A/C not working

With engine off.

Engine no same thing. Compressor not kicking on fan not coming on.

Hi again,

This could be a couple of things since the static pressure looks fine. I would suggest starting with removing the relay and let's check the entire control system from there.

Let's start with checking for 12 volts at pin 86 and ground, then 30 and ground with the key engine on and A/C on.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

If you have 12 volts on both, then both fuses are fine. Then jump one of those wires to terminal 87 of the relay and see if the compressor kicks on.

Lastly, we need to check the PCM to see if it is commanding it on. You do this by checking pin 85 for ground so put your meter on battery positive and then the black lead on pin 85. The with the engine and AC on the meter should read 12 volts. This shows that the PCM is commanding the relay closed and the compressor should be on. This means you have a relay issue, or the compressor clutch has failed.

https://www.2carpros.com/articles/how-to-check-wiring

However, if you don't have 12 volts then the PCM is not commanding it on. This could be a pressure switch or a PCM issue.

So, let's get to that once we know all this info. Please let us know what you find. Thanks

So, there are two relays to the A/C are we talking about testing the one on passenger side? When you say check the ECU readings with A/C on meaning car running?

There may be another relay that is tied to the A/C but not one that directly feeds the clutch.

Take a look at the wiring diagram that I attached last time and the one in the engine compartment directly feeds the clutch and gets turned on and off by the ECM so we need to start with this one.

Correct. The engine on and A/C on this way the clutch will come on. You can do it with the engine off, but you will have to listen for a single clunk from the clutch and that can be missed.

Just make sure you hook the meter to battery positive so you can check for ground from the ECM.

I also attached the info on the fuse box layout and relay so you can see the terminal layout of that as well.

Pictures say f47 and f49 are both A/C relays, but these are actually fuses. Both are good. I am having hard time finding which is the A/C relay. Also, i am using a power probe to check fuses, will it be okay to do so to check for 12v when i find the relay?

Yes. Sorry. Maybe I caused that confusion. Fuses 47 and 49 are the two fuses that feed the power circuits for the relay on pin 86 and 30.

So, if those fuses are good then we need to remove the relay on the same fuse block to jump the terminals of the relay.

See the attached for the relay information. It includes the terminal layout of the pins.

So, we need to jump 30 to 87 with the engine on and A/C on to see if the compressor starts running.

If it does then we need to check 85 for ground with the A/C on. Put your power probe clip on battery positive and then touch the probe to terminal 85 of the relay and your probe should show 12 volts.

If both of these check out, then the relay would have to be the issue.

Let me know what you find with this, and we can go from there depending on what you don't have as that will determine the direction.

Another thing i noticed is that the relays can all be installed one way or 180 degrees. so, how can i tell which is 87 as it can be in 2 different places?

Oh, i see. those numbers correspond to the clips in the fuse box not the relay.

Jumping 87 to 30 turns the compressor on. Touching positive probe to battery positive and touching the probe to 85 does nothing. Connecting positive and negative ends of the probe to battery the touching the probe to 85 i get 0 value but the negative indicator makes a sound. Even with multimeter touching red to battery positive and negative to 85 does nothing. Touching red cable to positive battery and the negative to 87 turns on A/C compressor. also touching a tester light to battery positive terminal and to 87 light comes on, nothing when i touch 85, so all tests are showing the same.

Okay. That is showing that the module is not grounding the relay to turn the compressor on, but the compressor and wiring are able to turn on.

So, we need to get into the control side.

Let's start with the pressure switches. I would go to the dual pressure switch and check for voltage on pin 4 to start.

If you have voltage on this wire, then the cycling pressure switch is fine.

Then check for voltage on pin 1. This is the signal that is going to the PCM to tell it that the low pressure is fine. Then check voltage on pin 3. This is telling the PCM that the pressure is not too high.

Looks like these are all on/off switches so you should have 12 volts on all 3 wires with the engine running and A/C on when you back probe the connector with it plugged in.

If you want to bypass this dual pressure switch then you need to remove the connector, jump pin 1 to pin 4 and then apply 12 volts to pin 3.

If the compressor comes on, then this switch is the issue.

And this is the switch on left front of the engine i assume. So even though the relay is kicking the compressor on, with the A/C on, the switch should still have these values?

One on the front left has 4 wires not 3.

That is correct. We are now onto the control side, so we need to check the inputs to the PCM to find out if something is telling it to not turn the compressor on.

Sorry. Yes. That is a 4 wire. One is ground so I just called a 3 wire because you have 3 "signal" wires, but it is a 4 wire.

Here are the connector views for each of the switches on this vehicle.

The second is the dual pressure switch that you are looking at.

By passed the switch by jumping 1 and 4, then applied 12v from battery and with the probe. Compressor did not come on. There is ground on pin 2. Nothing on pin 4, power on the other 2.

Okay. Let's do one more thing before we condemn the PCM. Jump 1 and 4 again, then 2 and 3.

Looks like the PCM is looking for ground on pin 3 so applying 12 volts may have not be exactly correct.

Jump 1 and 4 and at same tome jump 2 and 3 at the same time? And no battery voltage to supply?

Correct. Jump them at the same time then turn the key on.

If you look at the wiring diagram pin 3 is a voltage supply from the PCM to the sensor and when the sensor is closed, it supplies ground for that circuit.

So, if the PCM sees an open circuit on this circuit then it knows the pressure is out of spec and doesn't allow the compressor to run. So, if the circuit is closed the PCM will turn the compressor on so jumping it is just telling the PCM that it is good pressure.

Did that and turned it on the fan cane on but not the compressor. When 1 and 4 are jumped i probe 2 and it shows ground., 3 shows positive and battery voltage.

But then it is possible it's low on Freon so compressor not coming on.

Okay. That is correct voltage on 2 and 3.

Maybe we should take a step back because I thought we confirmed the pressure was correct but that was just static pressure.

Both sides (high and low) in that picture are 80 PSI?

If so, that seems fine. However, go back to the relay and just jump the relay and get the compressor to run again and check the pressures with the compressor running.

However, if the pressures are correct and jumping the dual pressure switch does not cause the compressor to come on, means the PCM is not commanding it on and appears to be the issue.

I attached a chart for correct pressures. However, with 80 PSI on both sides of a static system, shows it is full or at least full enough to get the compressor to come on.

Just seems like the PCM is not able to ground the relay.

Yes, that was static. does it always mean pressure is right just cause static is right?
I also have seen the yellow light blink sometimes or come on and off on the A/C display inside the car when i turn it on.

Yes, both about 80 PSI.and before the last readings i sent you for the pressure switch the relay was out lol. so, when i inserted it i got the right values. But i will try what you just mentioned.

So, connect the pressure switch or leave it i guess doesn't mean anything and jump the relay. Check the pressure and go from there, and see if the air is cold.

Exactly. You are bypassing the entire control side by jumping the relay, so it doesn't matter if the switch is connected or not.

Yes. Then check the pressures or at least make sure it blows cold. That will confirm that the pressures should be closing the dual pressure switch and the PCM should be grounding the relay.

Gotcha. No chance of the A/C head unit having anything to do with this?

And it's okay to jump relay temporarily like this right?

Yes. It is fine to install the jumper and run it to test it. The switch is nothing more than a metal contact inside the switch case, so by connecting a jumper wire, you are just acting like the switch itself.

Clearly it is not a good idea to leave it.

Also, the flash A/C light normally means there is a circuit issue or some other reason the PCM is preventing the compressor from coming on. This could be an electrical issue, sensor issue, or even a pressure issue.

I am attaching the info below from the manual that explains the system in more detail.

Basically, if you are bypassing everything and the A/C doesn't come on, the only way it is the A/C control module is if that is not sending the signal that you pressed the button.

The best way to check this is to monitor the A/C clutch request in the PCM.

Also, these OEM diagrams explain this a little better than the AllData ones. You can see the pin 2 and 3 of the dual pressure switch are for the cooling fan which is why that came on. However, the PCM still is not commanding the clutch on.

While it would be good to confirm this with monitoring the PCM, it appears the way this works is when you press the A/C button, it sends voltage to the smart junction block as you can see on the first diagram. The SJB then sends voltage on the A/C clutch cycling pressure switch. If the pressure switch is closed then it sends the voltage to the dual pressure switch on pin 1 and 4. The PCM is the ground for this circuit so if it gets 12 volts due to both switches being closed, then it commands the clutch relay to close.

We have already confirmed you have voltage at the PCM on this circuit, but the relay is not coming on. Jumping 1 and 4 of the dual pressure switch just eliminates the switch as being the issue.

Unless I am missing something, I think you need a PCM.

If you connect the entire system and start the engine and turn the A/C on, you should have 12 volts at pin 15 of the PCM C175B. If you do, then the PCM should be grounding the relay, but it is not.

I did jump 2 of the wires, compressor kicked in as well as fan and air is cold.

I don't want to fool around with another PCM right now. It is getting cold here in Alabama so i won't need the A/C for now. So how can i temporarily provide a ground for the relay until next year?

Maybe I didn't understand something. What two wires did you jump to cause the compressor to kick on? The two on the dual pressure switch? If you did then that switch is the issue.

As for rigging this up to take the PCM out of it, that is going to be tough because you can simply remove the relay and jump power directly to the compressor circuit, but the compressor will run all the time and you need to cycle the compressor, or you will over pressurize the system and blow a line off or freeze it up.

So, you could wire a switch and run it into the cap but you would need to cycle the compressor manually, but it needs to cycle based on pressures. This is why you have this pressure cycling switch on the PCM control circuit. Basically, that is a pressure switch and when the pressure reaches a certain point, it opens the circuit and the PCM cuts the compressor off.

So, this really isn't a good option but hopefully you jumped 1 and 4 of the dual switches and the compressor kicked on. If so, replace that switch and it should be fixed.

No i jumped the relay. The switch isn't even connected.

What i connect a ground the relay ground pin and since the dual switch works it should cut off the compressor if the pressure is too high or too low.

Take a look at the diagram below. If you put a ground on this circuit so that the compressor comes on, you are eliminating the PCM all together. Those sensors are on the other side of the PCM, so they are called inputs to the PCM, and this clutch relay is called an output.

The PCM takes these inputs and determines if the clutch relay should be grounded or not.

So, the PCM is what is turning the relay on and off and whatever you do, you are going to have to take the place of this. That means you need to have the input information (pressures in this case) and instead of the PCM deciding if the relay needs to be grounded or not, you would have to do that by adding and removing the ground so that the compressor doesn't continuously run.