headmasters

[aaron crimmins]

does this sound correct? 75degf ambient and head master is bypassing hot gas causing high head pressure. am i thinking correct when i say it is doing this because the headmaster is backing liquid into the condensor and putting hot gas into the reciever but the hot gas is not condensing because of the high ambient, filling the reciever with gas which takes up more volume than liquid. so the unit does not have to be overcharged to cause the high pressure when the headmaster is bad. this would be a sporlan oroa-5-180 with r-22.

[Prof Sporlan]

The OROA-5-180 is flooded head pressure control type valve. When head pressure falls below the valve's setpoint (180 psig in this case), the valve backs up liquid into the condenser which effectively eliminates some of its condensing surface, and thereby maintaining head pressure. The OROA will also bypass hot gas to the receiver when the pressure difference between hot gas pressure and receiver pressure exceeds about 15 psi. In this way, receiver pressure will be maintained when the valve is backing up liquid into the condenser.

If your condenser was sized at a 15°F TD or lower, and its pressure is being controlled at 180 psig, then one could expect some hot gas bypass to the receiver at a 75°F ambient. If hot gas bypass stops at say an 80°F ambient, you're probably ok. If not, you might be a bit short of refrigerant.

If the condensing pressure is significantly above 180 psig and you are observing hot gas bypass, then something else of interest is going on here. Two possible problems: (1) something is restricting liquid flow thru the valve; or (2) you may have a high pressure drop across the condenser coil causing the OROA to bypass all the time. If you are simply fighting with a condenser coil with a high pressure drop, you can solve the bypass problem by adding an ORD-4 differential valve in the hot gas line connecting the discharge line to the OROA.

When the OROA is bypass hot gas to the receiver, both hot gas and liquid from the condenser are being mixed in the receiver which maintains receiver pressure. But the hot gas bypass cannot occur unless there is a pressure difference between hot gas and receiver pressure.

Note that if the OROA dome has lost its charge, the valve would act little more than a tee fitting. You would see low head pressures on a cold day, and no hot gas bypass.

[Rango]

Lo heads as in what range?

[Dan]

Note that if the OROA dome has lost its charge, the valve would act little more than a tee fitting. You would see low head pressures on a cold day, and no hot gas bypass.

And what would one see on a hot day, professor?

[Prof Sporlan]

It would work properly, just like a tee...