42 PSI in an R410A compressor — is it empty?
| Posted in General Questions on
I recently had a guy come out and pump the refrigerant out of my AC compressor so I could move it. When I went to disconnect it I found that there was still pressure in the lines, I put a gauge on and it showed 42 PSI. Current outdoor temperature is 35F.
According to the EPA website the vapor pressure of R410A is 110 PSI at 35F. If there were any liquid refrigerant left in the system that should be the pressure. So all that’s in there is gas. So should I treat this system as if it is empty and vent what’s left? Of should I tell the guy to come back and get the rest?
Thanks.
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I've seen pressure build back up a bit after recovery on car A/C units. Probably similar thing happened to you, that last little bit of refrigerant is hard to get out using the recovery pump. The pressure seems low enough that at most there is a bit of gas left in the lines.
One thing to watch for is when disconnecting the linset, you should cap and shutoff all connection. On the compressor, there is the two shutoffs underneath the caps on the suction and liquid lines, close those. For the lines/head, cap the flares with proper flare plugs.
The oil in the R410 is very sensitive to moisture, you want to expose it to as little air as possible.
P.S. A bit too late, but most units have a pumpdown freature to return the refrigerant into the outdoor unit (check the manual). This avoids having to do a recovery /refill when moving the units.
Thanks. My working theory is that when the lines were vacuumed out the low pressure made the refrigerant boil, which cooled it down. At a low temperature some of it could remain liquid even at low pressure and a tiny bit of liquid was left behind. Once the temperature stabilized it would vaporize at ambient temperature. It would take only a tiny amount to reach the pressure I'm seeing. That's my theory at least.
What do the shutoff valves look like?
Remove the caps labled SH4 and SH5 (should be similar look on most mini splits):
https://www.diychatroom.com/attachments/f17/533719d1536613265-senville-minisplit-charging-procedure-minisplit.png
Underneath that there are two allen keys, turn those to shut off the the valves, it takes a number of turns to close.
Make sure to close these before disconnecting anything as this will seal the outdoor unit and you only have to vacuum the line set same as a new install when you re-connect.
Cap everything (including the valve) after you disconnect the lineset.