrees. Keeping the room this cold caught my eye. The unit has oil traps installed and all of the piping is correct with circuit #1 having hot gas bypass installed. Anyway I replace the old compressor and got the machine running. When it started getting the room down below 70 degrees it started bypassing the hot gas. Only circuit #1 has this, but both circuits are losing compressors. Does anyone have any input on this or an opinion on danfoss scroll compressor. Also does anyone know if cleanrooms are normally keep this cold? Any advice would be appreciated.

[Freezeking2000]

I would look really hard at floodback or oil return problems.

[ga-hvac-tech]

Your post did not say where you are, so out door temp could be an issue.

I have a chemistry lab as a customer. One room has Gas Chronographs and Mass Specs in it, and they do procedures to PPB (billions). Temp has to be 70* 24/7, with one* +/- tolerance. If the temp goes to 72*, they have to shut down the procedures.

One room about 400 SQ/FT, 3 ton RUUD pack unit, circa 1995. Unit gets taken apart and cleaned every year (Spring, coming up soon), and filters get changed every month. Had to replace low ambient kit. IMO, careful maintenance is the key to critical temp systems.

[absrbrtek]

York went back to Copelands due to the Danfoss failures. They also added crankcase heaters and discharge line check valves, this cleared up the compresser failure issues or at least put them at an acceptable level on the newer models.

If you dont already have them, add the discharge line check valves and cch's. JMHO

[jayguy]

remote condensor piping is more critical on scroll units than on recips. the scrolls do not hold nearly as much oil, so oil return is critical. check out piping, esp. if only 1 comp may be running.

[The Doctor]

on York 2006 30tonners, the copeland scroll is real in. York added a 2nd CCH to
1st stage when installing the VFD, and these also had HGB. THey also sent the installation instructions for propane kit with the parts for the VFD, but I digress. Haven't seen the Danfoss' in yorks ...

[onetime]

Copeland suggest that you change both compressors of a tandum installation, as contaminates will be in both compressors. I your first stage is running hot gas for long periods the motor is probably overheating and burning up due to lack of cool gas to cool the motor. All the prior post have good info. You may also wnat to look into how they're controlled and change the sequence and maybe add hot gas to the 1st compressor of the second tandum for more stages.