Could not get the compressor to engage.

1. Check the compressor has engaged. Identify the location of your compressor. Look at the pullyer and you should be able to see if it spining or not. The engine running turn the A/C on max cool, set fans high, and make sure that the clutch is engaging on the compressor. The pulley spins any time the engine is running. The center part of the A/C pulley only engages when the A/C is on. If the clutch is engaging and disengaging rapidly, the refrigerant may be low. For more info check here: http://www.mercedesmedic.com/ac/

first thing is make sure the vehicle is in park, and emergency brake applied. next start your vehicle and let it get up to normal operating temperature. third turn hot/cold selector all the way to coldest. fourth turn the blower selector to MAX A/C double check its on MAX A/C and temp to coldest. the vehicle must be running for the a/c compressor to engage. when it does engage set on MAX it will cycle continuous which is needed to charge the system..
Okay so vehicles running, up to operating temp, A/c on max, cold knob to coldest.. your ready to charge the system! the kit you purchsed tells the

Not sure what vehicle you own, butcooling fan is a high current circuit that is operated by a low current circuit. It is not normal for the fan to operate constant. It usually indicates an electrical malfunction or an overheating condition possibly due to a stuck coolant thermostat. Depending on the vehicle. The fans may be designed to keep the engine temp from overheat condition.

The pressure on the low side it not very meaningful by itself.
What matters is the difference between the high and low.
The low normally can be up to 120 psi or so, and the high side can be twice that.
But when the AC is running, the low side should drop to less than when it is off.
But there could be lots of reasons for it not being very cold.
The pump clutch could be failing to engage. The release valve should be not opening. The air flaps could be letting heater air in instead of cold. The AC condenser fan fan or relay could be bad.
Etc.

I have the same car. The cooling fan activates at 227F. Only one fan will engage at this temp, the other one[closer to the A/C compressor] won't engage unless the A/C is working. Try charging the system with half a can of refrig. It'll be tough retrofitting to R-134A, the LOW PRESSURE connector is under the air box pointing sideways about an inch from a large bracket. Try and find a 90 degree adapter of some type and go from there.

Your AC compressor is activated via Climatronic control. The system regulates inside temperature activating the compressor or opening the flap from the heater core. This will be automatic when you set the temp you desired inside the vehicle. Unless you see the words ECON on the right side of the LCD display, your AC compressor will be engaged and the rad fan will operate to prevent the engine from over heating. Press ECON until you see it displayed and it will disengage the compressor and use only the interior blower fan to regulate the inside temp by opening the outside air flap and not from the AC.

The air gap may be too wide between the clutch disc and plate. It usually happens from wear. You can test this possibility by engaging the clutch electrically as you have done and then push on the disc slightly with the handle of a hammer or screwdriver. Be careful not to get your hand or fingers too close while the engine is running. Basically you are helping the magnetic field pull the disc in. I hope this helps.

Is that your static pressure readings??? If that is your static pressure readings that's good. When the engine running and fan on high and a/c compressor clutch engaged you should have 25 to 35psi on your low side and 200 to 350psi on your high side. If the clutch is engaged and that is your readings, replace your a/c compressor. Keep me posted, be glad to help.

Need clarification...
Does the compressor run steady, cycle on and off continually or even come on at all? If cycles on-off then attach charge manifold/gauge set and bring freon up to proper level. If does not come on at all, then start engine, turn a/c on, remove two-wire plug from low pressure cut-out switch mounted on accumulator. Jumper the wires at plug and see if compressor comes on. If so, bring freon up to proper level.

If charge level was low then check for system leak after system charge with an electronic leak detector if available.

If compressor runs but doesn't cool vehicle then with engine running and a/c on feel (carefully) the lines. High side line should be hot (be careful) and low side line should be cold. If these are both true then it's possible non-cooling condition is due to air temp diverter door not operating or heater valve not shutting off (if so equipped). If low side not cold it could be a plugged orifice tube. If high side not hot it could be bad rings on compressor. Both conditions can be diagnosed with a/c manifold gauge set by noting the pressures.

For safety... if not familiar with differences between hi and low side components or with charge equipment then please take vehicle to qualified person for service.

If all of the things you replaced are working fine I am going to say double check the thermostat. Also make sure your fan is engaging at temp. You cam check by running till warm and then running the AC. If the car does not overheat with the AC on then your fan is not running under normal conditions (with AC off) This can be caused by a couple of different things depending on how the fan is set up. I am not a nissan expert