One unloader or two?

[turbo50mike]

Looking at a 25 ton replacement compressor - New compressor comes with a spot for one unloader. Existing compressor (which is a replacement, also) has two unloaders (pictured).

Carrier tech says for comfort cooling (which this is), should only require one unloader...As using two bring capacity down to ~8 tons, and oil return may be a problem if piping isn't correct (which is probably isn't for that small of a load).

What has your experience been?

[synergy]

My theory on a constant volume DX system is to run it loaded and let it cycle off on space temperature. Now if its a VAV or has multiple coils then you need unloaders.

[basprofessional]

I think unloaders are a good thing even on constant volume systems. Unloaders will reduce short cycling under lower heat loads and dehumidify the space better. However, a multiple stage thermostat is required for the extra unloader. Unfortunately, oil return is a concern and the TXV maybe affected. The TXV may not work as well when the refrigerant volume decreases to a particular level. You might have to install the unloader with some extra components or controls. You might have to install oil traps etc.

[ascj]

Looking at a 25 ton replacement compressor - New compressor comes with a spot for one unloader. Existing compressor (which is a replacement, also) has two unloaders (pictured).

Carrier tech says for comfort cooling (which this is), should only require one unloader...As using two bring capacity down to ~8 tons, and oil return may be a problem if piping isn't correct (which is probably isn't for that small of a load).

What has your experience been?

From the pic, they look like pressure unloaders. Also looks like a RTU. Is there more than one compressor?

I would keep it to one pressure unloader......if it's a single comp, constant volume rtu.

[turbo50mike]

From the pic, they look like pressure unloaders. Also looks like a RTU. Is there more than one compressor?

I would keep it to one pressure unloader......if it's a single comp, constant volume rtu.

It's a single compressor condensing unit for a single air handler.

My tech found a few other surprises...He was changing the suction filter, and found out someone had already taken it out, and not installed the retaining spring. Couldn't finish up because Irene just arrived, so time to hunker down.

He also said it looks like a piston cut loose and romped the valves. I'll have to check it on Monday (Stuck in Indy right now, and flights home are cancelled).

[basprofessional]

I think ASCJ is correct, stay with one loader because potential problems. However, I would consider the unloader if the compressor has short cycling problem. Also remember that suction dryers are only necessary if the system needs to be cleaned up. After the cleanup manufacturers recommend removing the core and installing a simple paper filter to catch the particles.

[wolfdog]

That looks like hot gas umloaders. My experience with 06D & 06E compressors is that 2 hot gas unloader heads will be problems. If you need 2 unloader heads go to suction unloaders. It is a different head.