Vent selection switch draining battery when left on.
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Vent selection switch draining battery when left on.
So the battery died in my truck this week. It's a fresh battery (like brand new as of 11/15). I went out to the truck and the battery was flat. Charged the battery up, placed a voltmeter between the negative battery terminal and ground wire. It was drawing almost 3 amps.
Next I started to pull fuses, noticed that the HVAC fuse was pulled and the voltmeter went to 0.00 amps (no radio in the car and door switch depressed), good, found the issue!
So I look over and noticed that the selector was positioned at "MIX", so I switched it to "OFF" and the amps went back to 0.00. Is this standard for these trucks? I have never owned a vehicle that required me to physically turn everything off like this. Not being lazy here but I am, at times, forgetful. I am sure many share this trait. I feel like this is more of a stuck relay issue or a grounded wire somewhere, did Ford really not de-energize the circuit with the ignition off?
Next I started to pull fuses, noticed that the HVAC fuse was pulled and the voltmeter went to 0.00 amps (no radio in the car and door switch depressed), good, found the issue!
So I look over and noticed that the selector was positioned at "MIX", so I switched it to "OFF" and the amps went back to 0.00. Is this standard for these trucks? I have never owned a vehicle that required me to physically turn everything off like this. Not being lazy here but I am, at times, forgetful. I am sure many share this trait. I feel like this is more of a stuck relay issue or a grounded wire somewhere, did Ford really not de-energize the circuit with the ignition off?
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I would love to do that but finding a wiring diagram is proving to be difficult. Many of the other forums I frequent for other projects usually have a sticky with the FSM. Is there an easy way to get ahold of a PDF or even some JPEGs of the diagrams? My google-fu isn't coming up with anything significant at the moment, either.
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Man, when I look through this forum it seems as any mention of getting a wiring diagram leads to a dead thread or noone responds. I am surprised that a community as old as this one has not provided access to its base for the information. Even finding a place to purchase a digital copy is proving difficult. I am starting to think these don't exist! lol
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Awesome, I'll keep digging. Thanks! Not trying to be impatient, just surprised at the lack of information available.
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Fleet Owner
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Thank you, yes, I do drive a 93 F150 4.9L, 5 speed. Not sure how relevant all that is. The diagram you posted says "see page 149-7 for switch testing", is there anyway you can post that image? I would assume if the ignition switch is the culprit then more things would be draining power from the system but, when I switch it to off, there is absolutely no parasitic loss according to my voltmeter.
Fleet Owner
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You assumption is wrong. The switch can be slightly out of adjustment so only a few circuits are hot in the Off position. We have seen the opposite as well....i.e. everything else works but the circuit for the starter is open in the Start position.
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I can do that, but according to the previous diagram there should be power for the blower and compressor only when the key switch is in the Accessory/Run or only Run position. IMHO your root cause is further up stream from the vent switch.
You assumption is wrong. The switch can be slightly out of adjustment so only a few circuits are hot in the Off position. We have seen the opposite as well....i.e. everything else works but the circuit for the starter is open in the Start position.
Lead Driver
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^^^^^^^ +1 both of the above. Paper FSMs, esp. the EVTM, pay for themselves.
As for the issue, see if it's the A/C compressor turning on with the MIX position. It's supposed to do that, but only with the key on ACC or RUN (why it's wired to do it with the key in ACC is beyond me, but that's Ford....). So check other components tied to the ACC position (radio, eg) and make sure they turn off with the key. It could be that the key / switch / actuator are out of adjustment so that the ACC contacts are closing with the key in the OFF position.
As for the issue, see if it's the A/C compressor turning on with the MIX position. It's supposed to do that, but only with the key on ACC or RUN (why it's wired to do it with the key in ACC is beyond me, but that's Ford....). So check other components tied to the ACC position (radio, eg) and make sure they turn off with the key. It could be that the key / switch / actuator are out of adjustment so that the ACC contacts are closing with the key in the OFF position.
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