A/C Pressure Switch, Checking

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Visual check: Ensure that O-ring (color: red) 10.8mm x 1.8mm is seated in groove.

Switch function between contacts -T4a/1- and -T4a/2- (at connector housing) switches A/C Clutch -N25- off whenever:

excessive refrigerant circuit pressure is present (e.g.: insufficient air flow over condenser or if system is overcharged)
insufficient refrigerant circuit pressure is present (e.g.: when refrigerant has leaked out).

Switch function between contacts -T4a/3- and -T4a/4- (at connector housing) switches Coolant Fan -V7- to 2nd speed when refrigerant pressure rises.

Switching conditions

Fig 1: Identifying A/C Pressure Switch F129

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

Contacts -1- and -2- open below 1.2 bar (17.4 psi) and closed above 2.4 bar (34.8 psi) switching threshold
Contacts -1- and -2- open above 32 bar (464 psi) and closed below 24 bar (348 psi) switching threshold
Contacts -3- and -4- closed above 16 bar (232 psi) and open below 12.5 bar (181.2 psi) switching threshold

Switch function, checking

Fig 2: Identifying A/C Pressure Switch F129

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

-- Bridge contacts -1- and -2- with engine running. If A/C Clutch -N25- switches on, refrigerant system may be empty A/C REFRIGERANT SYSTEM, TESTING WITH PRESSURE GAUGES .