Evacuating a Danfoss compressor with low pressure port only?

[daifu]

I want to evacuate my fridge system as I'm 99% sure there's moisture in the system (cools quickly then: gurgling sound from the evaporator stops; evaporator warms up; low pressure drops to <=0 psi; compressor still running; cools again once warmed up and gurgling sound starts)

The only problem is I only have a low pressure service port.

Any known issues with evacuating the system from just the low pressure port?

I assume it will just take longer as the high pressure side has to equalise with the vacuum in the low pressure side?

[zaphod]

You can evacuate through just the low side with no problem.

It does sound like there may be moisture in the system, but the question is, how did it get there? Have you opened up the system or recharged it in the past? If so, did you repair the leak? Do you have a refrigeration grade vacuum pump and a micron gauge? Evacuating to remove moisture only works if you are able to pull a deep enough vacuum to vaporize the water.

If you have the skillset you should consider brazing in a filter/drier on the liquid line. You can even get one that has a high side schraeder port.

Supco D111 Copper Drier a.co/d/eVrG0yR

[daifu]

Thanks Zaphod,
I'm pretty sure the moisture got in when i was trying to top up the gas a few weeks ago - I forgot to purge the lines before adding gas

I do have a hvac grade vacuum pump and gauges but not the brazing skils (yet). There is a filter/dryer already there (pretty old). The filter/dryer you linked to looks like it has a built-in port - good to know they exist, and I'll see if I can get someone to fit one.

In the meantime I'll try leaving the vacuum on for a while and warming the filter/dryer, evaporator and lines, to get as much moisture out as I can and see where we go from there.

Cheers

[daifu]

Update:

It worked! I evacuated the system using just the low pressure port. I had to leave the vacuum pump on for a good 30-40 minutes until the vacuum stayed at -30" when I disconnected it.

If I disconnected before this, the vacuum decreased slowly (pressure increased). Initially, I thought it must be a leak but I knew it had held gas for several months before hand - I then realised it could just be the remaining liquid boiling off and creating some pressure, so I vacuumed some more.

Once evacuated, I slowly filled with aircon gas bought from Halfords, and eventually (after several hours of slowly filling with 5 second squirts, then waiting 10 minutes!), the pressure stabilised around 10psi.
The evaporator measured -20C and the fridge box dropped to 1-2C with no frost on the return lines :-)
Success!!

I think it may still be little undercharged but will check it again in a few days after leaving it off for 2 days.

Cheers