67 Air Conditioning Problem

I have a 67 fastback that originally came with factory A/C.  The previous owner replaced the compressor (and possibly other components) with an Sanden unit.  The system is still running R12.    My problem is that the air coming out of the registers takes a long time to cool down and never seems to get cold enough especially on days when the temperature exceeds 80 degrees.  Also, the temperature gauge shows that the engine is approaching an overheating situation when the A/C system has been on for a few minutes, though it never actually overheats.  Visual inspection indicates that the compressor is working (i.e. the low side and high side fittings are cold and hot respectively).  Pressure readings for the A/C system prior to engaging the compressor are 80-85 lbs (both high and low sides) on a 75 degree day and 95 to 105 lbs on warmer days.  With the A/C system on high, and idling at 1500 RPM, the low and high sides read 25-30 lbs and 190-210 lbs respectively.  One other thing that I have noticed is that the condensation hose leading from the evaporator is very warm to the touch.  Condensation does come out of the hose when the system is  operational.  

Any thoughts or suggestions that would solve my problem would be much appreciated.  It is starting to warm up here in Texas and I need to resolve this problem.  

When was the last ime you added refrigerant? I thought Sanden conversions worked best with 134A. If your low  pressure side is under-pressurized like it seems yours is at 25-30 lbs., then the air stays warm. It should read about 40 PSI at 1500 rpm.
Add a little refrigerant. Buy a guage at Kragens, etc. and add R-12 until the guage reads at the middle to high range in the blue zone at 1500 rpm with the A/C on max high. Worse case is you may have to evacuate your entire system and recharge from scratch if you have leaks or did not added refrigerant for so long that the system is full of air. If that is the case then ditch the R-12 and convert to R-134A as long as you are starting over.
Just buy a guage and a can of refrigerant and add only when engine is at 1500 rpm and air is full on to the blue zone limit. Anything else will give you an erroneous reading. If that fails then bleed pressure out of the low pressure side (Blue cap) and refill/replace with fresh refrigerant. Don't remove all of the refrigerant when doing this or you will have to evacuate the entire system. Leave some in there and then add fresh to it. Hope that works. Remember to never open the high pressure line (red cap) yourself.  

The A/C condenser in front of your radiator will somewhat restrict and preheat the air going through your radiator and tends to run the coolant temp up a bit when at stop lights or at idle. Best fix is more airflow like an auxiliary electric fan to help with low speed air flow. In some cases it is a good idea to turn A/C off at stop lights to avoid temp rise. Once moving turn back on when there is more cooling air flow.
Some guys are going to kill me for saying this but I removed my 180 degree thermostat for summer driving in over 90 degree heat with A/C on to find that it helped slow temp rise and max temp levels. I replaced it with an old thermostat that Had the center rmeoved. Like donut looking a restrictor plate with more flow than a fully open regular thermostat. It aided coolant flow when I needed it most.
In the winter you need thermostat to help the car warm up faster and provide warm air to heater and defroster. In summer you won't be needing those things.  

You should also take a look at your radiator. I have one 67 with a 20inch 4 row and it will also heat up when the temp goes over a 100. On my other 67 I have stepped up to a 24 inch 3 row radiator with a 6 blade fan. since I have not got it on the road yet, I can't say how it will do.  

derryberry:
I have a 67 fastback that originally came with factory A/C.  The previous owner replaced the compressor (and possibly other components) with an Sanden unit.  The system is still running R12.    My problem is that the air coming out of the registers takes a long time to cool down and never seems to get cold enough especially on days when the temperature exceeds 80 degrees.  Also, the temperature gauge shows that the engine is approaching an overheating situation when the A/C system has been on for a few minutes, though it never actually overheats.  Visual inspection indicates that the compressor is working (i.e. the low side and high side fittings are cold and hot respectively).  Pressure readings for the A/C system prior to engaging the compressor are 80-85 lbs (both high and low sides) on a 75 degree day and 95 to 105 lbs on warmer days.  With the A/C system on high, and idling at 1500 RPM, the low and high sides read 25-30 lbs and 190-210 lbs respectively.  One other thing that I have noticed is that the condensation hose leading from the evaporator is very warm to the touch.  Condensation does come out of the hose when the system is  operational.  

Any thoughts or suggestions that would solve my problem would be much appreciated.  It is starting to warm up here in Texas and I need to resolve this problem.

The 25 psi on the low side seems a little low but may not be a problem. Put a therometer in the outlet of the evaporator and look at the discharge air temp. If its in the 40's or less your unit is working as good as it can. If it is not anywhere close, you have other issues; one may be bad airflow over the condenser,system line blockages, a bad expansion valve or thermostic switch, or even possible a bad compressor. If you still have a recvr/drier with a window, look for no foam or bulbbles when you accelerate the engine to 1500.  It won't hurt to put a little more freon in (if you can get it). but be carfull not to get that high side past 250 on a 80 degree day.

PS: You should not check the air outlet temperature with the air blowing on high cause you have the most throughput and least chance of heat transfer.  Remember, heat goes to cold in an AC system. set the fan to medium or slow.  

The previous owner indicated that he replaced the radiator.  How can I determine the number rows?  Also, the car runs a little cool until I turn on the A/C.  Within a few minutes at highway speeds, the gauge is reading warm to hot with A/C on.  Occasionally, the temp gauge will spike all the way up within about a second and then settle back down to the normal range.  

Occasionally, when I first turn on the compressor, I hear a rumbling almost like the fan is hitting the shroud, but I can't find any indication that this is happening, and the compressor is properly mounted.  No window on the receiver, but I do have a sight glass in one of the lines.  It shows bubbles with the system off, and very little if any bubbles with the system on.  Someone suggested spraying a mist on the condenser while watching the gauges.  This lowered the gauge readings significantly and also brought the register air temp way down temporarily.  I'm beginning to think I have a condenser airflow issue.  This might explain the engine near overheat situation when using the A/C.  

When the engine is cold carefully remove the radiator cap and see how many tubes in a row front to back you can see. That will tell you how many rows your radiator is. If the coolant is high and prevents you from seeing the rows then drain a little out until the rows can be seen and counted. Also check to see if any of your tubes are plugged with deposits. You might want to back flush or boil out your radiator if it doesn't flow well. It might only have enough capacity to take care of your engine without A/C because there is some plugging. Once A/c is added to the equation it becomes overloaded and can't get rid of the extra heat fast enough. The a/C condenser with A/C on actually preheats the air going through your radiator core and also acts as a flow restrictor by blocking air in front of the radiator. Everything needs to be in top shape for everything to work right.  
Early Mustangs are famous for A/C compressor rumble when the A?C is on and the engine is idling. It is usually caused by fan belt slap. The belt to the A/C compressor has to be VERY tight with almost no play. Ford even came out with a retrofit idler pulley that mounted on the engine under the compressor beween the compressor and the main crank pulley to reduce or remove the rumble and slap.
I put one on my '66 and it helped a great deal as long as the belt tension is very tight.
You might want to replace your thermostat. When your temp guage needle moves up and suddenly drops back again it is an indication of the thermostat opening point in most cases. A lazy thermostat isn't good...especially with A/C because by the time you get coolant flow its almost too late with the extra heat load put on the motor by the A/C. It will take forever to recover and get back to normal. You might try running a performance thermostat unit like a Mr. Gasket and think about a 160 degree opening point for summer use. That way the engine coolant starts flowing ahead of when it will be needed most when the A/C comes on. Once you go beyond system limits you will only build heat and the temp guage will continue to climb. You will be adding heat faster than your sytem can get rid of it. You can help curb that by starting flow sooner.
Try adding a little refigerant to your system.
Do you have an A/C fan and shroud to help pull air flow across the radiator core.
The fact that it heats up when you are going at cruising speeds might indicate the plugged radiator or bad thermostat. Airflow at cruise speed is good and any heating after that is usually cooling system or engine related more than anything else.  

derryberry:
Occasionally, when I first turn on the compressor, I hear a rumbling almost like the fan is hitting the shroud, but I can't find any indication that this is happening, and the compressor is properly mounted.  No window on the receiver, but I do have a sight glass in one of the lines.  It shows bubbles with the system off, and very little if any bubbles with the system on.  Someone suggested spraying a mist on the condenser while watching the gauges.  This lowered the gauge readings significantly and also brought the register air temp way down temporarily.  I'm beginning to think I have a condenser airflow issue.  This might explain the engine near overheat situation when using the A/C.

If you can see bubbles in the sight glass with the system operating and stabilized, you're a little low on freon.  An internally plugging condensor will cause the high pressure to increase and the low pressure to decrease.  As you probably allready know, the condensor's job is to turn that high pressure gas into a high pressure liquid thru thermodynanic action(airflow). If you have to change it, be sure to change the drier and purge the lines at the same time. Birch has some real good info in his last post and I'm in complete agreement with all he's saying there. 160 thermostats in the summer are a good idea - IMO.  You should be running a fan shroud if you're not, and at least a 3 row radiator (4 is probably better for your application since you have that AC condenser out there in front of the rad airflow). good luck in your efforts.jlg