Hi,
I'm trying to solve an AC issue with my 2011 S40 T5. When one looks at the live data when the car is running, it reports the "freon" pressure and it looks like I have a leak somewhere in the system. My question is where does the car detect this pressure? Is this being reported by the low-pressure sensor? I ask as I think I may have another ac issue as I did a R-134 recharge and when the pressure was 42, the ac system still didn't kick in, and I'm trying to determine where the problem is.

I know that the clutch will engage when it gets power and I already replaced the AC relay. The fuses are good. I want to disconnect the low pressure sensor and connect the terminals to see if I have a bad sensor. But if the sensor is reporting the actual pressure back to the ECM, this won't help as the ECM would cut off the signal to the clutch.

Thanks for your help!
Tom

 

Do you know if the A/C relay is engaging? If so, one of two things is happening.

1) The clutch in the A/C compressor is broken / open, and has to be replaced.
2) The air gap between the plates in the A/C compressor clutch is too large due to wear (a common thing on at least other models I've owned - assume it's the same on a 2011). This is often repairable with nothing more than something wedged in between the clutch mechanism and plate (slightly reducing the air gap to that which is small enough for the electomagnetic clutch to operate).

I can't tell how you're "reading" that pressure (VIDA, scanner, OBD smartphone app, :???). Might want to throw a "real gauge" on the system, if only one of those that are included with the "DIY fill kits".

 

To answer where - low pressure is detected by the switch on the return line (low pressure hose) - part #11 in the diagram. If the pressure is 42 psi - the low pressure switch will still be closed, it only opens if the pressure is too low - to prevent compressor damage. There is also a high pressure switch on the high pressure line to turn off the compressor if the pressure is too high (say the fans are not working).

From what info are you basing "it looks like I have a leak in the system"? Simple to find out - remove the refrigerant with a recycling machine. Modern machines measure the weight of what is taken out, you will get about 90%. Most machines will run a vacuum leak check during the evacuate and recharge process - the machine stops if it detects a leak or loss of vacuum. If it passes the leak test - Then put in the correct weight of refrigerant with the same machine. Takes less than an hour and at that point you know the system is full. Here's a part number for the low and high switches.

 

Thanks! Here's what I've done:

I've jumped the A/C relay and the clutch will engage. I've also measured the clutch gap and it is about .4mm, so within range. Using an Autel scanner, the Volvo's ECM module reports A/C pressure of 18 (I need to find that leak, but even after I've done the low-cost recharge with R-134a, the clutch hasn't turned on). Disconnecting the low pressure A/C sensor and connecting the leads on the electrical connector, I cannot get the clutch to engage. This suggests to me that there is no power going to the A/C relay R11 and I'm trying to determine why. Looking at the electrical diagram, it appears that the ECM module and the high pressure sensor are the two remaining possibilities for the problem. Note: The fuses F34 and F35 are fine. However, I don't understand how the ECM detects the actual pressure in the A/C system (which I'm guessing is keeping it from turning on relay R11). Looking at the electrical diagram, I see an actuator labelled 7/8 with three wires that connects to the ECM. I assume that is the high-pressure sensor. I haven't checked that yet as I haven't seen anyone reporting that sensor failing, but I will be tomorrow.

Finally, the green A/C light on the climate control panel turns on fine and I then get 12V at the low pressure sensor. Is there another place where I should be checking?

The car runs perfectly otherwise, so the ECM doesn't seem damaged otherwise. There's no obvious problem with the wiring either.

Thanks again for your help.

-Tom

 

Thank you! I will be following your suggestion to find the leak, but I wanted to first check that the mechanical parts of the system (and the electrical part) was working.

 

You do realize it's possible you simply have a bad climate control module? A good first step would be a scan with a compatible scan tool, preferably VIDA - and yes i realize you have "scanned" with your tool.

 

No, I didn't realize that this would be a possibility. Thanks for suggesting it. Is there a way to check that the Climate Control Module is bad other than VIDA at the dealer? I know my Autel tool isn't the same, but it's been very good about diagnostics for the car for the past five years. It hasn't been showing any CCM faults.

 

Do you have a wiring diagram? The compressor is 8/3, relay 2/22 powered by fuse 27. Note it's the ECM that grounds the relay to turn on the compressor clutch. 7/8 and 8/119 are the pressure sensors.

 

Thanks for the wiring diagram. In the end, I believe the issue may be a faulty low pressure switch. Here's what I was able to do:

1. I determined that the ECM is detecting the A/C pressure through the high-pressure a/c sensor. It has 3 wires, and the voltage on one of them sends info to the ECM about the a/c pressure on the high side. When I put more refrigerant in the system and got the ECM a/c pressure reading to be 50 psi, the clutch did turn on when the low pressure switch was jumped and it wouldn't turn on otherwise.

2. The 50 psi is being measured on the high pressure side when the a/c is not engaged. I have another working S40 from 2004.5 with a working A/C system and it shows 61 psi through the ECM when the car is turned on, but a/c not engaged. The pressure goes upto 175 psi when the a/c is engaged.

3. Knowing that the mechanicals are fine, I will take the car to a mechanic to have them find the a/c leak.

4. Weirdly, the high pressure sensor in my 2011 S40 T5 is not in the place indicated by the line diagrams (near the firewall on the passenger side), and where it is on the 2004.5. In the 2011, it is almost directly below the high pressure a/c fill valve and next to the throttle hose. It is very inaccessible. The a/c line is original, so it appears Volvo changed the location of the sensor for the T5.

Thank you for your help and your suggestions!

 

I know it's been a few years, but I'm seeing the same symptoms. AC works fine when I jumper the clutch, but the ECM isn't trying to turn on the compressor clutch. I haven't yet looked at the pressure switch and sensor. From the diagram above

8/119 - Switch (Low pressure?)

7/8 - Pressure sensor. 3 pins, not sure of the signals.

 

Just to answer my own question. The problem was the low pressure switch 8/119 failed open. Jumping the connector got the AC to work.

 

AC works fine when I jumper the clutch, but the ECM isn't trying to turn on the compressor clutch. I haven't yet looked at the pressure switch and sensor. From the diagram above