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.
i have a 2000 xterra se and the a/c works great in the morning and in the afternoon and when i hit a good bump in the road it goes off and blows hot air and hit another bump and it kicks back in what should i look at first evaporators thermostat??any help would be great before i start replacing things that dont need to be replaced
Hi Jack Smith,
I would say that the thermistor, (Nissan calls it a thermo amplifier), is faulty because of the voltage on the black/blue wire. I am concerned with the 13+ volts you found on it though.
Check to make sure there are no added or jumped wires in the system.
I just replaced the thermo control amp on my girlfriend’s 2000 Nissan XTerra and the AC started blowing cold air immediately. Finally, after the summer from hell and over $1000 blown on two different mechanics. What a PITA it was to reach my hand in to install the TCA but it was worth it. I took pictures if anyone is interested.
I have a 2000 xterrs and the ac was woring intermittently. Now it works rarely. I tested the voltage and got 13+ volts at both the green/orange wire and the blue/black wire. Is this a faulty thermister or is there a short somewhere in the system?
Assuming the you have tested the other two wires and everything is okay, then the thermistor is faulty. The thermistor is controlled by the inputs listed in the test information and switches due to evaporator temperature.
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.