I am running R12 and recently replaced the condenser due to a leak. The A/C works but is not as cold as I would expect. The pressures on the low side are 20 to 28 and on the high side 100 to 250. Any ideas on the problem? Thanks...

 

WWWWWAAAAAAAAAYYYYYY not enough cold juice.

 

First of all, was the system pulled into a vacuum before refrigerant was put in?
What refrigerant did you put into the system and how much? R12 has not been sold to anyone in decades.
Is the compressor cycling when its running?
How long does the clutch stay engaged?
With the compressor running, are the suction and pressure tubes coming off the compressor cold and hot?

With the compressor running, those pressure are not really that bad.

 

Yes, the system was pulled to vacuum for an hour before charging. Yes, I put in R12 (2.25 lbs) as I have several cans on hand and just picked up some more at a swap meet. Yes, the compressor is cycling while it is running so the low and high pressures are cycling between the numbers above. I haven't timed the cycling but it is on and off with the pressures above. I haven't checked the temp on the suction and pressure lines but will do that tomorrow. I have noticed that the compressor appears to load the serpentine belt when it cycles on enough so that it tends to make the belt tensioner "rattle". I have replaced the tensioner, the old one rattled very badly but then new one not so much. Too much mineral oil in the system? Wrong orifice tube?

 

Like I said, pressures look good. With the compressor running, low side pressure is normally in the 20-30 psi range. High side pressure can be as low as 100 but will climb when the clutch is turned on and at around 350-400 psi, a high pressure switch will turn off the AC clutch or turn on electric fans to bring head pressure down. As long as there is good air flow across the condenser, it will take a while to get high head pressures. There is also a low pressure switch which will turn off the AC clutch if pressure is too low, usually from a leak.

AC vent temperature not cold enough? As long as the AC system is working properly, AC clutch cycling, AC pressures going up and down as the clutch cycles etc, the only other thing I could think of is air flow across the evaporator. I'm not sure if our cars have a cab/HVAC filter or not. I don't think so. That means dirt, debris, dust, mold etc can plug up the air flow across the evaporator. The evaporator is mounted in front of the heater core. Cold is cold. It's either on or off. If you don't want full cold, you add heat to bring the temperature higher. Water valve or heater damper door not fully closed and allowing heat across the core?

The chances of the orifice valve being damaged is always possible however if there wasn't any kind of catastrophic failure from the compressor, the valve is probably good however there still could be contaminates on the screen restricting refrigerant flow especially if this system is original. Our cars are getting old.

Since the pressures look good, I don't think the compressor is worn out.

Too much oil can cause problems and it usually shows up on the gauges. The only way to know for sure how much oil is in the system is to do a complete flush and refill it. After evacuation, there's still oil in the compressor and accumulator. Only a flush can clean it all out but you would also have to drain the compressor and accumulator. Not sure what the oil capacity is in our cars but if it's something like 8 oz, then changing a condenser, I might add 1 oz. When changing a compressor, they come prefilled with oil and I don't add any.

 

If you're measuring the pressures with the car sitting still, there's not enough air flow through the condenser. EVER. Pressures should be MUCH higher than what you have as a result.

You don't say where you are or what the ambient is. In typical Midwest US daytime summer conditions something like ambient of 85°, RH 60%, and full sun, expect 35 - 40 on the low side with the function on Max Air and the blower on high speed, engine RPM 1500 - 1800 or so. High side might go REAL high eventually so don't leave it like this for very long. Both high and low side pressures will be lower with the car moving, no matter what they are sitting still. If the pressure is consistently below about 30 on the low side, it will try to freeze up, and will do so if the cycling switch happens to let it continue to run. If it cycles driving down the road in hot daytime conditions, it'll work noticeably poorly, and will give you occasional blasts of humid funky-smelling air out the vents.

It should essentially NEVER cycle with the car sitting still in anything like the ambient conditions mentioned above. It may start cycling with a proper charge driving down the road especially at night, but not sitting still in the daytime.

Also keep in mind, AC systems NEVER seal up perfectly. Some are better than others but they all leak. No leak EVER allows refrigerant to accumulate into the system from the atmosphere; invariably, the charge in the system disappears gradually. If you start out with it already on the low side of "ideal", it will exhibit low refrig symptoms just that much sooner, for good reason. It always makes sense to put slightly too much juice in one rather than not enough. (emphasis on SLIGHTLY) That way, over time, the level will approach "ideal" from slightly above, pass through it, and reach a "too low" level eventually; but it will work FAR better for FAR longer in the meantime.

 

In Washington state, temps around 60 to 65, at idle about 1000 rpm. Due to get weather in the low to mid 70's this week so going to play with it again. I might try adding a little more R12. Going to also pull the cover in the engine bay and check for dirt in the evaporator but doubt that is an issue since it is relatively new. I don't really want to pull the R12 to check the orifice tube unless I have to...