Friday, January 5, 2018

Fix your car's AC with 3 zip ties and save $900

Last summer, it seemed like the AC in my 2003 Nissan Sentra stopped working. I would turn up the fan, and I would hear the fan become louder, but air no additional air (of any temperature) came out. Atlanta in the Summer without AC is a markedly unpleasant experience. For a while I just rolled the windows down, but that has limited utility once July rolls around. 

I took my car in for repair. I had thought that maybe a hose had come loose and the CA (conditioned air, being the thing created by the air conditioning) was being dumped into the engine compartment, and hoped that would be a relatively inexpensive fix. The Nissan folks told me that the entire HVAC "computer unit" would need replaced, for a cost of $900. They then came back and said that they couldn't do the repair anyway since they couldn't order the part from Nissan, who had discontinued manufacturing that unit. They told me that if I managed to acquire such a unit, they could install it and just charge me for the install.

While I was looking at eBay and other sources to see how cheaply I could acquire the unit, I noticed that air was coming out of the defrost vents -- cold air, if I had the AC on. I realized that the core AC and fan components were working fine, but the knob that controls where the air comes out had stopped functioning and stuck on defrost regardless of where the knob was set. A bit of web searching discovered that this was not an uncommon problem, so I dived in. 

Alas, the lighting conditions for these photographs were suboptimal; I had to perform the procedure at night so I wouldn't be sweltering.

First, snap off the big plastic bit that covers the lower control panels:

Second, you need to remove two screws to remove the HVAC's bezel:

Third, you need to remove the plastic covering the middle vents:

I had to unplug the radio to be able to maneuver:

Now we can see the culprit. The rear of the vent selector knob is the big chunk of white plastic, with a metal rod that slides in and out of the black sheath with the shiny end. In the defrost setting, the big chunk of white plastic moves far enough to activate the microswitch on the lower right of the photo. There's supposed to be a clip that holds the shiny end of the black sheath in place. You can see it's broken off, with the result that turning the knob makes the metal rod push and pull the black sheath instead of sliding in and out of it, so the actual setting stays the same:

I used three zip ties and some epoxy/glue/sticky-something (I don't remember exactly what) to keep the shiny end in its place:


Unfortunately, at some point in this process I accidentally broke the clip that holds the corresponding black sheath for the temperature setting in place:

The clip was still in place, it just wasn't snapped on all the way, so I was able to use the temperature control as normal for about six months -- I just tried to avoid turning it unless I absolutely had to, and I turned it slowly when I did. It finally broke a couple days ago and is now stuck on the full heat setting. Luckily this isn't too terrible since it's freezing out and I generally want the heat on anyway, but when Spring comes around I'll need to dig back in there again and fix it.

There was another problem. When I plugged the radio back in and started to screw it back into place, I got disturbing sparks between the radio chassis and the car chassis. (Yes, I should have disconnected the car battery before beginning my expedition). I got out my multimeter and measured an 8 volt difference between the radio chassis and the car chassis. Needless to say, this was a BAD THING. The rest of the car appeared to be in working order, so I presumed the fault was in the radio. It had been working fine that day; I have no idea what went wrong. I took this opportunity to replace the radio (whose CD player had died years ago) with an aftermarket radio with an aux input jack and USB and SD card readers that I got from Fry's on clearance for around $8 -- but that is the topic for another blog post.

Here is the radio that bit the dust: