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a/c issue
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New User
Joined: Aug 2019
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a/c issue
I have a 2005 F150 and the a/c will come on by itself when I have the switch in the off position. It doesn't matter if driving or just cranking the truck if it decides to come on it will. I can turn the blower motor switch on then back off and it cuts off and it might not come on again for days ,weeks or months. Where would I start to look for trouble at.
Hotshot
Joined: Jul 2005
Posts: 11,931
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if the blower starts up with the switch in the OFF position, I would look at the switch or the resistor that sets the speed...
I think the resistor set is in the air duct under or behind the glove box. You can lay on the passenger floor and look up to see a small cube with a 4 wire harness connected to it... normally it screws to the air duct......... at least all older trucks were made that way and I assume the 2005 is similar.
I think the resistor set is in the air duct under or behind the glove box. You can lay on the passenger floor and look up to see a small cube with a 4 wire harness connected to it... normally it screws to the air duct......... at least all older trucks were made that way and I assume the 2005 is similar.
Hotshot
Joined: Jul 2005
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Hotshot
Joined: Jan 2004
Posts: 19,767
Likes: 1,082
From: St Louis
It's not the resistor. The resistor cannot create power for the circuit when power is supposed to be disconnected by the switch.
Either the blower relay is sticking closed or the EMTC module is defective. I'd give odds to it being the EMTC module.
Either the blower relay is sticking closed or the EMTC module is defective. I'd give odds to it being the EMTC module.
Fleet Mechanic
Joined: Apr 2016
Posts: 1,653
Likes: 193
Does the ac clutch come on and also the blower .There is a clutch relay on drivers fender that signals the clutch . If both the clutch and blower coming on its most likely the ac control module .The pcm overviews some of the ac controls such as pressure switches . Perhaps someone has disturbed wiring working on head unit or radio . But most likely a junk yard control unit may be a good starting point . I have some diagrams on my other computer but I have not delved into the different ac controls. I have the lariat auto control and everything is still working at 206 k . Your control must be issuing this command in my opinion at this distance .
Fleet Mechanic
Joined: Apr 2016
Posts: 1,653
Likes: 193
I know the clutch relay does not control the blower . I was just pointing to check points and explaining my guess how most systems work . If clutch and blower coming on then its most likely the ac control doing it . I really don't have enough info at this point .The pcm has a lot of overview on most of these .Since the area of the ac control is next to the audio unit it gets some unwanted attention to modifications . So many times you hear later I was putting this mod on and then !!!! But not a word about it until much later . But boy have I seen some wiring backfeed disasters.
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Logistics Pro
Joined: Jan 2001
Posts: 3,740
Likes: 37
From: Central NYS
The 1&done original poster said that the “a/c” comes on by it self.
I assume he is referring to the a/c compressor.
Doesn’t the PCM cycle the a/c compressor when the starter first starts to crank the engine?
I don’t know, but I *think* I read that someplace.
I assume he is referring to the a/c compressor.
Doesn’t the PCM cycle the a/c compressor when the starter first starts to crank the engine?
I don’t know, but I *think* I read that someplace.
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Hotshot
Joined: Jan 2004
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From: St Louis
The WSM describes it as follows (from the '05 F150 manual):
Compressor Anti-Slugging Strategy
Liquid refrigerant may accumulate in the A/C compressor under certain conditions. To alleviate damage to the A/C compressor, compressor anti-slugging strategy (CASS) is utilized.
CASS is initiated only under specific conditions:
Liquid refrigerant may accumulate in the A/C compressor under certain conditions. To alleviate damage to the A/C compressor, compressor anti-slugging strategy (CASS) is utilized.
CASS is initiated only under specific conditions:
- the ignition is off for more than 8 hours
- the ambient temperature is above -4°C (25°F)
- battery voltage is above 8.5 volts during engine cranking