At what pressure does the suction throttling valve's pressure differential valve open?

Per the diagram, the pressure differential valve starts to open at 10 P.S.I. and is fully open at 20 P.S.I.

What is the required suction throttle valve gauge reading at sea level?

The Pressure/Altitude Chart lists 28.5 psi (±1 psi) at 0 feet (sea level), increasing to 33.2 psi at 10,000 feet.

What adapters are needed if the gauge set hoses don't have charging valve actuating pins?

Install fitting adapters T71P-19703-S and R on the manifold gauge low and high pressure hoses.

How should the system be depressurized to avoid losing refrigerant oil?

Open the low pressure gauge valve a slight amount so refrigerant discharges slowly; after the system is nearly discharged, open the high pressure gauge valve very slowly to avoid losing an excessive amount of refrigerant oil.

What refrigerant does this system use?

The evacuating procedure calls for attaching a tank of Refrigerant-12 (R-12) and a vacuum pump to the manifold.

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Ford A/C Suction Throttling Valve Diagram & R-12 Discharge Procedure (Shop Manual)

Ford A/C suction throttling valve refrigerant flow diagram with pressure/altitude gauge chart 36-32-7

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A/C refrigerant service page showing suction throttling valve refrigerant flow plus a pressure/altitude chart of required gauge readings from sea level (23.5 psi) to 10,000 ft (33.2 psi).

AI caption June 2012 · Photo 98 of 363

This is page 36-32-7 from a Ford factory shop manual section titled 'A/C General Service—Refrigerant Systems.' The top of the page presents Figure 10, an exploded cutaway diagram of the suction throttling valve (STV) showing refrigerant flow, with callouts identifying the protection cap, regulated evaporator pressure test connector (charging valve), liquid bleed line connector, expansion valve equalizer line connection (to compressor suction pressure), and the pressure differential valve, which starts to open at 10 PSI and is fully open at 20 PSI. Flow arrows distinguish regulated refrigerant pressure (evaporator) from non-regulated refrigerant (compressor suction). Below the diagram is a Suction Throttle Valve Pressure/Altitude Chart listing required gauge readings (±1 psi) from 28.5 psi at sea level to 33.2 psi at 10,000 feet, in 1000-foot increments. The lower portion begins the 'Refrigerant Service' section with a step-by-step procedure for discharging the R-12 air conditioning system, including installing fitting adapters T71P-19703-S and R if the gauge hoses lack charging valve actuating pins, venting slowly through the low pressure gauge valve, and opening the high pressure valve slowly to avoid losing refrigerant oil. The page ends with the first two steps of 'Evacuating the System,' which call for discharging the system and attaching a Refrigerant-12 tank and vacuum pump to the manifold.

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Frequently asked questions

At what pressure does the suction throttling valve's pressure differential valve open?: Per the diagram, the pressure differential valve starts to open at 10 P.S.I. and is fully open at 20 P.S.I.
What is the required suction throttle valve gauge reading at sea level?: The Pressure/Altitude Chart lists 28.5 psi (±1 psi) at 0 feet (sea level), increasing to 33.2 psi at 10,000 feet.
What adapters are needed if the gauge set hoses don't have charging valve actuating pins?: Install fitting adapters T71P-19703-S and R on the manifold gauge low and high pressure hoses.
How should the system be depressurized to avoid losing refrigerant oil?: Open the low pressure gauge valve a slight amount so refrigerant discharges slowly; after the system is nearly discharged, open the high pressure gauge valve very slowly to avoid losing an excessive amount of refrigerant oil.
What refrigerant does this system use?: The evacuating procedure calls for attaching a tank of Refrigerant-12 (R-12) and a vacuum pump to the manifold.