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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8499
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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What would cause a newly installed unit to have 250 psi on

Customer Question

what would cause a newly installed unit to have 250 psi on the low and high side? the new unit came prefilled with the new410a gas-could it be that the lines weren't put to vacuum long enough or the unit came with to much Freon? The low side pipe seem to get pretty wet almost like the unit is starting to freeze up and the drain tank seems to fill up fairly quick (but it was 95 today in ct) thx
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Are you saying pressures are equalized? Did you open service valves?

Customer: replied 1 year ago.
Expert:  airheatman replied 1 year ago.

Can you hear compressor running?

Customer: replied 1 year ago.
u can call me up to 11-or tomorrow 12-1 or 5-7pm-thx
Customer: replied 1 year ago.
the system works but the low side seems to have excessive moisture dripping on the line and the fan/condenser doesn't seem to release hot air from fan
Expert:  Phil replied 1 year ago.

Hello, the low side will sweat (that means have excessive moisture) when the system is running, that is its job, to take moisture out of the air.

The 250 pounds pressure on both sides of the system happens when the compressor is not running and the pressures equalize... that pressure will vary depending on the weather,

Summary, if your system is running and cooling the house and the suction line is sweating, the system is working perfectly... do not mess with it,

Use a liquid liquid leak detector solution on all of the tube connections to insure that none are leaking...look very very closely at the connection for any sign of a bubble that is growing.

If your system is working properly, and it is, we know that because the suction line is sweating, the air coming off of the condenser is as warm as it should be, only 10 or 15 degrees warmer than the outside air.

Please rate my work here, and I will call you between 12 and 1 your time, but you must tell me which time zone you are in.

To rate my work, locate the 'Finish and Rate' link and click on it, Thanks!

Customer: replied 1 year ago.
Thanks, ***** ***** that. The new assembly I replaced came precharged, and I later found that one of my gauges was leaking a bit which did not enable a full vacuum charge and I released the gas into the system and found that both pressures are very high-low side 225 and high side 315. I am assuming since it still probably had air in system and I opened the precharged condenser valve that this is the reason why pressures are so high? Should I just do an evacuation and recharge or do you think there is another issue?
Expert:  Phil replied 1 year ago.


Run the system in cooling mode for 1 hour when it is hot outside, then tell me the *exact* outside air temperature... and the **high side pressure.... exactly.

Then within 5 minutes of taking those readings, tell me the **exact return air temperature at the cooling coil (that is room temperature), then tell me the **exact temperature of the cold air being blown into the room by putting the thermometer **1 inch inside of the cold air discharge grill.

It is very important that you use the *same thermometer* for all of these temperature reads (and also NOT an infra-red thermometer).

We can go from there