air conditioning re-charge, help!

[Roc87]

Does anybody have knowledge of A/C manifold gauges? I'm TIRED of having to rely on a buddy I've known since grade school to find time to fill my A/C. I bought a set of gauges and a vacuum pump off ebay, but I'd like to hear the proper way to use them. The GN was converted to R134 right after I first bought it about 7 years ago and has worked fine (Minus the front mount), but now the compressor is cycling, so it's low on R134. Plus the Elky is needing a charge, it was just filled last September, but it won't even cycle the compressor anymore, so it has a huge leak. Then the wifes car doesn't seem to be as cold as it used to be......So I think if I can figure out what to do, the gauges will be saving me a bunch of $ Not to mention I know of a few guys who'll buy lunch for filling theirs!

 

[notacarlo]

Well, when you hook the gauges up, keep the low pressure (blue in most cases) closed. and watch the high pressure side. If you open both, the HP will dangerously leak over to the LP side.
If I remember correctly, most systems are 38-50 psi low and 200-260 high. I have heard as much as 300-350 HP but I think that actually trips the HP swith and the compressor will cycle like you are low on 134.

When topping off the system keep the can or bottle upright and do a gas feed. If it is really low fill with the can or bottle upside down in short blasts.

BUT before you go this route, evacuate the system and check the orifice tube for metal shavings. Sometimes that is all the problem is. Do a tube swap, pull the system dry and refill.

Hope this helps.

 

[notacarlo]

Also, weigh the bottle before filling. The emissions sticker on the AC box will tell you (in most cases) how many lbs of refer need to be added to a dry system. This way you can monitor the exact ammount added. This will also show you an the gauges what the correct pressures are - pending that the rest of the system is in good shape.

 

[Roc87]

Appreciate the tips! I was unaware that the emissions sticker would tell the lbs. needed.

 

[notacarlo]

since I don't have AC, I cant remember if the TR does say that. My f350 does, murano does, saab does, 96 Sub does.

 

[jeffwiz87]

when a r-12 to r-134 conversion is done the proper fill of r-134 freon is 80% of the r-12 charge number on that sticker. whatever the car calls for originally you should only fill 80% of that.

 

[turbojimmy]

when a r-12 to r-134 conversion is done the proper fill of r-134 freon is 80% of the r-12 charge number on that sticker. whatever the car calls for originally you should only fill 80% of that.

The 80% is a rule of thumb, but not a substitute for charging to the right pressures using the manifold gauges. I bought "Automotive Heating and Air Conditioning (A Haynes "Tech Book") that helped a lot.

I went through the same decision making process a while ago when I wrote this article on Turbo Regal Web Site
AC 134a Retrofit

I've used the gauges and vacuum pump numerous times on my cars and other people's. Having them has saved me TONS of money over the years.

You should charge to about 25-30 PSI on the low side. The book says that for a 1987 RWD vehicle that the high side should be 130-190 PSI on an 80-degree day. I know mine is a lot higher than that (probably 220-230) but it works fine. In addition to watching the manifold gauges, monitor the air outlet temp from the center outlets on MAX A/C. Once the temp stops dropping it's fully charged. If it starts going up you're overcharged. I use an extra EGT gauge setup for this - works great and is very accurate.

The manifold gauges have a high gauge (red) and a low gauge (blue). There really should never be a reason to open the high-side knob up while it's connected to the A/C system (at least for most DIY jobs).

To charge the system, hook a can up to the yellow hose and open up the blue knob. You'll see the blue gauge react to the pressure from the can and the system should 'draw' the refrigerant in. The gauges register pressure whether the knobs are open or not. Whatever is hooked up to the yellow hose gets the pressure from the system when you open the knob on the manifold. This is why you NEVER open the red knob with a can attached to the yellow hose. It will expose the can to 200+ PSI which can grenade it.

Jim

 

[Roc87]

Well the gauges arrived, hooked them up to the elky ('88 GTA) and the low side showed 20psi, so I figured that was a good sign that it didn't have a huge leak. Shorted the low pressure switch to check operation of the compressor and it kicked on and sounded fine. Found a coupon to checker for buy 2 cans of R134a and get one free. After I got most of the first can into the system, and the pressure switch didn't need to be jumped, the compressor started to get angry. It sounds horrible. So now I've got to get a new compressor. But you were right, the elky has a sticker on it that calls for 3.5lbs of R12, my wifes caddy had a decal showing 2lbs. Once I get the new compressor put on and vaccuumed dry, I'll add the 80% of what the decal calls for.

Thanks for all the help and suggestions.

 

[Abomb]

Roc 87 I'm no a/c expert but I think your compressor is sounding angry because it needs the oil that you have to add with the R-12. Did you add the oil to the system?

 

[Roc87]

I didn't add any oil, wasn't absolutely sure I needed to. When it was first charged last year sometime, the oil was added and I didn't know whether to add any or not since the system wasn't entirely empty

I have an A/C compressor on order along with a new accumulator and oriface tube, so once I have all that installed, I'll vacuum the system dry, add the oil and then the refridgerant