About a year ago, I installed headers, swaped heads and cam which required removal of the AC condensor.

Upon re-assembly, I pumped down the AC system with a commercial vacuum pump and charged the system with 2 cans of R13a and a small can of compatible compressor oil.

The AC system worked fine for a year but recently it began to freeze up after about 45 minuntes of highway driving.

So I replaced the accumulator/drier and pumped down the system again. Unfortunately, there was a system leak that was not detected until after the pump was on for several minutes. In fact, the vacuum pump shut off and the system returned to normal atmosphere (****!).

Becasue it was Sunday, and I could not obtain another fresh accumulator/drier. So I fixed the leak, and pumped the system down again. When I tried to fill the system, the following occured:

1. The system would only take 3/4 of a can of freon
2. The compressor pump clutch was engaged (AC on, fan max)
3. The low side (blue) pressure reading was in the red-zone - too much pressure
4. The high side (red) was about 100-lbs

*****************

Questions:

1. I assume I can replace the accumulator/drier again and start over without diffuculty; I am presumming the system is FULL of moister and that the evaporator freon valve is freezing up causing the system to read too much pressure.

2. If not, what are the classic signs of component failure when the low side (blue) reads too high? Is this a valve problem?

3. Why does my vacuum pump shut down after about one hour; I checked the oil level before pumping? It seems to recycle and will again pump after shut down but only after it fully cools?

4. Is it possible that the system has too much compressor oil; some of the oil drained from the condensor when it was sitting on the garage floor 12 months ago - this is why I initially charged the system with a small can of compresor oil? If too much oil, I assume using compressed air to force the oil out is a NO-NO becuase it introduces more moister into the system.

Thanks...

 

For one thing, it sounds to me like you had your low and high pressure hoses switched. That is what probably was giving you the unreadable low pressure and the low head pressure.
Your vacuum pump has an internal motor thermostat to protect it against overheating. Either the motor bushings need oiled or you are pumping too many CFM's and overloading the motor. Whatever the cause, your pump motor is overloaded. These need to be able to run for hours and hours because the principles of evacuation call for that, as well as knowing what kind of vacuum your are achieving. And I don't mean how close to 30" you are on the compound (low pressure) gauge.
I just went back and read your posting again. If you had soooooo much moisture that you were freezing at the point of expansion, you would be reading a low suction pressure. Since you are not, and since you cannot put more than 3/4 can in, probably because you are trying to put it in the liquid line, I have to say again that your gauges are hooked up backwards. Boy am I glad in the almost thirty years of being a refrigeration man, I have never done that!!!!
It sounds to me like you are on the right track. Low side hose goes on the larger system pipe usually insulated. High side is the small line or liquid line. I would not worry about another drier. If you are sure there are no leaks, evacuate your system again, for a few hours and if you have something that makes heat (hair drier, quartz trouble light, heat gun) direct that heat at your accumulator/drier. Just don't get things too hot. Just enough to keep it good and warm. Any moisture that the drier is holding can be evaporated and drawn out using the vacuum pump. When evacuating, one should use a good gauge like an absolute pressure gauge or better yet, a micron gauge. These tell you if there any leaks and/or moisture left in your system. By evacuating for a few hours you should be ok provided your vacuum pump is up to snuff. It has to be able to pull a good vacuum in order to get below the boiling point of water for a temperature lower than the ambient temperature in order to evaporate the moisture in your system. If you can evacuate a leak-free system for a few hours with an efficient vacuum pump, and keep the air out of your sytem while charging, your system should be fine. It was before wasn't it?

 

Walley:
Thanks for the info; I used to work on AC in the 70's and it has been a LONG time since then. Your help is very useful.

I'll re-check the guages again. Since the hardware for each colored hose connection is designed to allow connection to EITHER the high or low side but not both, I assume you mean that I could have attached the wrong colored hose to the wrong valve on the guages and that my high side guage pressure reading is really the low side guage pressure reading and visa versa - right?

If this is true then, I'm not sure how I could be be installing the freon charge on the wrong side of the system?? Just to make sure I'm clear:

For evacuation of the system:
1. the vacuum pump is attached to the yellow line (middle) on the guage - after the old freon charge is released (motor - off)
2. The red and blue lines are connected to the high/low sides (the fittings only work on the correct high and low sides - right?)
3. the pump is turned on and BOTH the high and low guage valves are opened to evacuate the entire system (this produces negative readings on the guages which is the normal vacuum - right?)

Charge the system with freon:
4. I close both high and low valves on the guages and only then shut the vacuum pump off
5. Disconnect the yellow line to the pump and install the freon feeding tube with the pin to the yellow (middle) line
6. Start the car and turn the AC and AC fan on max
7. open the freon can with the pin and then open BOTH high and low guages.


The confusing part about your message is that you believe I may be installing freon into the wrong system side. Since both valves on the guages are open during the charge, I thought this was not possible.

Any thoughts on why the AC would shut down after about 45 minutes of highway driving - I thought it was moister contamination with the freon valve freezing up but perhaps it could have been a faulty switch??? Low freon would not do this right?

Is the valve inside the accumulator/drier? On the 70's systems the valve was always separate from the drier - somewhere near the evaporator.

Your recommendation on getting a better vacuum guage is good; where can you buy these? I'm not sure there is any way to regulate the vaccuum on my pump, however. It does have a valve that I believe is fully on or fully off - it turns 90 degrees - is this used to vary the vacuum? The pump directions are not clear on this point.

To avoid overheating the pump, I suppose I could vaccum for a few minutes, turn the valves off and shut off the pump for a while and then continue after a few minuites of cool down; this seems combersome but I suppose it could be effective in avoiding a overheated pump. Back in the 70s we used to leave the pump on overnight with no problem - the new pumps are much more sufficticated, however.

Thanks for all your help!

 

You're lucky you didn't blow your *** up. You keep the high side valve closed on the manifold gauges and only open the low side valve when charging. By opening both valves, you connected the low side, high side, and the can of freon together. The high side liquid was given a path to enter both the low side and the can. Are you sure you used to work on A/Cs?

 

Your pump should not be overheating and shutting off. When a pump is first put on a system, it draws higher amps because of the amount of air it is moving. After awhile, the air flow slows and the amps drop down. No one really watches the amps that a pump is drawing, but yours sounds like it is overheating and high amperage means heat. You can try throttling back on that valve you mentioned to cut back on the airflow. You can also lay a damp rag over the motor and keep the rag damp. The evaporating water will cool the motor. Water transfers heat faster than airand evaporation is even quicker. What kind of pump do you have and does it have a gas ballast vent valve? On the portable pumps, it is usually on top and is a knurled **** with an o-ring. When you open this valve, you can hear the pump load up. When you first begin evacuating a system, the gas ballast should be open to bypass the vacuum pump oil and thus saving it for later. The ballast should then be closed after the system reaches 1000 microns.
A Supco VG-60 is an LED display of deep vacuum from 50 to 5000 microns. I am not sure where you would be able to buy this. I guess do a search and try online or if you know someone who does refrigeration, you can get it at a refrigeration wholesaler.
The connections at the end of your hoses will only go where they are supposed to. I did not know you had both valves open when attempting to charge. After the system is evacuated and the new can of R134A is connected and opened, loosen your yellow (middle) hose at the gauge manifold to purge the air from it. Now you are ready to charge the system. You can turn your can upside down and charge liquid directly into the liquid line (high side) or small line, without the compressor running, by opening just the high side valve. The proper amount of R134A is stamped somewhere in the engine compartment. Charging this way, you will have to guesstimate the amount you are putting in. After this can is "empty", shut the high side valve and put on another can and remember to purge your line again. The purging process is only necessary if your hose does not have a shut off on the end to keep refrigerant from escaping when it is removed from a tank.
The rest of the charging has to be done through the low side only, while the compressor is running. This keeps the pressure in the system lower than the pressure in the can and allows the refrigerant to flow into your system. By having both valves open, you're bypassing your system low side and dumping liquid into your compressor. Not good. The high side pressure would also keep you from being able to empty the refrigerant can.
Once it is fully charged, try it. What exactly was it doing after the 45 minutes or so? There is a low pressure switch that will shut the compressor off if the system pressure does get too low. Higher speeds equal higher RPMs of the compressor, so it does pump faster and will produce a lower pressure, but it should not be low enough for your pressure switch to open. If it does, either the switch is bad, you are low on charge, or you have a slight restriction that is showing up at high speed. The latter is not too likely though. They do not use an expansion valve anymore. There is an orifice with a strainer just before it. This is located somewhere between the drier and the evaporator in the liquid line. I don't do automotive AC by trade, but the principles are the same, just different things to look out for.

Rots of Ruck,
John

 

Wally:
OK thanks - I'll try your refill method after I vacuum once more.

I guess I will not replace the drier again; I'm sure there is some moister in the system now, however, since during the first evacuation, the low side connection to the drier was not fully closed (wrong o-ring was used while the pump was on for 15 minutes or so). As indiacted above, when the pump overheated and shut off the system returned to normal atmosphere (****).

During the second evacuation, the pump overheated and shut down prematurly - after about 30 minutes. Since the connections in the system were secure the second time, the vacuum was mantained after the pump shut off.

The pump does have a gas ballast valve on top which I have been using according to the instructions. I will (i) try heating the AC drier when evacuating, (ii) use a damp rag to cool the vacuum motor and (iii) cut the vacuum using the 90 degree valve.

Ideally, I would like to run the vacuum for a few hours.

Question: Am I trying to keep the electric pump MOTOR cool or the pump MECHANISM cool - placing a damp rag on the motor sounds a tad dangerous since it has air cooling vents on one side??

One other mention. When I was using the pump this time, I used a 100 foot 115V extension cord. 12 months ago, the car was parked closer to the garage and I used a 50 foot 115V line and I did not have the overheating condition. Would the use of a long extension cord cause the vacuum pump to overheat? The house circuit-breaker did not trip when the pump shut down twice on Sunday, however.

Thanks again!

 

Oh yeh, you also asked what the car was doing when the AC would shut off 45 minutes into a highway drive. This happened several times.

Well the AC was cold and then only hot air came out of the vents. I thought it was a blown compressor clutch fuse but the fuse was OK. I would then keep driving but I would turn off the AC for a few miunutes. After a while, I would turn the AC back on and it would blow cold again.

Weird huh?

 

You need to cool the motor. It is the thing drawing the amps. It is possible that your cord is too small and too long. The wire size might only be 16 ga. Voltage drop causes a rise in amperage which is heat. Rather than trying to cool the pump motor, move the car closer to a sufficient outlet. Running on low voltage is very hard on equipment. Evacuate it for as long as you can. Hours is the next best thing when you do not have a good vacuum gauge.

John

 

OK great - thanks for all the help!

 

...the system is now pumping down...apparently, the 90 degree valve on the vacuum pump is proportional and varies the amount vacuum ...the instruction manual does not indicate this fact, however...

 

I pumped down the system again and refilled it as instructed.

AC works great now..

We really need an AC topic on this board!

Thanks....