Ford 2003 Mustang Workshop Manual page 3070

Is the voltage reading greater than 10 volts?
C18 CHECK THE A/C CYCLING SWITCH
Key in OFF position.
Disconnect: A/C Cycling Switch C130.
NOTE: The A/C pressure cut-off switch C1078 for the
3.8L engine is shown, C1078 for the 4.6L engines is
similar. The pin locations and the circuits are identical.
Measure the resistance between A/C cycling switch
C130-2, circuit 420 (DB/YE), harness side and the A/C
high pressure cut-off switch C1078-2, circuit 420
(DB/YE), harness side.
Is the resistance less than 5 ohms?
C19 CHECK THE A/C PRESSURE CUT-OFF SWITCH
Key in OFF position.
NOTE: The A/C pressure cut-off switch C1078 for the
3.8L engine is shown, C1078 for the 4.6L engines is
similar. The pin locations and the circuits are identical.
Measure the resistance between Rotunda Breakout Box
pin 41 and A/C high pressure cut-off switch C1078-3,
circuit 198 (DG/OG), harness side.
Is the resistance less than 5 ohms?
C20 CHECK THE GROUND CIRCUIT AT THE CONSTANT
CONTROL RELAY MODULE
Key in OFF position.
Yes
INSTALL a new A/C cycling
switch. REFER to Section 412-
03 . TEST the system for
normal operation.
No
REPAIR circuit 420 (DB/YE) for
an open. TEST the system for
normal operation.
Yes
INSTALL a new A/C pressure
cut-off switch. REFER to
Section 412-03 . TEST the
system for normal operation.
No
REPAIR circuit 198 (DG/OG)
for an open. TEST the system
for normal operation.
Yes