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This is my friends excursion that I’m just trying to fix the AC on but of course has turned into more work then it should. My problem is that the compressor will not turn on via the controls from dash and even jumping the low pressure switch. I had AC on and jumped low pressure switch and compressor did not turn on even though it should. So I reached all the way down with a power probe and got the clutch to turn on just to make sure it works. I need to know what tells the clutch to turn on and where I should go next. Could this be a problem with ac controls at dash or just a broken wire. And if it’s a broken wire would a continuity test be easiest method to figure that out.
Thanks for the help.
Go read this thread in its entirety. Although the OP never reported the outcome, that thread gives you critical information that I don't feel like typing all over again. https://www.ford-trucks.com/forums/1...eggspurts.html
Go read this thread in its entirety. Although the OP never reported the outcome, that thread gives you critical information that I don't feel like typing all over again. https://www.ford-trucks.com/forums/1...eggspurts.html
Report specific results if you have further questions or need guidance.
I read both of those fully and they had great info and I added them to my diagnosing notes page but do have some questions. My scan tool is just a basic love data one that shows no info about ac circuit so would it be worth it to get forscan and the adapter to see if the computer sees that the ac is being commanded on. I would think if the pcm does see the AC is being commanded on then it would be something further down the line.
I also am going to jump the ac relay since that powers the ac clutch directly and from my understanding doing that should turn on the clutch and ensure there are no wiring faults between the relay and the clutch plug.
so would it be worth it to get forscan and the adapter to see if the computer sees that the ac is being commanded on.
Absolutely. Handier than a shirt pocket...
I also am going to jump the ac relay since that powers the ac clutch directly and from my understanding doing that should turn on the clutch and ensure there are no wiring faults between the relay and the clutch plug.
Also appropriate and correct. Figuring out what does work shortens the list of what doesn't.
Another quick check is to jump the high pressure switch as they can also fail. Also, you can check the voltage on that circuit to see if there's an unexpected open that is inhibiting the ac request signal from getting to the PCM.
Also appropriate and correct. Figuring out what does work shortens the list of what doesn't.
Another quick check is to jump the high pressure switch as they can also fail. Also, you can check the voltage on that circuit to see if there's an unexpected open that is inhibiting the ac request signal from getting to the PCM.
What does the high pressure switch do in the system, my understanding is it turns the compressor off when pressure is high enough. Also should I jump both the low and high switches just to eliminate potential failure of one or the other.
And where would I check the voltage at to see if there is a open circuit.
What does the high pressure switch do in the system, my understanding is it turns the compressor off when pressure is high enough.
Yes, that's correct. Its a safety feature to protect the system in the event of certain failures. There's a further redundant higher pressure mechanical blow-off valve that fires when pressures hit dangerous levels if the primary cut-off happens to fail.
You can jump both switches, either singly (recommended) or both at the same time. You can measure for voltage right on/at your jumpers.
Yes, that's correct. Its a safety feature to protect the system in the event of certain failures. There's a further redundant higher pressure mechanical blow-off valve that fires when pressures hit dangerous levels if the primary cut-off happens to fail.
You can jump both switches, either singly (recommended) or both at the same time. You can measure for voltage right on/at your jumpers.
Ok sounds good, not sure when I’ll work on it next but I’ll be sure to update the thread if I find the solution for future reference for other people.
So we just got done diagnosing but to no success. I measured voltage of both pressure switch connectors and with ac on I had 12v on both connectors. With ac off there was no voltage so that leads me to believe pcm sees ac is being commanded on so it’s not the ac controls being a problem.
I also jumped pin 87 of the ac relay with a power probe and it activated the clutch so the circuit between the relay and clutch connector is good. I have power on pin 30 and 86, and measured with a power probe I have ground on pin 87. I never got any reading off pin 85 but in order for the relay to activate it needs to be given a ground. Does the pcm activate the relay by giving pin 85 a ground or is there something else wrong.
I also used forscan but nothing changed when I was look at live data and could only pull up a pod for the low and high pressure switch. And they never changed even when I had them jumped.
I’m at a loss right now and not sure where to go next. @projectSHO89
With ac off there was no voltage so that leads me to believe pcm sees ac is being commanded on so it’s not the ac controls being a problem.
If PID ACCS is OFF when the controls were set to A/C and both pressure switches were closed, then the PCM isn't seeing a valid input signal (12V) from the pressure switches. It then is an AC control problem. This assumes you didn't take that photo with the controls set to OFF...
If controls were set properly, you should have that 12V signal from the HP switch present at PCM C175 pin 41, a TN/LG wire. Suggest verifying continuity. I have run across at least on occasion where the wire was open in the insulation near that switch.
If PID ACCS is OFF when the controls were set to A/C and both pressure switches were closed, then the PCM isn't seeing a valid input signal (12V) from the pressure switches. It then is an AC control problem. This assumes you didn't take that photo with the controls set to OFF...
If controls were set properly, you should have that 12V signal from the HP switch present at PCM C175 pin 41, a TN/LG wire. Suggest verifying continuity. I have run across at least on occasion where the wire was open in the insulation near that switch.
Yes that photo was taken with the ac on and both connectors to switches jumped. Where is C175 at in the engine bay and do I test continuity from the wire that has no power on the HP switch connector to pin 41? I will also check to see if I’m getting 12v at pin 41.
If PID ACCS is OFF when the controls were set to A/C and both pressure switches were closed, then the PCM isn't seeing a valid input signal (12V) from the pressure switches. It then is an AC control problem. This assumes you didn't take that photo with the controls set to OFF...
If controls were set properly, you should have that 12V signal from the HP switch present at PCM C175 pin 41, a TN/LG wire. Suggest verifying continuity. I have run across at least on occasion where the wire was open in the insulation near that switch.
I probed the wire right before the pcm and jumped the high pressure switch with ac on and it did not have any voltage at the pcm. I then ran a continuity test on it and it failed. I am going to run a new wire from the TN/LG wire at HP switch connector to the TN/LG wire at pcm connector.
This fixed the issue, ran a new wire from the connector to the pcm. Was able to get it mostly filled up but then my can tap stopped working and I realized I need to get a self sealing can tap. So got that off Amazon and will fill it up fully at some point. But it got down to 54 while driving on a 90 degree day so decent.
