Blocked Copeland unloader valve

[sputnique]

Hi guys

I've got a recurring problem on a Copeland D4DJ-300X. I recently had to change a blocked unloader piston and the compressor went back to starting up correctly at 50 per cent of capacity load. However, only a couple of months later I've noticed that the piston must be stuck again and the compressor is starting at full capacity. The solenoid valve is working ok and I've also forced the magnetic piston but even that won't shift the valve down.

I'm resigned to opening up the cylinder head to see what's happening but can anyone recommend a work around on this for me?

[R. skiffington]

I guess you need to look a little further, find out what it is that's blocking the unloader,
When was the compressor's last oil change? Has it happened since an oil change?
The only things going through the unloader should be refrigerant and some oil (sorry, I'm sure you're aware of that) so there must be something, most probably in the oil, that's causing the blocking. Do another oil change, have a good look at the oil, look closely at the oil stainer. The answer will be there somewhere.

[Coorsman777]

I have found on a copeland comp where the unloader is on the head at an angle (4D) piston wears a grove on the bottom of the casing from the vibration causing the piston to be stuck in the closed position and not unloading the comp.

[sputnique]

Thanks for taking the time out to reply, guys.

This compressor was fairly recently retrofitted by the previous tech company from R22 to R407 so I do keep a close eye on the quality of the oil. I did a check on the oil which was ok but I haven't had a look at the strainer. I wouldn't have thought of that so thanks for that skiffington.

And thanks for the tip Coorsman777. I'm pretty sure you've hit the nail on the head. It's a twin compressor group so I've temporarily shut down the bad Copeland and I'll open her up at the beginning of next week.

So I'll keep you posted.

[Coorsman777]

Is it possible that it could be hanging up because of contamination from the POE oil and its cleansing ability?