Heat pump pumping down

[furnacemaninc]

I have a 10ton trane r22 rooftop heat pump package unit that has two five ton comps splitting the capacity. I replaced a burnt out compressor yesterday, new filter dryer added suction dryer, replaced outdoor coil txv due to a damaged sensing bulb line that had a hole rubbed in it, weighted in the charge. Tested the unit in cooling and the suction side pumped down in about 20 seconds discharge was at 150, there was no drop across the suction dryer. I shifted the unit into heat and the unit ran well with 13' sh and 15' sc. I reclaimed r22 and inspected indoor metering device piston and found no restriction or screen. Inspected check valve with a magnet and could hear it move. Recharged unit and found frosting at check valve in cooling mode. Do you think I can have a restricted check valve even though it move? Could there be a screen before the check valve?

[BBeerme]

Recharged unit and found frosting at check valve in cooling mode. Do you think I can have a restricted check valve even though it move? Could there be a screen before the check valve?

Don't know about a screen, never cut one open. But if that check valve is supposed to be open in the cooling mode, and it is frosting (and assuming the proper charge), then I'd be looking there for sure. If it is supposed to be open for cooling, you could even cut it out for troubleshooting; depending on how fast you need to get the system on line. Just be sure to follow up. At an absolute minimum, you'd then want to disable the heating and tag the system as such.

[manny238]

I'm pretty sure those check valves have screens in them.

[skpkey9]

Don't know about a screen, never cut one open. But if that check valve is supposed to be open in the cooling mode, and it is frosting (and assuming the proper charge), then I'd be looking there for sure. If it is supposed to be open for cooling, you could even cut it out for troubleshooting; depending on how fast you need to get the system on line. Just be sure to follow up. At an absolute minimum, you'd then want to disable the heating and tag the system as such.

In cooling the evap check valve is closed, and yes there is a screen.
It's possible ball is not seating properly causing frosting. For temporary repair, crimp check valve body with pinch off tool and replace check valve.

Hope thi s helps...

[Makinhole]

If the check valve is restricted in the indoor unit, how does that make the suction pressure pump down? That would just ensure the refrigerant flows through the indoor metering device.
By the way hello, neighbor!
However if frosting is happening anywhere I would replace the restricted component.
Hopefully the "suction dryer" is by-flow, or else it will stop flow in one direction.
Also check that the suction service valve is open.
Hoping nitrogen was flowing while brazing was going on.
If the check valve that is frosting up is in the outdoor unit, it should be open in cooling, but is directing the flow of refrigerant through the metering device, then I could see the suction pressure going down. However in that case I would expect to see higher head than the 150 listed.
My suspicion points mostly to the lack of a by-flow dryer or the suction dryer.
Good luck, keep us posted.

[just_opinion]

Your problem is at outdoor.
Trane normally uses x-valve on both inside and outside next to the txv. Hopefully you did not remove the old x-valve when you changed the old txv.

By the way one-way drier won't get clogged like other posted. There is NO check valve inside the single way flow drier. It is just that the desiccants can burst and got into the system.

[Home&Marine]

I'm pretty sure those check valves have screens in them.

Yes They Do. And... when the screen is full of trash they trap oil. Know what happens when you remove them with a torch? You can be caught on fire with Hot Flaming Oil. (I have the scars.) The way Trane designed the circuit, if there's trash in the system it will get Caught in the check valve screens. I have added a FD up stream and resolved the problems with trash/check valves. You can normally tell by the temps if they are restricted. I have some new ones on the truck... don't know that I want to go find them for show & tell but...

Reading your post again, add the Filter Dryer in front of the New Check valves and save yourself some trouble.

[manny238]

Yes They Do. And... when the screen is full of trash they trap oil. Know what happens when you remove them with a torch? You can be caught on fire with Hot Flaming Oil. (I have the scars.) The way Trane designed the circuit, if there's trash in the system it will get Caught in the check valve screens. I have added a FD up stream and resolved the problems with trash/check valves. You can normally tell by the temps if they are restricted. I have some new ones on the truck... don't know that I want to go find them for show & tell but...

Reading your post again, add the Filter Dryer in front of the New Check valves and save yourself some trouble.

Yeah I try to make it a habit to replace the check valves and driers if I have any suspicion of a restriction.......Especially on those Carrier package heat pumps with the header metering device.

[furnacemaninc]

In cooling the evap check valve is closed, and yes there is a screen.
It's possible ball is not seating properly causing frosting. For temporary repair, crimp check valve body with pinch off tool and replace check valve.

Hope thi s helps...

The check valve is piped in parallel with the outdoor coil txv, the indoor coil uses a fixed orfice, suction dryer was piped in between the compressor and the reversing valve, unit m# wsc120a4roa1

[furnacemaninc]

Thanks for all the help, I'll give an update after the repair is completed