'99 Pathfinder, Replaced AC System, Comp. Clutch Won't Engage

[DetroitAC]

I think you've left disconnected a sensor or switch during these repairs, or as you've suggested it's broken or the wiring is broken. There is also a chance that your ECM or BCM (control module) has determined that the AC system has failed and has disabled it, disconnect battery wait 10 minutes, reconnect. i have no idea if Nissan ever did things like this, other OEMs have.

If it's a switch or sensor issue, it's time to make a list of all the devices you see connected to refrigerant lines with wires coming out of them and start the troubleshooting. 1st step, are they all plugged in? Next, If the parts diagram calls it a temperature sensor or thermistor, does it have resistance? If the diagram calls it a pressure sensor, maybe replace it if you can't find anything else wrong.

I have no idea how this truck is configured, here is what I'd look for to start:
Ambient temperature sensor (might be in front of condenser, might be in engine air intake)
Evaporator thermistor (in HVAC case)
Low/High refrigerant pressure switches or sensors (mounted to refrigerant pipes)

[JohnHere]

The pressures look good. I'm presuming that the ambient temperature was about 85°F.

In addition to what has already been suggested, it seems to me that the PCM, ECM, or whatever you want to call it isn't receiving the correct signals from the various sensors to turn-on the compressor relay.

Even if the Check Engine light isn't illuminated, it's possible that a stored trouble code from the earlier A/C failure is causing the issue. If you have a scan tool that can "see" the A/C system, I would look at that, clearing any recorded codes. If you don't have a scan tool, an A/C shop or maybe even AutoZone, O'Reilly, etc., could scan it for you. The auto parts stores often will do this gratis.

If the scan turns up no codes, then do a visual inspection as mentioned earlier. If everything looks good, you'll need to get hold of an electrical diagram to trace all the sensors' inputs into the PCM that have to do with the A/C system's operation. It could turn out to be a bad pressure switch, ambient air temperature sensor, cabin air temperature sensor, frost switch, control head, or even a clogged cabin air filter if your vehicle has one.

[knotworking]

Well, I just got my weekend back, thanks Detroit!!!
Pulled the negative off the battery for around 30 minutes, hooked it back up and the clutch engaged properly
My AC controls only go down to 65 degrees, but it was blowing mid 40's straight out of the vents. You and John saved me from months of sweating in my seat!

My static pressure looks like it's a little high, but I don't have a reliable thermometer outside. I'm guessing it's probably 92-94 degrees out and the psi looks like it's 116 (pictured below). The other pic is the system running under full load for a few minutes. Anything look amiss? I'm temped to take it to a shop and have the system evacuated and refilled properly. My new my worry is putting undue strain on the system because I'll be running the AC full blast until December

[JohnHere]

We share your joy in getting the compressor running.

The slightly higher pressures are probably due to reduced airflow through the condenser while the car is setting there, likely at idle speed. Better would be around 1,800 RPM. Are you sure you caught it while the compressor was running and not momentarily cycled off?

You could take it in and have a shop recover, evacuate, and recharge it to specs. Or if you'd like to tinker, purchase a professional refrigerant scale from the site's sponsor and do it yourself. A good scale will probably cost a bit more than a shop's services, but you'll have the scale for future jobs when your relatives and friends find out about your new-found talents and ask you to service their vehicles' A/C

[tbirdtbird]

Great job!

[Cusser]

"Never trouble trouble until trouble troubles you"

"Don't mess with success"

By the way, the official manual for the 1999 Nissan Pathfinder can be downloaded; I did such for my 1998 and 2004 Frontiers.