2014 Maxima with suspected defective AC pressure switch

[SticktheCorners]

My AC suddenly stopped working after turning off the car for 15 minutes. Upon restart, nothing but hot air.
I have established that there is enough refrigerant in the system, but there are no clicking or other noises from the compressor or elsewhere and the AC compressor clutch is not moving.

The AC fuse is continuous but investigation at the pressure switch at the condenser gave some findings. The switch connector gives a voltage of 4.95v on one pair of the three terminals and 5v on another pair. In my mind, these are from the ECU.

I may have made a mistake testing on the sensor itself, since I checked for continuity only and not for a voltage. Since I have seen in another forum that this is a HALL type sensor, this may have been destroyed by this type of testing. In any event, since I was expecting to find continuity on one pair of terminals for a normal sensor, I found approximately .693 ohms on only one pair of leads.

Thinking my problem was this pressure switch, I already ordered a replacement which I will get shortly.

However, one big question is whether the pressure switch is on a valve that eliminates the loss of significant refrigerant from the system when it it is removed? This is hopefully the case since I’m hoping that the system refrigerant will not need to be vacuumed out by an AC technician somewhere.

Even though I have no check engine light, I have not pursued to check for any OBD2 codes.
Also, the local dealer has said that this is the only pressure switch in the AC system since I was expecting to find one on the low pressure side and another on the high.

Also, maybe this is a no no on this vehicle out of fear of blowing the ecu, but there are videos of generically shorting a pair of terminals on the pressure connector to complete the circuit to allow the electrical system to engage the clutch and compressor when the AC is maximally turned on. In my thinking, this would be a trial to see if the pressure switch could be taken out of loop.
Hopefully, avoiding doing this was the smart thing in this vehicle to preserve the expensive ecu.

[VStar650CL]

No, there's no valve. You should evacuate the system before replacing the sensor. It's a sensor, not a switch.
The vids you're referring to are for cars with triple switches, they don't apply to your Max. If you short your data wire to ground the ECM will think the system is empty and won't run the compressor, if you short it to 5V it will think the system is overpressure and won't run the compressor. Normal static voltage on those sensors is around 1V.

[SticktheCorners]

Thank you for your quick and helpful response. After thinking about all the hassles of putting vacuum on the system, loosing existing refrigerant and then replacement, it would seem the best course of action is to bite the bullet and ask the local AC techs to evacuate and replenish the system after the sensor change out.

I also went back to the sensor and tried to get a voltage on it after my shorting it out with the ohms testing earlier. I think there was .06 volts on a pair of terminals which might indicate a bad sensor, or resulting from my improper testing.
I will hope the new sensor does the trick.

Also, in view of what you said, I wonder if the correct polarity was know for the voltage from the sensor, whether a tired AAA or AA battery could be used to fool the ECU when connected to the proper terminals on the connector. If so, this would enable the ECU to compare the approximate 1v voltage and send a signal to the relay to switch on the compressor if everything else was without fault.

[VStar650CL]

You could certainly check it that way. Just jump plus to the data (Red) and minus to the ground (White) pins on the connector and see if the compressor will fire up. If it does, you know the sensor is screwed, if not then you know you're barking up the wrong tree.

[SticktheCorners]

The AC tech took one look at the compressor and noticed the telltale surface appearance of overheating and failure. It was so fast that he did not even charge me.

Considering my Maxima has 167k mileage, I’ll be reviewing my options. To be clear, a new Nissan compressor is quite pricey. The expected labor charge would probably put the repair at about $1500.

There is a big disparity in pricing compared with non-Nissan replacement compressors, so I have to wonder if there are off-brand replacements that have a decent reputation that is worth considering.

Secondly, how foolhardy is doing a DIY compressor exchange without a lift?

I would probably need to get a shop manual to help, but how much specialized disassembly is required that could be beyond a novice?

[SticktheCorners]

The AC tech took one look at the compressor and noticed the telltale surface appearance of overheating and failure. It was so fast that he did not even charge me.

Considering my Maxima has 167k mileage, but runs like a top with my recurring maintenance, I’ll be reviewing my options. To be clear, a new Nissan compressor is quite pricey. The expected labor charge would probably put the repair at about $1500.

There is a big disparity in pricing compared with non-Nissan replacement compressors, so I have to wonder if there are off-brand replacements that have a decent reputation that is worth considering.

Secondly, how foolhardy is doing a DIY compressor exchange without a lift?

I would probably need to get a shop manual to help, but how much specialized disassembly is required that could be beyond a novice?

[VStar650CL]

With 167K there's a pretty good chance the tech is right, but you can test the clutch yourself by putting the IPDM into Auto-Active Test mode. See PCS-11 here:
https://www.nicoclub.com/service-manual ... %2FPCS.pdf

If the clutch clicks audibly during AAT, it means your first instinct was correct and something besides the compressor is the matter. If it doesn't, then you know the clutch is shot or there's an electrical issue like a blown clutch fuse. Fuses rarely blow for no reason, so if it's the latter, chances are the clutch is shot anyway. The IPDM could also have a bad A/C Relay (requires replacing the IPDM).

If the clutch works in AAT, other possible causes of no-operation are:
* Dead refrigerant pressure sensor
* System has refrigerant but is overcharged
* Ambient sensor is open circuit (in the grille)
* Intake sensor is open circuit (on the evap, but there's an external connector on the side of the HVAC box)
* Cabin sensor is open circuit ( near the driver's right knee)
* Bad A/C controller (A/c Auto Amp)

You can get the skinny on your whole HVAC system here:
https://www.nicoclub.com/service-manual ... %2FHAC.pdf

If the compressor does need replacement, the simplest way to wiggle it out is to take the front two subframe bolts and the nose mount loose, to let the whole thing tilt forward. Doable without a lift, but not easy.

[VStar650CL]

PS - The sensors are all 2-wire and read "Siberia" when they fail open circuit. That's why the system will prevent compressor operation if any of them fail. The simplest way to test them is to short the wires together at the connector. That makes the sensor read "Sahara", so if the compressor suddenly kicks on, you know that sensor is dead.