AC compressor decides when it wants to turn on :wall:

Old 06-26-14, 12:26 PM
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AC compressor decides when it wants to turn on :wall:

I have an issue I'm hoping to please get some advice about; thanks! I don't have that much experience with HVAC but I'm generally pretty handy with DIY. I have an 18,000 BTU wall unit, it's a Friedrich. It is supposed to cool most of a large apartment, and it does a decent job when it's not really hot outside, though it doesn't really cool the entire apartment, but pretty good. I've noticed recently that the compressor doesn't always seem to be on when you would think it should be, and hence apartment isn't always well cooled. For example, often when I turn it on now the compressor doesn't go on right away, only a number of minutes later. And if the compressor is running and I turn it off, and then back on, compressor still won't go on right away. Other times when the unit is on for a while the compressor won't be on also, even though the apartment is definitely not reached the temperature the AC is set on. But the compressor does often turn on, and does cool pretty well. It could be my imagination, but I'm wondering if perhaps lately the compressor has sounded weaker than it used to even when it's on; I'm not sure.

What would be the first basic steps that an amateur could take to attempt to diagnose this issue? I do have a vacuum pump and manifold gauges that are used on a car, though I don't know if that would help. I obviously wouldn't take on anything major on my own, but any advice would be great; thanks!
Old 06-26-14, 12:44 PM
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Your AC has a time delay device built-in which protects the compressor at restart. So if the compressor shuts down automatically or you turn it off. it won't start again until at least 3 or 5 minutes later. Other than that, the unit should be on immeidately if the T-stat calls for cool..
Old 06-26-14, 12:45 PM
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The problem with wall and window units is that don't have the ability to move the air over large areas. A fan somewhere in the room can usually help that. A fan in the doorway of the room that the A/C is in blowing out to the next rooms can be a big help.

Most, if not all, air conditioners have some kind of time delay built into them. This is to allow the compressor pressures to equalize on a restart. That time delay can be anywhere from 2-5 minutes depending on the brand. That delay is activated anytime the compressor starts whether the unit was just turned on or not.

You should be able to set your A/C to do one of two things.....
The fan and compressor come on together when the thermostat calls for cooling.
The fan runs continuously and the compressor cycles when the thermostat calls for cooling.
Old 06-26-14, 12:48 PM
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Many air conditioners have a feature that prevents the compressor from turning immediately on. Some may wait a couple minutes before turning the compressor on. The compressor cannot start if the system is pressurized which can happen if the power blinks or if the owner is clicking the dial on/off trying to make it come on faster... so it waits a couple minutes for the pressure to bleed down before starting.
Old 06-26-14, 12:53 PM
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Check the location of the thermostat, make sure it's operating correctly. Also check the temperature sensing probe, make sure it's not making contact with the coil but rather just slightly in front of them.
If the sensing probe is contacting the coils, it may be falsely reading cold and shutting down the compressor.

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