My AC Battle


  • My AC Battle

    Thought I would write up what I have done to my AC to get it mostly functional.

    I have an 84 NA, when I got the car the defrost was stuck on. This became pretty inconvenient once it started warming up in Texas. I ordered a new aspirator fan from Courtesy and installed it. That fixed the vent issue, but the AC Gas light was on. A friend of mine has a set of AC gauges and is pretty good with that stuff, so he hooked it up and checked it. The car was registering 8lbs (of R12). I drove the car for a couple of more weeks and checked it again and it still had 8lbs in it. This gave us hope that there wasn't a major leak. The car had been pretty much just sitting with the PO for about 8 years, so I was hoping that was the cause. R12 is pretty expensive now and hard to find. I decided to switch the car over to R134a. We pulled a vacuum on the system for 30-40 minutes and checked the gauges for leaks. It was holding a vacuum, giving us the impression that there wasn't any. Since the system hadn't been open and exposed to the environment, we went ahead and put 2 cans of refrigerant in along with the necessary oil. The system was still not completely full, but was cooling. During this same time I was having problems with the vent doors not staying closed under load or just flat out not going where they were supposed to be. Sometimes, when I accelerated they would go to defrost with the heat on and not come back to the vents. Sometimes it would stay at the vents if the fan was on low, but hi would have enough force to push the door open a little and I wouldn't get air from the defrost or the vents. After reading here and the other sites I started looking at the lines coming off the tank. I replaced all the vacuum lines and that helped some, but still had the defrost issue under load. I started looking for pictures of the tank with labels, the diagram on the FSM wasn't quite clear enough for me. I found the picture I needed at http://www.88hybrid.com/vaclines/vaclines.htm, it's the one of the 85T vacuum tank. Hooked my lines up like that and that made everything almost perfect. Under normal acceleration the vents stay blowing, under heavy load, they will still get weak and/or blow warm air. It is very livable now. I have a thermometer in the vent and the air coming out is usually between 42 and 48 degrees.

    This is just an account of what I have done to mine and is no way a definitive guide. The refrigerant I used was synthetic R134a called Artic Freeze (I believe) from O'Reilly's, it was around $20 per can. I used 2 cans of it and topped the system off with about 1/4 to 1/3 of regular R134a. Normally, you are told to change the seals, the oil in the compressor and the dryer when you do this change. Like I said, since the system hadn't been open and seemed to be holding some charge, I skipped it. I suspect a new compressor my be in my future, the system doesn't cool as well as it should sitting at a light. When that time comes, I will most certainly do the full change. The dryer is only about $20 and the seals are around $12. The compressor is around $270 at O'reilly's.

    I haven't changed the vac lines under the dash yet, that could be another source of my problem or weak/leaky actuators. When I take the dashboard out to be replaced or redone, I will put new lines in on all the solenoids and actuators. Hopefully this will help someone.

    Edit, as is pretty readily found, NA cars have the cruise control line running off the intake. Turbo cars have an electric vacuum can under the vacuum tank that runs all the accessory vacuum, so the cruise line is connected to the very top port on the tank. I just capped mine off with a piece of hose with a screw in it.

  • #2
    I just did an R134a conversion on my car earlier this summer (along with a rebuilt compressor, because mine had developed significant bearing noise). Nissan has a well written TSB describing the process for converting most of their 80s and early 90s R12 systems to R134a. I found it here: http://maxima.theowensfamily.com/tsb/NTB96-023a.pdf

    There are 2 things that I can see might cause problems down the road:
    Your dryer probably does not have an R134a compatible desiccant. This may lead to the desiccant breaking up, and clogging your system. Second, your system lacks a high pressure cut-off mechanism. R134a can go over pressure much more easily than R12. Nissan recommends changing to a binary cut-off switch. Without this you are more likely to damage the system/compressor or cause the safety vent to trigger especially if the system is ever overfilled with refrigerant.

    Parts/supplies that I used:
    R134a gauge set
    Electric Vacuum Pump
    5.1oz PAG 46 (you could probably use POE oil, but Nissan recommends PAG)
    30oz R134a (2 1/2 small cans)
    R12 to R134a adapter fittings
    Dryer (I used a Four Seasons 33417)
    Binary Cut-out Switch, to replace Low Pressure switch (Four Seasons 35829 was the closes I could find to the TSB specs that was the proper size)
    Replacement O-rings
    Rebuilt compressor (not required, replaced due to significant bearing/clutch noise)

    Quick summary of the process I used:
    Have R12 removed from system
    Add 2.5oz of PAG 46 oil to new dryer
    Install new Dryer, using new binary cut-out switch, use new o-rings if not included
    Remove Compressor, drain existing mineral oil from compressor
    Add remaining 2.6oz of PAG oil to compressor
    Reinstall compressor, use new o-rings
    Turn compressor over by hand several times to distribute the PAG oil
    Install R12 to R134a conversion fittings on to hi and low pressure lines
    Vacuum system for at least 30 minutes (the longer the better)
    Allow system to set under vacuum for 30-60 minutes
    If vacuum has dropped, check for leaks, fix them, then repeat the vacuum process
    If vacuum held, Charge with 26 to 30 oz of R134a
    Check system performance / pressures versus information in NTB96-023a TSB and the FSM

  • #3
    Thanks for the input. I actually found that TSB and have it saved when I was researching. I suspected that I would be replacing the compressor down the line, since it doesn't cool well at idle, so this was just a quick and dirty conversion. I have lightly read over the TSB and passed over the cut-out switch. Thanks for pointing that out. When I do the full replacement I will certainly include that. Did you get a decent price on the compressor? The best I found was about $270.

  • #4
    The best I found was Autozone with one of their regular 20% off coupons, which made it around $240 shipped with tax for me. Minus sales tax and the $10 core charge it would be about $210. I decided that for $10 I'd rather keep my old compressor, in case availability dries up and I ever want to send it off to be rebuilt (or give it a go myself)

  • #5
    Just an update, I did end up putting a check valve in at the plenum leading to the vac tank. This solved my issue of going to hot air thru the defrost vents under medium to hard acceleration. Totally worth the $5 it cost me.

    Thanks for the info Leonard.

  • #6
    No way? What year z?

  • #7
    1984 GLL NA. The problem isn't 100% gone. I would say it is 95% fixed.