syc0path

As I mentioned in this thread I bought an R134a conversion kit for my '88 Trans Am, and I've been slowly installing it over the winter.

All the lines are connected, so I hooked up a vacuum pump to test the system. I ran the pump for about 10 minutes, and it pulled about 27in-Hg. Then I shut the pump off. Within 3-4 minutes, the vacuum had dropped to about 10in-Hg, so I thought the system must have a leak. But then it stayed at 10. In fact, I left it sitting for about a day and a 1/2 and it never moved off 10.

So is there a leak? It was also pretty cold when I did this (35-40°F) so maybe that could have an effect as well.

I tried searching online, but I couldn't find an example of vacuum dropping off this much without going to 0.

WildCard600

Did you try pulling down a vacuum again ?

DynoDave43

iTrader: (11)

So you left the pump attached? Not an expert here, but wouldn't that allow the pump to be a possible leak?

Seems weird that it held at 10.

syc0path

Not until u suggested it! I ran the pump again last night, but this time it stayed at 27. In fact, I checked it again this morning (about 12hrs later) and it's still at 27.

So what happened there? I'm picturing a scenario where an O-ring wasn't quite fully seated until it got sucked into place by the vacuum. That could explain why it stopped at 10 previously, and why it's holding at 27 now. But if that's the case, is it a permanent fix? It kinda reminds me of having a slow leak on a tire -- sometimes u can get it to stop by raising the tire pressure.

Yes, I did leave the pump attached. The way the valves are set up on my gauge set, I don't think there's a way to shut off the line to the pump w/o shutting off the gauges from the pressure in the system. But it's a fairly new pump, so it probably doesn't leak.

sofakingdom

iTrader: (1)

When you pull a vacuum on a system, any volatiles (water, solvents, the R-134 oil, etc.) begin to evaporate. This brings the pressure back up as miscellaneous gas molecules begin bumping around in there.

10 minutes is NOWHERE NEAR long enough to achieve a good evacuation for this reason. IMO ½ hr is the ABSOLUTE BARE MINIMUM.

The equilibrium vapor pressure of typical PAG oil seems to be around 28 in (I have no data to prove this... just anecdotal observation over the years). If you have a good vac pump you can get the vac below this, but after a time, it will come back up to about this value. That is normal and doesn't indicate a leak. The oil for R-12 has a lower EVP and isn't visible on a typical AC service gauge.

I would tend to discount the O-ring idea.

BizJetTech

iTrader: (3)

syc0path

Yeah that makes a lot of sense and explains all the observations I've made.

syc0path

I ran the pump again and it held vacuum, and I am now satisfied that the system is not leaking. So my next question is, how do I add PAG oil to the system? The old R12 systems used to have a pressurized can of oil that went in the same way as refrigerant, but the new oil cans don't seem to have a way to attach to the gauge manifold. The sticker on the compressor says the oil capacity is 135cc.

And then the next question is how much refrigerant do I put in? I suppose that's a question for the manufacturer, but I contacted them yesterday and still haven't heard back. Seems like that info should be included w/ the installation directions...

Bob88GTA

iTrader: (2)

I always added the PAG to the Compressor and Dryer BEFORE installing those components in the system...

DynoDave43

iTrader: (11)

syc0path

Well it sure would have been nice if the instructions had mentioned that! And thanks to DynoDave43 for the links to pressurized cans of oil... looks like that will save me the hassle of taking the compressor out again.

Next question -- how do I know how much refrigerant to put in? Again, this is the kind of information that should be in the directions I've heard that if u put in too much or too little, the system won't work properly.

I've already contacted the manufacturer twice and I'm still waiting to hear back...

Bob88GTA

iTrader: (2)

Put in 80% of the R-12 recommended amount...if it calls for 2.2 lbs of R-12, put in 1.76lbs and then go by pressures, temps, and such. Add as needed. Better to be under than over.
This is what I follow and have good results........35-40 degree air on a 90 degree day. Your results may vary. Will NEVER be as efficient as R-12

sofakingdom

iTrader: (1)

I prefer to be slightly OVERcharged...

I've had quite a few AC systems over the years, but I don't think ANY of them acquired more Freon from the atmosphere as time passed. They only way it changed, was to lose it.

Meaning, if you start out under, it just gets steadily worse; but if you start out slightly over (emphasis on "slightly") then as the system ages and the inevitable few molecules find their way out, you pass through "optimum" for a time.

syc0path

I finally got thru the manufacturer's tech support number (after being transferred a few times). He mentioned the guideline of adding 70-80% of the R12 amount. In this case, he said to add about 25-28 oz of R134a.

I also asked about the oil, and he said that the compressor is already charged with oil and that I shouldn't add any. He said there should be an orange sheet that was included w/ the kit that explains this. I'll have to dig back thru the boxes to be sure, but I don't think I got the orange sheet.

syc0path

I'm trying to charge the system w/ a gauge manifold, but the problem is that the gauge set's valve doesn't turn in far enough to open the Schrader valve in the low-pressure port on the accumulator. I've used this gauge manifold on other cars and never had this problem.

Are there different fittings/adapters that I'm not aware of, or is the port that came w/ the AC kit not manufactured correctly?

syc0path

I finally got ahold of tech support yesterday, and after some back and forth, the tech finally figured it out.

The accumulator has standard R12 ports on it, and the kit comes w/ an adapter to convert the R12 port to an R134a port. The problem is that the R12 port already had a Schrader valve in it (the directions really should tell u to remove it, but they don't). The port adapter also has a Schrader valve.

So when I put the gauge set on the port adapter, it pushed the valve in the adapter into the valve inside the accumulator. The valve plungers didn't perfectly line up, so the valve inside the accumulator was never opened.

So the fix is simple -- remove the adapter, remove the valve inside the accumulator, and reinstall the adapter. Unfortunately, the misalignment of the valves twisted the **** out of the valve inside the adapter, so it has to replaced. And a standard tire-style Schader valve tool isn't long enough to reach inside the adapter. So I have to buy an AC-style valve tool to fix it.