A/C Issue - Possible Pressure Sensor

[BMiller123]

I've been struggling for a year now fixing my A/C system in my 2014 Nissan Altima, replaced the condenser, pressure sensor, compressor and expansion valve and still having issues unfortunately.

We put the car into the Self Diagnostic mode and the Compressor cultch will kick on during that test, but does not engage during normal operation.

I checked the connectivity between the Pressure Sensor and IPDM and the wiring is good.

The Pressure Sensor reads Green to White 5V, Green to Red 5V and Red to White 0 V.

The ambient temperature sensor is reading correctly, but I don't know how to check the intake air sensor. The Mass Air Flow sensor has 4 wires and I couldn't figure out which was which to test it.

A bit more background on my issue. My system stopped working at some point last year. The low side was reading 50+ PSI. I got a new control valve and expansion valve, put those in and the system worked for a week.

I thought I messed something up, so got another control valve and tried again, worked for 3 weeks and failed again.

So I dealt with it and just replaced the whole system, which we then realized it was probably something else since that did not fix it and it was still reading high pressures on the low side.

At this point I'm at a loss on what to try next to get the system working. Any advice would be welcome and appreciated.

[VStar650CL]

Couple things. First, I think there's a little confusion here. You say at one point that the compressor won't kick on, but at another point that the low side pressure is high. The pressures mean very little when the compressor isn't engaged, so which is it?

Second, I'm assuming you have an Auto system and not Manual, since there's no Intake Sensor on a Manual system. There are actually 3 different temp sensors which can disable the compressor on an Auto system. There's an In-Car sensor located behind a grille at the driver's right knee. None of them, In-Car, Intake, or Ambient can read "Alaska" or the compressor clutch won't activate. "Alaska" is 5V, all the sensors should read some "middle voltage" and not 5V or 0V (0V is "Sahara", so that probably isn't your issue). You can check the intake sensor at the pigtail connector on the passenger side of the HVAC box, it will be a 2-pin white connector with Pink and White wires. You probably need to pull the glove box to see it. White is grounded inside the A/C Auto Amp, Pink is signal. Backprobe Pink and if it reads 5V, either the sensor or the ground wire is open-circuit. Same procedure for the In-Car, drop the left lower dash and backprobe the sensor. White is again ground, Green is signal. The dash will tell you if the Ambient works. If the other two read normal middle voltages, the problem isn't a temperature sensor.

The pressure sensor is a different animal, and the wires don't end at the IPDM, they go through the IPDM to the ECM. The ECM is the shot caller. Normal static signal on the sensor (Violet wire) with the connector backprobed is about 1V at room temperature, about 1.5~2V with the compressor running. Orange is 5V supply, Sky Blue is ground. Most decent scanners can pull up the refrigerant pressure as streaming data. The ECM will cut compressor operation below about 20 psi (0.2V) or above about 400 psi (4.2V).

Lastly, the compressor on the Auto system is a swash plate type (the Manual uses a traditional cycling clutch). Swash compressors change the piston stroke to move more or less refrigerant volume according to demand. This is done using a solenoid (ECV) built into the compressor and run by the A/C Auto Amp (the Amp is located underneath the radio on a shared bracket). At the ECV connector, Blue should be constant 12V, Sky Blue should be 12V when the compressor is disengaged and a "middle voltage" when the compressor is running. Swash plates almost always stick at the bottom (minimum flow) when they fail, so there's an easy test for a bad one. If the system makes good cold with the blower on the slowest setting but the cold goes away when you crank up the blower, the culprit is a stuck swash preventing the compressor from moving enough refrigerant to meet demand. Note that an open circuit to the IPDM can also cause a dead swash, so make sure you don't have a bent pin at the connector.

[VStar650CL]

One other thought, when you say you "changed the whole system" did that include the plumbing? A broken dessicant bag inside the receiver drier will send pellets all through the system and clot the TXV for sure, and maybe the reed valves in the compressor as well. If that went undetected, depending the order things were replaced, you may still have pellets kicking around in the system.

[BMiller123]

Thank you so much for the detailed response! I've been going nuts trying to find any help on the subject and this is very detailed and helpful!

You are right that I am very confused on what I'm doing.

It is an automatic system. I do have access to a scanner that should be able to read those temperatures, it'll take me a few weeks to dig into this and troubleshooter as I'm limited to weekends working on this and seems like it may require a full day to test out a few things.

I did not replace the plumbing - the last thing we did was pull the TXV to check if it got blocked and it seemed to be fine.