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.
hey sparky thanks for your post. i tested my girlfriends 2000 xterra and its reading 4.5 volts all the time. it is 90 degrees outside where we are and we have the a/c set all the way cold. and when i put it at medium it stays at 4.5. is the thermistor activated by outside temp or by the setting on the dash? if its the dash how do u know the diff betw 40 and 45 degrees? thank you in advance…
The thermo amplifier replacement solved the problem in my 2001 Xterra. I had been having issues with the A/C not working only on the hottest days. On cooler mornings, it would usually work fine. I connected a voltmeter to the blue/black wire and could tell the thermistor was putting out less than 0.4 volts when the A/C was working, but was often up around 6 volts and higher when it would stop working. Thanks so much!
If your a/c box looks just like the one in the post, you do not have a cabin air filter.
I did the whole stick hand thing in there to clean out some junk and it seems to have helped. So looking at the first picture which looks just like my 2000 xterra plastic housing, does that mean there is no slot for a cabin air filter?
I am not at my shop, so I do not have access to wiring diagrams. I seem to remember that there is a circuit inside some of the asian blower resistors that affect the compressor operation. i also seem to recall at least one blower speed not working in those situations. If you do not resolve it by Monday, send me an email at the “Contact Sparky” link at the top center of the site.