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Etienne
04-01-2007, 04:21 PM
This is my first entry so let me first say hi to all of you. I've been reading a few post here and I've found some valuable info and for that I want to thank you!

I am working on a freezer running on 404a and I have a few problems. When the unit turns into defrost mode, the suction side pressure doesn't change, it stays at the same pressure as when the compressor is running (10-11 PSIG, which I know is too low for 404 but that's another issue). Can anybody give me a clue as to what to investigate because I don't think this is a normal situation!

Thanks for the help!
NH3LVR
04-01-2007, 04:53 PM
Welcome to the Forum Etienne!
We need to know a bit more about your system.
Number of Evaporators, type and size of Compressor, Type of defrost, etc.
Just on the face of it it sounds like it is not going into defrost mode.
Is the Evaporator Icing up?
Etienne
04-01-2007, 06:33 PM
I've resolved the defrost issue.

Compressor is a 1/2HP semi-hermetic, 1 evap, tx valve, receiver and defrost is done by heating elements.

Now I'm worried about the charge of refrigerant. A suction pressure of 11 PSIG is too low for 404a but since the sight glass is full, I am assuming that the system is not undercharged. Now how can I make sure I have the right charge? Do I just put gas up until I have an appropriate suction pressure?
davej
04-01-2007, 08:55 PM
Hi etienne,
are you sure that the sight glass is full, it is possible that when short of gas there is so little in the glass it is easy to assume its full, i would suggest you check its is full by pumping it down and when you reopen the receiver valve watch the glass to see the amount of liquid.
nh3wizard
04-01-2007, 09:10 PM
What was the defrost issue?
Etienne
04-01-2007, 10:08 PM
What was the defrost issue?

a broken relay, simply!
Peter_1
05-01-2007, 06:48 AM
If the problem was always there: too small an orifice, evaporator too small, compressor too big.

If happened just recently: TXV partially blocked due to moisture or TXV is loosing it's charge.
But, most important measurement for this: what's your SH?

Don't search much further for the moment.