I'm running the dealer installed AC on my 73 with a 81-83 compressor and Freeze 12 refrigerant. I recently picked up a Harbor Freight AC manifold gauge set http://www.harborfreight.com/cpi/cta...emnumber=92649 and need to know the specs for pressure on both sides when the system is filled properly. I've searched using just about every combination of words I can think of, but so far nothing. Can anyone help me out?

Also, assuming I need to add some more refrigerant, what is the proper procedure to do that? The manifold has a fitting to allow this, but is there a specific sequence? And just to confirm, is it added to the low pressure side?

Any other words of advice and/or cautions from those who know AC systems? I know the theory of how they operate, but am without much practical knowledge.

Yes, it is added to the low side with the can or container inverted so as to charge with liquid rather than vapor. I look for a low side reading between 32-38 @ 1800-2000 rpm with the AC fully on and the fan on the highest setting. Start with both sides of the manifold closed. Keep the high side of the manifold closed and slowly feather the low side open and closed until you reach the desired low side reading. The high side reading will vary depending on the particular refrigerant used and the ambient temperature. You'll know when it's right when the center vent temp reaches the low 30s/high 20s. I use an infrared non contact thermometer for that but if you don't have one, a meat thremometer placed in the vent will do. Johnsen's Freeze12 is an excellent choice as I've been using it for over three years in my Z and my 810 with no problems. It contains no hydrocarbons and runs at a lower high side pressure than R12 or R134a, which puts less stress on the systems's seals, etc., and is a direct drop-in for R12. What type of fittings do you have on your compressor. Your link didn't work but I put the number in at the site and did see the gauge set. It's a lower end set but it does have standard fittings plus R134a type adapters. I have the R134a fittings on my compressors because I like the quick release which prevents loss of refrigerand when removing the hoses.

Thanks Stephen, that's just the advice I was looking for.

I do have another question. After swapping in the "new" compressor from the JY I added the lube from the ebay Freeze 12 kit, and then added about 2 1/2 cans of the refrigerant. I used the old skool method of adding until I didn't see any more bubbles in the drier (I didn't have the manifold gauges at that time). My goal was to just get the system up and running and verify no leaks. Also, I didn't know to invert the can which I now understand is important to keep get a proper mix of the Freeze 12 components loaded into the system.

Now I'm wondering if it's worth starting over by pulling a vacuum, and then adding with the can inverted. I would need to pick up a vacuum pump cheap. Is this HF unit worthy? http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96677 I'm sure it's not great, but is it good enough?

And is it worth doing this over? The cooling is marginal on a good day, so I figure any improvement probably does make it worth while.

I would check the pressures first. That vacuum pump should work but but I don't know how good one for 12 bucks would hold up. I paid $150 for 1.2 CFM Robinair 15100 pump 20 years ago and it still works fine.

I wouldn't say I'm new to Datsuns, but I have a 260Z with an airconditioning unit attached in the passenger footwell. Does anyone know if this was the original location, or an aftermarket unit?

I wouldn't say I'm new to Datsuns, but I have a 260Z with an airconditioning unit attached in the passenger footwell. Does anyone know if this was the original location, or an aftermarket unit?

If the evaporator is mounted in the passenger footwell it's aftermarket. Though there were aftermarket systems for the late 260 and the 280Z that did have a center mounted evaporator like the factory systems.

Really? Any idea where I could find aftermarket setup like that for mine?

I don't know much about AC systems beyond parts required and a general idea of how they work. The car has the Condensor and the Radiator in the stock places, and it appears to be stock parts. The compressor was mounted on the passenger side of the engine (removed by previous owner). The evaporator is a large unit, and it takes up most of the footroom underneath the dash, and looks just kind of tacky. It probably would work fantastic by the size of it though.

The old ARA dealer installed AC system that I refer to hasn't been made in years. There are other systems, like the Vintage Air system but they require a bit of work to install. The system you have, which was commonly installed on the eariler S30 has the main drawback of having to pull the cooled air through the system rather that pushing it like the center mounted evaporator. You can do the 'Honda blower motor upgrade' found on this site and that will improve the performance but it will never cool as well as the factory system or the aftermarket system with the center evap.

Really? Any idea where I could find aftermarket setup like that for mine?

I don't know much about AC systems beyond parts required and a general idea of how they work. The car has the Condensor and the Radiator in the stock places, and it appears to be stock parts. The compressor was mounted on the passenger side of the engine (removed by previous owner). The evaporator is a large unit, and it takes up most of the footroom underneath the dash, and looks just kind of tacky. It probably would work fantastic by the size of it though.

Sorry! I'm an idiot when it is 3AM :tapemouth

The condensor looks factory mounted infront of the radiator, and the drier appears factory as well. (I'm still tired, couldn't find the "Edit" button)

Do you know another manufacturer of the aftermarket center evaporator setup? I'd sell a kidney for the system. Really.

Not really sure if the aftermarket system used in the late 260 through 280Z would fit in your car. Is your's an early or late? Does the dash look like a 240Z dash or a 280Z dash. I don't know 260Zs very well but I think the later one with the larger bumpers also has the larger dash. If the early, smaller bumper 260Z has the 240Z type dash, the ARA type center mount evap won't fit. What type of fittings are used where the hoses connect to the condenser and to the rec/drier? Are they flare fittings or barbed fittings with hose clamps?

I'm lurking here and got a questoin to you Stephen, do you know how much freon sutch a system take.

Chris

Generally, depending on the system and type of refrigerant used, anywhere between 0.8-1.0 kg. or 1.8-2.2 lbs. I charge them by pressure and temperature rather than volume. I look for a low side pressure of 34-38 psi @ 1800-2000 rpm with the system fully on and blower fan on high.