HELP! Compressor not staying on when too hot outside

[PatrickJohnD]

I have a 220 volt window unit that works great and cools my entire home, except when the temperature and humidity reach over 100 degrees (heat index).

It appears that I have enough coolant, because when the compressor does kick in the unit puts out very cool air. The problem arises when the outside temperature gets too high, which causes the compressor to stop turning on or when it does turn on (very cool air does come out when it's on) it doesn't stay on very long. Eventually it stops turning on at all.

Often times if I shut the unit off for 15-20 minutes then turn it back on again, the compressor will often kick in again for a short time and the unit puts out very cool air again.

Once the outside temperature gets below 100 degrees, then the unit begins working normally again and adequately cools the entire home.

Does my unit need recharging or is there a problem with my condessor that is affected by excessively hot temperatures?

[HayZee518]

air conditioning 101 - the purpose of the condenser is to remove latent heat from the freon medium and cool it down for system use. if the temp is the same as the ambient nothing will happen, if it's hotter then the ambient then cooling will occur within the freon. if the unit is starved of freon then little cooling will take place as it isn't functioning in full capacity. if your unit uses R-12 or 22 you must have an EPA rated service center to service your unit. If you have R-134a and you have full knowledge of refer systems you can probably do the service yourself if you have the proper gauges and refrigerant. mind you the boiling point of r-134a is higher than r-12 or 22. and so the manifold pressures will be higher.

[LazyPup]

Based upon the diagnostic information presented in the post I would doubt very seriously if there is a low refrigerant condition here.

If there was a low refrigerant condition the evaporator would be icing at cooler temperatures and at high ambient temperature the compressor would be running non-stop but the unit not cooling.

The post states that the compressor is cutting out when the ambient temperature reaches 100degF. We must then consider what factors might cause a compressor to cut out.

The most common cause of a compressor cutting out under high temperature conditions is excessively high head pressure, which is usually associated with a defective condenser fan or fan motor.

This is a window unit and the post says that it is blowing fine but the compressor is cutting out. A window unit uses one common double shaft motor to drive both the condenser fan and the evaporator fan, so if it is blowing on the inside it would stand to reason that the fan motor and by extension the condenser fan, is working fine.

Once a window air conditioner leaves the factory door it is anybodies guess where it may end up so it is imperitive that they must be designed to work under any ambient temperature conditions that they might likely encounter under normal circumstances. While most regions would consider triple digit temps above normal in some regions such as the southwestern desert areas 115degF is not uncommon so it then becomes necessary to design the units to run up to 120degF or more.

Now as Hazee has already pointed out in the previous post, the actual working pressures inside the unit will vary proportional to the ambient temperature.

In the trade when we are checking operating pressures we begin by taking the ambient temperature and add 30degF then we consult the Refrigerant Enthalpy chart to determine what the proper boiling pressure is for the type of refrigerant at that temperature. (In fact, the enthalpy charts are printed on the charging manifold high pressure guage).

By example; let us consider an AC with R-22 refrigerant operating at 80degF ambient temperature. We begin by adding 30degF so the conversion temperature is now 80+30=110degF. Consulting the enthalpy chart we find that the correct head pressure at 110degF is 230psi so if the outdoor temp is 80degF we should be reading approximately 230psi.

If the outdoor temperature jumps up to 100degF the conversion temperature is now 100 + 30=130degF and the conversion pressure is now 299psi.

The system is designed to operate up to 120degF and at 120degF the conversion pressure is now 120+30=150degF which converts to 387psi. This is then critically close to the system maximum test pressure of 425psi.

Keep in mind that these are the normal operating pressures if all things are functioning correctly therefore the system must be designed to work at these pressures, however, there are other factors that can severely effect the pressure.

In order for the condenser to condense the hot gas refrigerant back to liquid refrigerant it must have a constant airflow through the coil otherwise the head pressure will continue to rise, and if the head pressure rises the current draw by the compressor motor will also rise proportionally. This in turn increases the operating temperature of the motor and when it exceeds a predetermined set point a built in thermal overload protector in the motor will turn the motor off until it cools. Also keep in mind as the current draw increases it also increase the operation cost of the unit. If fact a dirty condenser coil can cause your AC bill to nearly double.(Note, a dirty coil can cause as much as a 50% increse in operating pressure)

We already determined that the fan must be working so we must then consider other factors that might be restricting the air flow. The second most common cause of restricted air flow is a dirty condenser coil, followed by missing or damaged sheet metal cabinet components, vegation too close to the unit, fences or other structural materials too close to the unit or lawn equipment or personal items stored too close to the unit where they might block the airflow.

A simple visual inspection can tell us if the cabinet is damaged or if there is foreign objects that might be blocking the air flow and we can easily take the appropriate action to eliminate those problems.

This then leaves a dirty coil.

In the trade we use a concentrated foaming coil cleaner which is mixed with water in a garden type hand tank sprayer to make a working stock. While the concentrate is fairly inexpensive it only comes in gallon containers and considering that it is mixed 50:1 it is highly unlikely that the average homeowner would have need of 50gal of cleaning solution.

The good news is that most HVAC supply houses also carry an aerosol can of premixed coil cleaner. To use it you begin by turning the unit off, then shake the can and spray it directly into the coil from the outside. It will come out of the can in a fine continuous stream, but as it begins to react with the dirt in the coil the cleaner will form a thick foam like shaving cream. The expanding foam actually pushes the dirt out of the fins in the coil. In some instances it produces a fine mist that actually looks like smoke, that is to be expected an is nothing to worry about. Let it set for about 30 to 45 minutes and the foam will begin collapsing down again. Some cleaners recommend that you then give the coil a light rinse with plain water. A garden hose with low pressure will do fine but be careful not to spray water on the fan motor.

If you can slide the unit out of the cabinet it is best to take it outside, then wrap the motor with a plastic bag and apply the cleaner, then you can liberally rinse with water without getting the motor wet.

After you rinse the unit allow about an hour for it to dry, then turn it on and it should run fine. Here is a trick I often use to determine if the unit is dry. Take a jar lid and put about a teaspoon of water in it and set it on top of the unti. When the water in the jar lid has evaporated you can be sure any residual water in the AC has also evaporated.

While you have the unit out of the cabinet take this opportunity to oil the motor bearings, then locate the condensate tray weep holes and clean them out to insure the unit will drain correctly when running.

[suprheat]

I've been servicing A/Cs for 29 years and the first thing I usually do with a window unit is pull it out and clean it. 90% of the time this takes care of window unit cooling problems. And I haven't yet been able to clean a window A/C PROPERLY without taking it out and taking it apart. You need to remove the unit, remove the the shroud from around the coil - 50% of the time this usually entails removing the screws that hold the condenser coil in place and carefully pulling the coil out from the shroud only enough to be able to clean it. Care must be taken so as to not kink the refrigerant lines! You can use foaming coil cleaner if you can get it, but 409 or equivalent will work. Cover the motor as LazyPup mentions and I would also cover the electrical controls on the front. I would also clean the evaporator coil and the blower wheel and fan blade - also shoot some water thru the condensate drain to clean it out. Once you put everthing back together you will probably have to tip the unit 90 degrees to allow most of the water to run out. Now is a good time to oil the motor if it has oil ports - use non-detergent light weight oil. Waiting an hour for everthing to dry isn't necessary because the condensate water from the evaporator drains into the condenser section anyhow. So unless you got the electrical controls wet, you're all ready to slap that puppy back in and get cool already!