TimSpencer

Restrictions are likely to be in the receiver/drier(easier to change most of the time) or expansion valve(under dash never fun). Many times you will see frost on the line/ fitting on the leaving side of the drier. Any of the synthetic compressor oils used with R134a refrigerant will clean out the inside piping as it passes through the system. Hopefully collecting in the drier rather than the expansion valve. Have as clean a system as possible before charging is best. There are system flushing agents you use to clean piping and coils before charging.

Low voltage could cause many issues. Including not keeping gas valve solenoid open, poor controller operations and poor draft motor and or blower motor performance. The controller is going to look for feedback from safeties and if the voltage is low it can perceive that as a safety being open. This is why bad or loose connections can cause issues as well.

The “clutch” is an electric solenoid of sorts. When energized it locks belt pulley to the compressor crank shaft to pump refrigerant. When not energized the pulley is just riding along with the belt. You could check continuity of the coil on the clutch and any and all wiring to the clutch. Check for any shorts as well(wires rubbed through, loose connections, etc). You could check amperage on that circuit as well, hopefully no other loads are attached

The oil is in the system unless it leaks out. Same as refrigerant. The oil is likely in the evaporator and condenser coils. These systems have a small amount of refrigerant and if there is a small leak it leaks 24/7 so over a long period of time it will be gone. Vacuum check for small leaks is not very accurate unfortunately. I would reuse the compressor and a new charge of oil, replace the receiver drier, and accumulator if equipped. I would pressure test with nitrogen ( nitrogen also helps dry the system) leak check then evacuate with a proper vacuum pump. I would try to get to the lowest reading on my gauges ( unless you have a micron gauge). Charge system when vacuum is at lowest. Run the unit and check temps and pressures. Hoses and orings are likely suspects for leaks.

Refrigerant is terribly expensive to use as a test gas and the cost for a “sniffer” leak detector might be excessive for a one time use. Easier to pressurize with nitrogen (you will need to buy a regulator) and use soap bubbles to find leaks. Nitrogen can be found at welding supply stores or places like AirGas that sell all sorts of compressed gases. Deposit for a tank, return tank for deposit and contents are very cheap. Regulator can be found online for a good price too. Pressurize with nitrogen, spray hoses and connectors with soap bubbles and look for signs of leaks, fix leaks, check repairs. Much simpler and straight Forward.

Receiver in on the liquid line and will be high side pressure. It stores “excess” liquid refrigerant. As the load on the evaporator goes up and down the metering device will back up the liquid into the receiver. The filter/drier also works better on liquid refrigerant so the automotive industry incorporated all of these into one device for packaging issues. The accumulator will be on the suction line, low side pressure. It’s a tank designed primarily to protect the compressor from any liquid refrigerant or oil slugging the compressor and ruining the suction valves of the compressor. This item is not always used. It’s very common on Heat pumps but straight cooling systems it’s not universal. Automotive units use desiccant in the accumulator but not always. The desiccant is a solid formed “brick” or pressed collection of treated pea gravel looking material. Device usually has a fine screen on the leaving side to collect large particles.

This is a very common automotive/truck filter/drier receiver. Usually has a treated pumice stone as the filter/drier.

Take your time and you will be able to get the system running it’s best. Seems daunting but each step is not very difficult. Air conditioning/refrigeration has been my trade for 30+ years now. Post back with any questions or observations.

You may want to check/clean condenser coil on unit. Driving down the road may have provided extra air flow to keep unit running fine. But while stationary you rely on the condenser fan in the unit and if the coil is dirty or plugged it may cause unit to trip on high pressure. If it’s cycling on temp and then not restating when temp comes back up I would check the start components like capacitor and stat.

First I would search for the leak. Connect your new set of gauges to the connections near the compressor. Try to determine low pressure connection and high pressure connection(blue and red hoses respectively) high pressure hose will go to condenser and low pressure hose to the evaporator(front of coach). Pressurize the system with dry Nitrogen not Air from a compressor, not CO2, and absolutely not O2. First two will add moisture to your system(bad) last one will cause a large explosion. With 100-150# of pressure from your nitrogen. You can use a dish soap and water in a spray bottle to look for leaks. Spray every connection and if it leaks you will see bubbles. Release nitrogen and fix leaks retest if necessary. Once leaks are fixed connect vacuum pump to yellow (center hose). Open all valves (including valve on vacuum pump) and start pump. Watch gauges and both should start to go into a vacuum in the gauges. Get it to the lowest point on the gauges (29.9”WC) may take a few hours. Once you are at or near the pin. Close all valves on gauges and have cold one. Pressure should hold. After an hour or two if it’s good you can start to add oil and or refrigerant. Oil can be “sucked” into the low side fitting of compressor. Yellow hose in oil container or if using pressurized can connect to yellow hose and only open blue side valve and oil end up in suction portion of compressor which is open to the oil sump. Be careful not to suck “air” into the system. Then you can start to add refrigerant. I would close all valves and add refrigerant to the high side, red hose. If you are sure of charge amount try to add all of it at this time. Close all the valves again and start the engine be sure you have max air flow across the evaporator(dash) coil and condenser coil(usually near radiator) fan for condenser maybe needed. Turn system to full cooling and monitor gauges and operation of the clutch on the compressor. Now that you have pressure on the system it should lock the clutch and turn the compressor. Monitor the pressures and temp of the air out the dash. Convert pressure to temp(numbers in multiple colors on gauges). For this type application you want 40*F on the blue(cold) and 100*F on the red(high) side. R134a roughly 35#,125#. only other suggestion would be to replace the “filter/drier” if the system has been open (leak) for an extended time. It may clog up once it’s been running for a while if there are to many contaminates in the system. I would also be sure you have a separate and specific fan for the condenser coil as this seems to be a common issue with these systems.

The fan on the condenser is going to be your issue. As soon as you turn on the dash air the condenser will need full air flow. Best way to ensure that is to have a separate fan just for the dash A/C condenser. If you had an obstruction in the system the pressure would level off and compressor would cycle off on low pressure once the refrigerant was stacked up behind the obstruction. Personally I would add an electric fan attached to the a/c condenser and have it triggered by the clutch on the compressor (going to need a pilot relay). Derale and others make inexpensive and powerful models. Or add a high pressure cutoff switch to prevent compressor from reaching blow off/ relief pressure. Or better yet both for added security