This 2000 Nissan Xterra came in with the complaint that the a/c works good sometimes but it may not work at all at other times. The easiest place to test is at the thermistor lead connector (white) at the bottom left of the glove box.
It can be done without removing the glove box but it is easier with the glove box assembly out of the way. There are two screws located in the lower corners. Two screws located in the upper corners and two screws located in the upper center at the latch bracket.
The testing is as follows. Key on and engine running with the a/c turned on: Green/orange wire will have battery voltage from fuse #29 in the underhood fuse box, the Blue wire will have battery ground from the a/c control assembly and the Blue/black wire will have a nominal 4-5 volts with the thermistor off (temperature below 40 degrees F) and less than .5 volts with the thermistor on (temperature above 45 degrees F). The thermistor assembly applies a ground to the circuit which is sent through the dual pressure switch and then on to the engine control computer. This one failed the test and needed to be replaced. The proper way is to remove the refrigerant and then the evaporator case but I prefer a simpler way. It can be a little painful but it only takes about ten minutes from this point to change it. There are three phillips headed screws that have to be removed along with three 10 mm headed screws as shown in the following pictures.
Once the screws are removed, the two halves of the evaporator case can be separated enough to look in, see the thermistor, carefully and a little painfully insert your hand into the box and removed the sensor. Slide the new one in, in the reverse order and install the previously removed screws. The long tab pointing down slides into the evaporator fins and tab pointing to the right is the actual thermistor bulb.
Hi Sparky –
I have the Hayne’s manual for reference, and the Nissan wiring diagram as well. I have 4.5vDC coming on GRN/RED from the ECCS (“AIR CON”) to the Triple Pressure Switch, and continues through the switch on the BLU/BLK out to the TCA, still 4.5vDC on BLU/BLK at the TCA with the TCA connector unplugged. With the connector plugged it’s 0.0vDC. TCA has 12.6vDC on the GRN/ORG. All fuses check good visually and with VOM. AC clutch relay has pins 3 and 5 for sending power to the clutch, good 12.6vDC on pin 5, and if I jumper 5 to 3 the compressor comes on and runs fine, all pressures and temps check normal and the AC blows cold. The coil of the relay is pins 1 and 2, has 12.6vDC on pin 2 from the fuse, and 4.5 volts on pin 1 (pink) to the ECCS (“ACRLY”). BLU at the TCA is ground through the AC controls on the dash, they all work normally and check out OK for resistance with the VOM. Relay is new, and tried swapping it with the fan relay as well. TCA is recent. Is it the ECCS itself? Thanks!
Obviously check your fuses first. After that keep in mind that the 5 volt reference signal on the blue/black wire is sent from the engine control computer through the pressure switch and then to the TCA. I would go to the pressure switch and check for the signal from the computer and check system pressures.
Thanks for the great advice, Sparky! I also have a 2000 Xterra, Blue/Black showed 4.6v all the time, so I replaced the TCA (local Nissan dealer retail $52), the AC worked for a few weeks but then the AC relay stuck closed, engaging the clutch and draining the battery each night. New relay went in, but now the AC does not come on, new TCA shows 0.00v all the time. Jumpering the AC relay turns the compressor on and all AC pressures and temps are normal (I have a gauge set). What is the proper way to jumper bypass the TCA to test it? Connect Blue to Blue/Black with a jumper wire? 100 ohm resistor? Pressure switch bad?
If yours is the same model as the Xterra in the post, the ground signal leaves the amplifier and then goes to the pressure switch where it is sent to the ecm. What was the voltage on the blue/black wire with the system on?
I have an electrical issue with my A/C. The best I can tell there is no voltage going to the coil to close the A/C relay in the fuse panel. If I pull the relay I can jumper the 2 leads and the compressor comes on and the AC works. I have checked the thermal amp and it is ok. Someone is telling me it maybe something on the ECM. Any suggestions?