I have a 68 with factory air. The air has not worked since I bought the car six years ago, but I have recently replaced the blower motor and the wiring harness along with some rotted vaccuum lines so I could get it running enough to troubleshoot. It had a small amount of pressure, but was definitely low on refrigerent. I added a 12oz can of R12 with leak detecter dye and ran the system regualrly for a few weeks, but saw no leaks. The pressure also remained constant, so if there is a leak, it is a very small one. This weekend, I added 36oz (3 cans) of R12 and now the system puts out "cool" air but not cold (about a 10 degree drop). everything seems to be working, but it is not nearly cold enough. Any thoughts on where I should go next? Expansion valve not opening enough? POA issues? More refrigerent? Evacuate and re-charge?

R12 is not cheap, so I don't want to waste any if I don't have to! Any help is GREATLY appreciated.

Dave
1968 RS/SS Convertible

Did you put a set of gauges on it? If so, what are the gauge readings?

I agree with reddoter, you really need a set of gauges to even begin diagnosing it. However, you can tell a few things just by observing the compressor (is it short-cycling or running constantly?) and by the temperature of the lines in different areas. Im thinking that 4 cans is a lil bit short on the refrigerant, but Im not 100% sure on that....

you need pressure guages on there to see where you at. high and low side. 1 can plus 3 cans equal 48 ounces which converts to 3 lbs. that may be too much for system and that is why it doesnt blow cold. r12 shouldnt be let out in air it should be recycled. it destroys the ozone layer. but before you do anything you need pressure guages on there. post back low and high side pressures. low should be 50-55 at idle.

For the time the system was idle, was it open to the atmosphere? Was there any charge in the beginning? If open or no charge, then the sytem should be evacuated.

Same time you put gauges onto the system, run the engine rpm up to 1500-1800 rpm and have a box fan in front of the car to aid cooling the condensor, set to max A/C, blower on medium or high.

Let sytem settle out for 10-12 minutes. As interior temp goes down, so will evap pressure. You're looking for a 30 PSI evaporator pressure equating to 32°F at the evap, hopefully.

As Bill suggests, you may have too much freon and it will never get cold. Also, if air has entered the system, the system won'r cool either with condensables in the gas.

If you charged with the standard “1 pound” R-12 refrigerant cans, they are actually 14 oz. which is pretty close to the 3.75 lbs. needed. Assuming, as Everett says, you evacuated the system first, you are fine with refrigerant. 30 lbs is your normal low side pressure. These systems, because of the POA valve, do not cycle. If you had air in the system and then filled it with R-12, at least one of your problems is air in the system, causing poor cooling.
Gary

You really need a set of gauges on it. Having pressure on the sytem prior to you adding refrigerant is a plus. You may have overcharged it. Did you check to make sure your heater valve is totally closed?
When you added the refrigerant you did purge the line of air before putting any in right?

This why Auto AC is not for the unknowing.
Too often most DIY'ers know enough to be damgerous.
You'll need to have it properly serviced.
ANY decent AC shop can recover your R12, and most can actually measure what comes out, evacuate the system and then reinstall the proper amount of R12 wether its 52 or 60 oz. They can then sell you the needed few ounces, or buy back the extra ounces.
Their buy back will be lower than the sell for price.
There will be a charge for this hours worth of time, the filtering etc of the R12 etc.

First, thanks for all the responses. I did use gauges, and I did purge the line before adding refrigerent. It is right at 30lbs on the low side. The system had minimal peressure in it when I started (around 3 lbs), so there should not be air in the system. The tube leading to the POA valve is sweating, but is not frosty. I checked the heater valve, and it was not closing completely, but now it is. When driving on an 82 degree day, the temp from the vent is about 65. I do not see bubbles in the site glass, but it is very hard to see for sure. It was suggested to me that this is how the system would react if the expansion valve was not fully opening.

A convert with A/C is going to be hard to cool in the sun, period.
Having 3 PSI int he system is from the ambient temperature heating up the system. If 3 PSI were there during the day, night time measurement will show much less.

Suction line to compressor should be sweating. Expansion valve could be stuck.

JMT.

You didn’t mention what the high side gauge was. The evaporator on its best day is capable of a 25 degree drop from the inlet to the outlet air. If you are running the car with the windows open, your temp drop is not that bad. It was said earlier, close up the car and run on max cold with the fan up for about 10 minutes and stick a duct thermometer in the center vent. That will be an accurate reading
The coldest tube will be the short one from the TXV to the evaporator. That tube should be very cold to the touch and should also be well insulated with tape. The line coming out of the evaporator and into the POA should never be frosted. If you look at a pressure/temperature chart for R-12, 30 lbs is 32 degrees, so if your POA is 30 lbs, it is working.
Gary

Like everyone else suggested, read your low and you did, but what is the hi side. If hi side does not rise to say 200 psi or so, even above 150, My guess would be , compressor is not pumping for what ever reason.
You said you purged lines, did you purge condenser? When you blew thru it, could you tell if it was equal to your hose pressure or volume? If not, condenser could be partially plugged and you can tell if the inlet side is a lot hotter than the dischard or outlet side. One other thing, I try to never purge a system with air, should used Nitrogen.
And one more thing, did you install a new drier?
If I were you, I would convert to 134. Obtaining R12 is almost impossiable unless you have a license or know some one under the table.....
Hope you added sufficent refrig oil.

instead of converting to R134A i would use R406A!!!

dont have to convert your oem equipment!
same oil used as R12 so no flushing required do to incompatiblity issues.

have used it in cars for years!!!

http://www.autofrost.com/

i would recommend replacing all rubber O rings with new style rubber compound.

but as always do your homework!!!!

Make sure the recirc doors are functioning.
You can test the expansion valve by removing the bulb from the suction line. Warming it with your hand will change your pressure readings.
Then dunking in a cup of crushed ice and water will change it again.
No changes, stuck valve.
Your 3 lbs of pressure was probably atmospheric pressure that was heated and pressurized the system. It should be evacuated and a new drier installed, The R12 can be recovered, filtered and returned to your system.