| Hello fellow Z fans, sorry in advanced for a long post. :) My car is a 1993 NA. I have owned it since January 1998. In August of 2001 while on a 10 hour trip the AC stopped working. I was driving on the interstate and all of the sudden I noticed a kind of cold/white smoke coming out through the top vents. At the time I wasn't sure what was going on and then shortly after that the AC stopped blowing cold. After a bit of research I concluded that the evaporator sprung a leak and all of the freon came out. I did some reading up on the evaporator replacement and that looked like a big deal and kind of expensive so I thought that I would fix it some day in the future. Then in July of 2003 I was driving in town when all of the sudden the car died while I was at a stop light. I put on the hazard lights and popped the hood and noticed that the AC belt was split and laying on the ground. I picked up the AC belt, closed the hood, and restarted the car and drove home. After a bit of investigation I noted that the AC tensioner pully had locked up. The compressor turned and still turns fine. That was kind of strike two for the AC and since then I have just enjoyed the car with the tops off when its warm out. Flash forward to 2021 and I'm thinking I would like to try to repair the AC. If I can't fix it reasonably enough no big deal. I obviously have owned it for almost 20 years now without functioning air conditioning. But I kind of think it would be an interesting project to try to repair it. I have done a bunch of reading on the Z AC system and have used articles like this https://conceptzperformance.com/wiki/index.php/Air_Conditioning_System and https://alt.autos.nissan.z-car.narkive.com/ZNP0Ylhu/any-advice-on-replacing-a-c-evaporator-on-96-300zx and a bunch of other posts/articles Rather than buy a bunch of parts and maybe not be able to get the AC working I decided to start by doing some diagnostics first. I bought a set of AC manifold gauges and I hooked up the low side gauge. The first thing I noticed that I wasn't expecting was the low side gauge actually had a few PSI of pressure. I didn't initially understand how the gauges worked and I ended up venting out the tiny amount of refrigerant (yes I understand this is a bad thing but I didn't at the time understand how the gauges worked) that was still in the system. It couldn't have been much as it just read 2 PSI. Since it unexpectedly had some pressure in it thought as a next troubleshooting step I should see if it holds vacuum. I had assumed it wouldn't since I believe there is a leak in the evaporator. I know that if I did replace the evaporator I would need to also replace the dryer and then put it under vacuum for several hours and confirm that it holds vacuum. So via the manifold gauges I hooked it up to my model airplane vacuum pump and I was able to pull ~-20 PSI at the low side and negative something at the high side. Hopefully you all can see this picture. https://i.pinimg.com/originals/7e/3d/a7/7e3da74b1a602a914832efe211722dc2.jpg I took of the gauges. Then I closed the valve to the pump to see how well the system held pressure. Given my expectation that there is a leak in the evaporator I didn't think it would hold pressure very well. To my surprise it holds pressure really well. After 30 minutes it didn't drop the needle at all. This isn't something I expected. This made me think I should post the question to the experts here. I know that there is a bypass valve by the evaporator that bypasses the evaporator if the system gets too cold so the evaporator doesn't freeze. Is it possible that since I was on a long trip in August running the AC for several hours that the evaporator got cold, the bypass valve opened, and there was a leak in that circuit and that is why it still had a little bit of refrigerant in it and it still holds vacuum? Or am I misunderstanding how all of this works?
Thanks in advance everyone for your thoughts/advice/etc!
Ryan
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21:03:12 03/21/21
