404a pressures in low

[Bergen D]

I have a r-404a roof-top condensing serving a walk in freezer. pressures are 235 psi head pressure and a 28psi suction pressure. Outdoor ambient is 30degress and indoor box temperature is about 20degrees. System has a head pressure control on roof for hot gas. Wondering if pressures sound right. Seems like head pressure should be lower but not sure. Was at job last week and found a 260 head pressure. Reclaimed a little bit to bring down head pressure but sight glass was still full

[2sac]

What pressure is stamped on the headmaster?

[Bergen D]

Sporlan head pressure control valve
LAC 4 215
Also found a heat exchanger about 10' from rooftop condensing unit heating up suction line with liquid line between indoor and outdoor units

[2sac]

The head is too high but not high enough to keep the suction pressure up. You need to determine why you have high head, but I don't think thats the cause of the problem. Did you get a SH reading @ the coil?

[Capz]

I think he is working on a freezer. 28psi may be a tad high for desired box temp at 0F. But I agree, check SH at evap.

[Bergen D]

Checked pressures again after box dropped from 35 degrees to 10 degrees after running for a few... 23 psi suction, 225psi head pressure. 20 degree super heat at evap coil. Total system super-heat is 40 degrees. I also have a 10 degree superheat where the liquid from the accumulator passes across the suction line, not sure what it's called but thought I would mention it. Last, the sporlan head pressure control which I believe might have something to do with it. The readings for the valve are. Hot gas inlet - 145 degrees, condenser coil liquid inlet- 42 degrees, valve outlet going to receiver than system-73 degrees. Thanks in advance.

[2sac]

Your evap SH is too high. Should be around 8 degrees with box close to temp. Is there a pressure limiting powerhead on the txv?

[Capz]

SH too high at evaporator. You are starving the evaporator. Most guys set TXV for 5 or 6 degrees at evap for a freezer. The bulb is securely wrapped and making good contact? Check this first if you haven't already.

[Bergen D]

Will return to site and check. I know bulb is making good contact because I removed bulb and heater up to check txv operation. Thanks for the help. Will check back in

[MechanicallyInclined]

Oil insulating the copper from within, where the TXV sensing bulb is located?

[jpsmith1cm]

Will return to site and check. I know bulb is making good contact because I removed bulb and heater up to check txv operation. Thanks for the help. Will check back in

What charging procedure did you use with this unit?

Units with low ambient control valves require a specific charging procedure to ensure the proper charge.

Oil insulating the copper from within, where the TXV sensing bulb is located?

Explain. This would tend to cause the opposite problem, wouldn't you think?

[trippintl0]

Checked pressures again after box dropped from 35 degrees to 10 degrees after running for a few... 23 psi suction, 225psi head pressure. 20 degree super heat at evap coil. Total system super-heat is 40 degrees. I also have a 10 degree superheat where the liquid from the accumulator passes across the suction line, not sure what it's called but thought I would mention it. Last, the sporlan head pressure control which I believe might have something to do with it. The readings for the valve are. Hot gas inlet - 145 degrees, condenser coil liquid inlet- 42 degrees, valve outlet going to receiver than system-73 degrees. Thanks in advance.

Sounds like the headmaster is working properly. The headmasters are stamped with a pressure, but that doesn't mean the system head pressure will always be exactly what that valve is rated at. I have seen 180# headmasters that bypass and maintain a 170# head and they work just fine. In your case, a 215# valve bypassing at 225# sounds just fine to me.

Yes evaporator superheat sounds high. Confirm the sightglass is clear and solid column of liquid before adjusting the TXV. Good luck!

[evilsanta]

Sounds like you are over charged to me or you have non condensibles. As far as SH 10 degrees is fine for most applications any thing lower you start getting liquid flood back

[steve wright]

I also have a 10 degree superheat where the liquid from the accumulator passes across the suction line, not sure what it's called but thought I would mention it.

Are you saying you have less superheat after the heat exchanger? Colder at the outlet of heat exchanger than the inlet?

[MechanicallyInclined]

What charging procedure did you use with this unit?

Units with low ambient control valves require a specific charging procedure to ensure the proper charge.




Explain. This would tend to cause the opposite problem, wouldn't you think?

I was talking about the possible reason for someone trying to adjust the Valve in the first place. Sorry for the confusion.

[jollygreen60]

If adding or reclaiming 404, may be "off" cause its a blend??