Got a 99 with auto climate, sat for 2years owner says it used to work but the fans don't do anything. I ran it through the self diagnosis HA fsm PG 70 and my in vehicle temp sensor isn't working but I don't think that's my problem here

 

You do want to fix that sensor because it will not regulate the temperature at whatever you set it at, it will only do full cold or full hot

The 2 most likely causes are the blower motor and the fan control amplifier (commonly mis-referred to as the blower motor resistor).

First check the fuses for the blower motor. There are 2 fuses, both 15 amps. They are in the fuse block by the steering wheel, left most column, the 2nd and 3rd fuses from the bottom. If the fuses are blown, the blower motor is no good.

The fan control amplifier is screwed into the heater duct behind the glove box. There are 3 wires on it. Turn the ignition switch to ON and ground the blue/white stripe wire (thick wire). Because it has 30 amps on it, there will be a spark when you do this. If the blower motor motor is good, the fan will run at high speed.

If the blower motor runs, the fan control amplifier is probably bad. There is a 3rd possibility, the the control panel in the dash. Nissan calls it the a/c auto amp, but this usually doesn't go bad.

 

is that problem common to 99 models? the 99 i was going to buy had barely any air coming out of it, i just figured blower motor, but at 155,000 miles i thought it was from sitting too long and it was something else.

 

Did you bother to check to see that it has enough refrigerant in the system? If it's out or low, the fans and compressor won't kick on.

 

If the volume of air is low, it could be the blower motor. The bushings for the armature may be binding and keeping it from spinning. It is also possible that debris (tree leaves and stuff) may have gotten into the blower motor squirrel cage. Take the motor out and put some jumper wires on it.

Another possibility that I have read about here on the org is that the diverter doors inside the ducts that direct the air flow to whichever vent openings you want may be messing up and ending up in a "half way" position.

 

I have to disagree with you. The blower motor circuitry is not inter-connected with the a/c compressor circuitry, so the fan will spin regardless of what is going on with the compressor.

The signal from the a/c auto amp (dash controls) that energizes the a/c compressor clutch goes through the triple pressure switch. The signal for the blower motor does not.

 

Now you have me doubting myself. I could have sworn that when you turn on the AC, not only does the compressor come on, but so do the fans.

Will check and report back.