A/C low pressure side cycles high and low

Did you just top up the gas or dehydrate the system and recharge? From what I can see you have a blockage in the system causing it to pump down,probably moisture forming at/in the TX valve.
I would dehydrate the system properly and then charge it up again.

 

TX valve is the thermal expansion valve.It may not be faulty but it appears to be giving you the fault.If you have moisture in the system,this moisture may find itself at the valve and it can form ice which would block the orifice,causing the sudden blockage and pumpdown symptoms which results in the pressure on the suction side to drop down so suddenly.

I would remove/decant all the contaminated gas and dehydrate the system properly then recharge.

 

Wade. The fact that the compressor pumps the low pressure/suction pressure side of the system down to "zero" means that your compressor is trying to suck the refrigerant back to the compressor(intake). That is a good thing.

The system low pressure switch located on the filter/dryer (under the front hood) on a Mondial shuts the system off/electrically disengages the compressor clutch when the pressure is below the low pressure set point of the switch. Typically, that would indicate you need more refrigerant in the system, if there are no other problems/issues in the system.

It is true that a plugged TX valve could cause a similar low pressure cycling situation. If your system was working OK before, I doubt that is your problem. The TX valve in located under the dash on the passenger side. It is on the upper right side front corner of the A/C box. Hard to see, but it is there.

The TX valve control bulb is attached to the suction (large) refrigerant copper line near the same location. Look up some google images for a TX valve and you will see the valve and the control bulb. The valve controls the liquid refrigerant passing into the evaporator coil, and the bulb controls the valve opening size.

The TX valve is located in/on the liquid refrigerant copper tube and the TX valve controls the amount of refrigerant entering the evaporator coil based on the temperature of the suction line refrigerant coming out of the evaporator. The TX bulb detects the temperature of the suction line refrigerant in the suction line. The warmer the bulb the more refrigerant the TX valve allows into the evaporator coil. The cooler the suction line the TX valve allows less refrigerant into the evaporator coil.

Because you do not have a pressure gauge on the discharge side (high pressure) of the compressor, it is hard to determine exactly what your system is doing. I would guess that your discharge pressure is also very low while the compressor is running. This would be another indication you need more refrigerant in the system.

You can also look at the sight glass in the top of the filter dryer. If you see gas bubbles while the compressor is actually running, it is another indication that you need more refrigerant.

How did you decide how much refrigerant to add?

I will say that the cycling symptom is a typical recharging dynamic until a sufficient amount of refrigerant is added to the system.

I am not sure amount the clacking sound, but the clutch makes a loud click when it engages. It is a metal on metal clutch. The metal friction drives the compressor.

Also. if the system has some static refrigerant pressure before you added the refrigerant, it is unlikely any air and/or moisture entered the system. In other words if the system had more internal pressure than ambient atmospheric air pressure - the system would not suck air or moisture into the system. I know there are some arguments to be made on that statement - but for this issue it is OK.

Good luck.
Jerry
DRG

 

The pressure is supposed to cycle under low A/C loading conditions. Your low side pressure switch, which should turn the compressor off as it pumps down to about 25PSI is not working consistently. The video shows it working sometimes, and sometimes failing to shut off for a while. When the pressure can get below 25, the evaporator will ice up. The pressure cycling valve can be replaced without removing the freon in many systems, but I don't know about yours in particular. The compressor probably does not like operating at 0 PSI as its lubricating oil is transported by the freon and at zero there is no transport.

If the pressure was almost zero when you started and the system was off, it is likely you started with very little freon in the system. You might not have enough in there still. Best is to evacuate and refill by weight, but that involves a tech.

Fix the leak, replace the pressure switch, and fill correctly. It'll go back to cooling as well as it ever did on R134.