How do I set the cut-in and cut-out pressure on an Alco pressure switch?

Alco pressure switches have a main scale for cut-out pressure and a differential scale for cut-in. To set: (1) set the main scale to the desired cut-out pressure; (2) set the differential scale so that cut-in = cut-out + differential. For low pressure control: cut-out at 0.5 bar, differential 0.5 bar = cut-in at 1.0 bar. Use Alco's refrigerant pressure charts to convert temperature setpoints to pressures.

What does the Alco FDB filter-drier 'wet' indicator mean?

The Alco FDB sight glass/moisture indicator changes from green to yellow when the refrigerant moisture content exceeds 30 ppm for R134a or 20 ppm for R404A. A yellow indicator means the filter-drier is saturated and must be replaced immediately. If left unchecked, moisture causes acid formation, ice blockage at the expansion valve, and compressor bearing damage.

How do I select the correct Alco expansion valve for R404A?

Select an Alco TX expansion valve for R404A by: (1) calculating system capacity in kW at the operating conditions (evaporating temperature, condensing temperature); (2) selecting the valve from the Alco capacity tables for R404A; (3) matching the orifice size and external equalizer requirement (external equalizer is needed when pressure drop across evaporator exceeds 0.3 bar). Use Alco's online selector or AskWhiz for guidance.

What is the bypass orifice in an Alco solenoid valve?

Some Alco solenoid valves include a bleed orifice that allows a small refrigerant flow even when the valve is closed. This is used to equalize pressure across a compressor crankcase pressure regulator (CPR) or to allow slow pressure equalization for pump-down circuits. If a pump-down circuit is not pulling down correctly, check that you have a non-bleed valve installed in the liquid line.

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Common Alco Controls Error Codes

Yellow moisture indicator

Filter-drier saturated — replace immediately

LP trip

Low pressure cutout — check refrigerant charge and expansion valve

HP trip

High pressure cutout — check condenser and overcharge

Frequently Asked Questions — Alco Controls

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