2001 Nissan Altima SE, A/C Erratic

This 2001 Nissan Altima SE came in with the complaint that the a/c compressor would not engage properly. the customer stated that the compressor work fine sometimes. At other times it would click on and off several times before not coming on at all. Of course when I checked it seemed to work fien. Well I did have to charge the system properly first. after that it worked fine except for on flaw. The compressor would not cycle off and the evaporator core would start to ice up.

Since I already had a suspicion that the thermo amplifier was the problem (experience), I decided to start there with my testing.

The connector can be accessed without taking the glove box out. There are however only a few screws and it makes it much easier to work and take pictures. There are two lower screws. One at each corner. All have phillips heads.

There are two screws in the center at the glove box latch.

Then one in each corner. A little bit of pulling and maneuvering around and the assembly will come out. Removing the lower right kick panel makes it easier. Once it is free the glove box light will need to be twisted out of the assembly.

The evaporator case with the glove box assembly removed. The connector for the thermo amplifier is at the lower left corner of the evaporator case.

Since the compressor would not turn off testing was very easy. I first confirmed that turning the a/c switch in the dash off would cycle the compressor off, it did. I know the switch is good. Next, I had the engine running with the a/c on. Once the vent temperature dropped below 40 degrees “F” and the compressor was still on, I simply unplugged the thermo amplifier connection. The compressor cycled off as it should. I let the vent temperature rise to about 50 degrees “F” and plugged the connector back in. The compressor cycled back on. This test told me that all of the components from the thermo amplifier to the compressor were working as designed. The only conclusion was that the thermo amplifier was indeed the problem.

The connector from the thermo amplifier is attached to a bar on the evaporator case as shown below. A small screwdriver to release the locking tab and the connector will slide off.

The evaporator case is made of very flexible plastic, so you can separate the case by removing the two phillips headed screws at the case seam. Then remove the two lower screws that hold the case to the firewall edge of the assembly. They have 10 mm heads. With those screws removed you should be able to lift the two latches at the front of the case seam. this will allow the lower half of the case to be flexed down as shown in the picture below. Follow the wiring forward to the actual thermo amplifier. It has a bar that slides into the evaporator core fins.

With the case flexed down your hand should be able to go inside the case and grab the thermo amplifier body and slide it straight out to the left side of the car. Feel around to get an understanding of where the thermo amplifier is mounted.

Try to install the new part in the same place. If you are off slightly it will not make a big deal. If you try to place it to far away from the original location you may not get the proper vent temperatures. Also remember that the mounting bar has to be slid into the open spaces between the evaporator core fins. It should go in with minimal to slight force.

Perhaps the hardest part on this one was getting the case seam to go back together properly. I had to have one hand pushing the lower case up from underneath, while I used my other hand to flex the edges of both case halves around until it finally lined up and slid together.  You may or may not have the same issue as me but I thought it was important to tell you about it. If the case does not go fully together you will wind up with an air leak and a whistle.