High temperature and pressure in air compressor

There are several reasons for a compressor to run too hot, including high compression ratio, high return gas temperatures, and lack of external cooling. High compression ratios are the result of either lower than normal suction pressures or higher than normal discharge pressures.

If it is the sort of compressor that needs oil (lots don't), you won't do better than obtain a can of dedicated compressor oil as produced by most respectable oil companies.

Compressors don't operate at such high temperatures as engines or suffer such extremes of pressure as hydraulic oils and so it is best to use an oil formulated for the conditions found in a compressor.

If you temporarily can't source a dedicated compressor oil I suggest you use a straight grade oil; SAE 30 would be about right for hard use but SAE 20 for short runs and light use.

Yes, well somewhat normal. The refrigerant leaves the compressor at high temperature and flows through the condenser coil where it cools about 20 degrees warmer than the outside air flowing through the condenser. Many small air conditioner units use a small copper tube (capillary tube) of a specific diameter and length for that system to cause a decrease in refrigerant pressure between the condenser and the evaporator. The refrigerant leaves the compressor as a gas at high pressure, cools in the condenser and changes into a liquid. The liquid flows through the cap tube and cools more as the pressure decreases and gets closer to the evaporator. The refrigerant boils and evaporates under the low pressure of the evaporator and turns back into a gas. That gas is pulled back to the compressor.
If the condenser is not cooling the refrigerant enough, the tube can become extra hot. Efficiency is reduced. Actual temperatures throughout the system depend on the type refrigerant used, suction and discharge pressure at the compressor, outside and inside temperature. Tables, charts and graphs for various pressure-temperature relationships can be found in refrigeration books and chemical web sites.

The level of overcharge will dictate the severity of the possible problems. The most common problem with overcharging is creating high compressor head pressure which over-amps the compressor motor which waste energy and shortens compressor life. Installed high pressure safeties will usually shut off the unit off and must be manually reset. High system pressure also results in higher evaporator temperatures and higher air discharge temperatures. Grossly overcharged systems could return liquid to the compressor, destroying it.

If you have a split unit, it is fairly simple, just feel the small refrigerant line coming out of the unit. The temperature should be warmer than the surrounding air. If is not running the temperature will be the same as the surrounding air. If you have a package unit, take off the access cover to where the compressor is located. Find the compressor discharge piping to the the condensing coil. It is the smaller of the two major pipes on the side of the compressor. Be careful the temperature of line coming out of a properly operating compressor will be hot enough to cause second degree burns. If the line is very warm to very hot the compressor is running. If you have a set of gauges, attach the RED hose to the high pressure service connection and the other low pressure hose BLUE to the bigger pipe low pressure connection. Make sure the gauges are isolated by shutting the valves. The pressure difference between high and low pressure is normally at least 150 psig diference.

Simply it's a valve in a refrigeration system that controls or meters how much coolant is allowed into the evaporator.
A thermal expansion valve (often abbreviated as TEV, TXV, or TX valve) is a component in refrigeration and air conditioning systems that controls the amount of refrigerant flow into the evaporator thereby controlling the superheating at the outlet of the evaporator. Thermal expansion valves are often referred to generically as "metering devices".
A thermal expansion valve is a key element to a heat pump; the cycle that makes air conditioning, or air cooling, possible. A basic refrigeration cycle consists of four major elements, a compressor, a condenser, a metering device and an evaporator. As a refrigerant passes through a circuit containing these four elements, air conditioning occurs. The cycle starts when refrigerant enters the compressor in a low pressure, low temperature, gaseous form. The refrigerant is compressed by the compressor to a high pressure-and-temperature gaseous state. The high pressure-and-temperature gas then enters the condenser. The condenser precipitates the high pressure-and-temperature gas to a high pressure liquid by transferring heat to a lower temperature medium, usually ambient air. The high pressure liquid then enters the expansion valve where the TX valve allows a portion of the refrigerant to enter the evaporator. In order for the higher temperature fluid to cool, the flow must be limited into the evaporator to keep the pressure low and allow expansion back into the gas phase. The TXV has sensing bulbs connected to the suction line of the refrigerant piping. The sensing bulbs give temperature readings to the TXV to adjust flow of refrigerant.[2]
http://en.wikipedia.org/wiki/Thermal_expansion_valve

There are actually several conditions that could be causing your compressor to draw excessive amperage. If the system is low on its refrigerant charge, the compressor will draw less amps than normal because it is not working as hard as it would with a full charge so low refrigerant is probably not the problem. It is true that the refrigerant vapor being drawn into the compressor is used to cool the windings and if the windings are not cooled it will overheat and trip an internal protective device, but it will not draw high amperage. If there is a problem with the voltage causing it to be lower than normal, the compressor will draw more amperage. A lower than normal voltage is rarely to be found though. If air or some other noncondensable gas has been introduced into the refrigerant system, higher than normal discharge pressures will exist and the expansion device that meters the refrigerant into the evaporator coil (the indoor coil) will not works as it is supposed to. If someone has recently accessed the
glp-1 elisa kithttp://www.cusabio.com/bio1-G-GLP961-7-3.html refrigerant side of your system, it is possible that they allowed some air from their gauge manifold to get in by neglecting to purge the gauage manifild or the hoses properly, but air will not normally just work its way into the system without someone actually putting it in. The most likely cause for the excessive amperage is a dirty condensor coil. When the coil becomes dirty, as it is wont to do, the coil has a more difficult time allowing heat to transfer out of the refrigerant into the air that is being drawn over it by the condensor fan. The normal design of a condensor coil is for the refrigerant to give up its heat content and begin to condense into liquid form at a temperature about 30 degrees above the outdoor air temperature (that's for a standard efficiency coil, a high efficiency coil does it at about 20 degrees above the air temperature). The pressure that the discharge gases are at is directly related to the temperature it is going to condense at. The higher the temperature, the higher the pressure. For a system using R-22 the design characteristic is for it to condense at 125 degrees F on a 95 degree F day. That means that the pressure will be approximately 275 psi. If the coil is dirty it will have a more difficult time allowing heat to transfer out into the air and the condensing temperature will be more than the 125 degrees F. That means the discharge pressure will be higher. The higher the pressure, the harder the compressor will have to work and the more amperage it will draw. The compressor has a built in protective device that is temperature sensitive. As more amperage is being used the temperature of the windings will be higher. If that temperature goes high enough the internal protection will open. Many systems also have a high pressure cutout installed. If the discharge pressure becomes too high, the cutout opens and shuts the compressor off. When the compressor turns off, the pressures on the low pressure side and the high pressure side will equalize slowly. The high pressure condition will go away. Many systems have what is called a lockout protection feature for some of the faults they can experience. Lockout conditions are normally reset by turning off power to the system and then turning it back on. Since the high pressure condition has gone away because of the equalized pressures, the system will start up again, but the discharge pressure will quickly build back up and trip the high pressure cutout again. Condensor coils can be cleaned very easily. Turn off the power to the unit. Using a 5/16" nut driver, remove the screws that hold the condensor fan cover in place and lift the fan and that shroud up and away from the unit. There will be several wires running to the fan motor, but you should be able to raise the motor out of its well so that the inside of the coil is exposed. Take a garden hose with a spray nozzle attached and wash through the coil with it. Try to make sure that the stream of water strikes directly into the coil, not at an angle. The fins are made of aluminum and they will bend easily if the water stream is striking them at an angle. The dirt and debris that has acculated in the coil will be flushed out, increasing the coils ability to transfer heat and work at the proper pressures. There are coil cleaning solutions that can be purchased to assist in cleaning the coil. Condensor coil cleaning solutions arre mixed with water to dilute them (one part cleaner and 3 or 4 parts water) and then sprayed onto the coil with a hand pump sprayer like you would use in the garden. The cleaner solution will foam up after it is applied and will help to fluch out the dirt and debris. The solutions are made with either an acid base or an alkyline base. You may be able to find condensor coil cleaner solution at Lowe's or Home Depot. You can certainly find it at most hvac parts supply houses such as Johnstone Supply, United Refrigeration, RE Michels, CC Dickson, MIngledorf's,

"Hi" means your compressor has gone off on a high temperature limit. Basically, your outdoor coil is dirty and needs to be cleaned or your outdoor fan has stopped working. An air conditioner works off a simple principle of removing heat using a low temperature and low pressure refrigerant. Your compressor does what it is called. It changes that low temperature, low pressure refrigerant into a high temperature and high pressure refrigerant. Your outdoor fan blows over that high pressure gas and it blows out hot air. First thing to check is to turn your unit on, and go outside and feel if you have any air blowing out the back. If you don't, you have a bad fan. If you do, you need to clean your coil. Spray some simple green on your outdoor coil and let it sit for about 15 minutes. Then grab a hose and under low water pressure, wash out your coil from top to bottom pointing the hose in a downward direction. You do not want to point the hose straight into the unit. Make sure you disconnect the power and allow it a couple hours to dry before you plug it back in. If it's just a dirty coil, you should be good to go after that!!

3 stage? It sounds like the first stage has a leaking valve, possibly second stage also - this would explain both the high temperature in stage 1 and the poor pressure from the final stage. Take a look at page 6 of the following link. This is the typical intake and outlet valve diagram for each stage. Valves #2 are intake valves, and valves #6 and 7 are discharge valves. They all perform like check valves, each valve allowing air flow in only one direction. It sounds like your valves are leaking between 1st and 2nd stages. Possibly debris in the valves, or valves damaged. Try taking air intake filter off and check for damage to air filter and debris at intake. Also try removing valve plates and check for debris/damaged valves on first and second stages.

http://www.irservicenet.com/filestorage/SCD-749_.pdf

The shut off and on is controled by the limit switch. There is contacts that springs pull down to contact there mating surfaces,the air builds up and over power the springs and lifts them up to shut off. So yours has maybe sparked enough to fuse together or someone has turned the adjusting nut which tightens the spring so it takes more air pressure to shut off. Make sure it is unpluged and remove the cover from the limit switch and look inside the cover for adjustmet instructions. Also check to see if the contact points are stuck together.