The AC relay's pick coil is actually grounded via the Starters solenoid. One side of the pick coil goes to the yellow wire that gets 12vdc power while cranking but when not cranking that yellow wire is effectively grounded via the Start Solenoid coil because that coil is very low resistance. You need to really study the circuit and you'll see how it actually will unpick the AC relay while cranking\starting.
Looks something like this
12vdc to activate AC relay
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AC Relay pick coil
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Starter Solenoid coil
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Ground
Basically the AC Pick Coil is in series with the Starter Solenoid coil but the resistance of the Solenoid coil is significantly lower than that of the AC Pick coil so that most of the voltage is seen across the AC Pick Coil. But the minute the key hits 'START' then you have 12vdc at the top of the Solenoid coil and this now puts 12vdc on the bottom of the AC pick coil so that now you have 12vdc at both sides of the AC pick coil and that yields 0vdc across the pick coil and the relay deactivates. It's a very clever design simply based on Ohms Law of voltage drops across devices.
Try it: turn AC motor on full blast with key in 'RUN' engine off and then go to key 'START' and the AC will stop blowing. You can even measure at the AC relay or simply put your hand on it and you'll feel it click 'OFF' the minute you go to 'START'.
Quote:
Originally Posted by T77911S
cant see how it does that when the AC relay is tied to the yel wire before it goes to the solenoid.
some cars do have "unloader"relays that are tied to a contact in the solenoid that opens when you start the car.
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