AC Relay Stuck ON

[bigfootchiro]

Hey guys! Long time since I posted asking for advice. Just as the title says, my AC relay, per the scanner data, shows that the AC relay is being commanded ON at all times. No matter if I unplug all sensors, unplug relay switch in engine fuse box, swapped out blower resistor motor and all, played with climate controls, etc, it stays ON. I believe that’s what’s causing me from moving forward with the crank relearn process. Any ideas guys?
@swathdiver @east302

 

[Doubeleive]

Hey guys! Long time since I posted asking for advice. Just as the title says, my AC relay, per the scanner data, shows that the AC relay is being commanded ON at all times. No matter if I unplug all sensors, unplug relay switch in engine fuse box, swapped out blower resistor motor and all, played with climate controls, etc, it stays ON. I believe that’s what’s causing me from moving forward with the crank relearn process. Any ideas guys?
@swathdiver @east302

is it shorted? have you checked for voltage to the relay?

 

[bigfootchiro]

is it shorted? have you checked for voltage to the relay?

i swapped a relay in that I knew was good and it did the same thing. Haven’t checked for voltage to it though. Would a short cause it to default to ON?

 

[swathdiver]

@UmmScott @SnowDrifter @gpracer1

 

[Doubeleive]

i swapped a relay in that I knew was good and it did the same thing. Haven’t checked for voltage to it though. Would a short cause it to default to ON?

It's a possibility, only one way to find out, sounds like you tried all the other possibilities

 

[bigfootchiro]

It's a possibility, only one way to find out, sounds like you tried all the other possibilities

Thank you! I’ll give that a shot and find out

 

[UmmScott]

Disconnect the HVAC control head and retest..
Problem goes away = bad control head
Thats an easy somewhat quick test.

If it still is being commanded on, gonna have to look at the wiring diagram. Can remember if its a power or ground side switched relay.

When does the clutch engage/come on? Is it on when the ignition is on? Or is there a delay after starting the truck and then it comes on?
There's 2 signals to watch for...
Ac command on signal and the actual ac output from The PCM.
If you have an AC request signal present then the PCM is going to activate the ac clutch relay.
Gotta figure out if there is a programming issue causing this or if its a hard fault in the PCM or even a crossed/shorted wire.

If your scan tool is saying there IS an AC request, then something electrically in a module is malfunctioning for some reason. If you have the HVAC control head unplugged then there shouldn't be an AC request at all im pretty sure of that

Sent from my SM-G975U using Tapatalk

 

[bigfootchiro]

Disconnect the HVAC control head and retest..
Problem goes away = bad control head
Thats an easy somewhat quick test.

If it still is being commanded on, gonna have to look at the wiring diagram. Can remember if its a power or ground side switched relay.

When does the clutch engage/come on? Is it on when the ignition is on? Or is there a delay after starting the truck and then it comes on?
There's 2 signals to watch for...
Ac command on signal and the actual ac output from The PCM.
If you have an AC request signal present then the PCM is going to activate the ac clutch relay.
Gotta figure out if there is a programming issue causing this or if its a hard fault in the PCM or even a crossed/shorted wire.

If your scan tool is saying there IS an AC request, then something electrically in a module is malfunctioning for some reason. If you have the HVAC control head unplugged then there shouldn't be an AC request at all im pretty sure of that

Sent from my SM-G975U using Tapatalk

thanks for the reply! Yes, I disconnected the HVAC controls and still get the AC relay request ON. I can’t remember when it comes on. I want to say the compressor has a delay, then a click and it stays on. I even replaced the low pressure switch connector a while back.

 

[UmmScott]

thanks for the reply! Yes, I disconnected the HVAC controls and still get the AC relay request ON. I can’t remember when it comes on. I want to say the compressor has a delay, then a click and it stays on. I even replaced the low pressure switch connector a while back.

Ok...so thats a software thing..

If the relay were shorted, or the wiring was the problem it would be on immediately even when cranking the engine.
Since theres a delay, then that tells me that something is still giving an AC request.

The failsafe for most cars is to default airflow to the windshield and turn AC on.

Try disconnecting the high pressure safety or other pressure switch and see if you can do your crank relearn then

Sent from my SM-G975U using Tapatalk

 

[bigfootchiro]

Ok...so thats a software thing..

If the relay were shorted, or the wiring was the problem it would be on immediately even when cranking the engine.
Since theres a delay, then that tells me that something is still giving an AC request.

The failsafe for most cars is to default airflow to the windshield and turn AC on.

Try disconnecting the high pressure safety or other pressure switch and see if you can do your crank relearn then

Sent from my SM-G975U using Tapatalk

I disconnected all relays and the compressor at once, and it still commanded ON. If it were on immediately on startup, we’re looking at short or bad wiring? I would check it, but it’s not in my driveway right now.