Help debugging an A/C unit not cooling anymore

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Old 08-24-18, 03:12 PM
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Help debugging an A/C unit not cooling anymore

Hi,

I own a 11 years old HiSeer (I think that's cheap Chinese company) A/C unit.

Model: SHCR-24K-31B
Cooling Capacity: 24 000BTU

I have been trying to take care of it by changing the filter on a semi regular basis (4-6 months, whenever it would seem clogged) and did a regular broom-wipe on the aluminium fins to remove the dandelion seeds when it is the season.

Today I received a notice from my thermostat that it had been trying to cool for a few hours but the temperature has been going up.

The filter was mildly clogged and I changed it, and I see that the big fan on the unit is turning, but clearly there is no cold air coming through.

In the past, I've seen my neighbor had to change the capacitor, but could it be that if the fan is turning? The proper way to check the capacitor is to check if there is a short between each "leg", correct?

I know that another issue could be related to the pressure of the gas inside the circuit, and I read the sticky stating that if this is the case I need to ask for a professional.

1- Is there anything else I should check before I make a service call?
2- With the above information, apart from adding gas, what else could be the issue that the technician would diagnose?
3- When is it better to change the whole unit instead of adding more gas/making a call?

Thanks
 
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Old 08-24-18, 03:18 PM
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You can't have gas added if there's a leak, you must have the leak found and fixed.


Make sure the compressor is running. If it's not, check capacitor, ohm out windings. If you have no knowledge of electrical and tools to test, time to call a pro.

There are meters and check capacitance and resistance used to check capacitor and compression windings respectively.

Normally it doesn't make sense to replace unless the compressor is shot out of warranty or there's a refrigerant leak in the evap coil, or it's like 20 years old.

Don't spend more than 50% of the cost of a new unit on repair at this age.
 
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Old 08-24-18, 04:12 PM
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These ductless units are not serviced like typical split units. Most have diagnostic LED's or set codes on the display with the problem. Your first order of business is to locate the service manual for it. I found little to no technical info for that unit.
 
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Old 08-24-18, 05:27 PM
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Thank you for your quick reply. I removed the breaker from the A/C unit (but am aware that capacitors could still have energy stored).

Make sure the compressor is running.
--> How can I know for sure? I hear (and see) the fan running, and my feeling is that the noise is different than usual so I am tempted to think that the compressor isn't running... but is there another way than just the sound?

check capacitor
I have a multi-meter and can use it to measure the capacitance of the big capacitor, but I can't readily read how many ohms I am suppose to measure (perhaps it is written directly on the capacitor on the side I cannot see..?)

out windings
What do you mean by that?

locate the service manual for it.
I have the installation manual and the wiring diagrams document (although I am not sure which page refers to my unit). See attached pictures and scanned document. I also have a 10mb .tiff scann of the wiring diagrams... its 8 pages of various models diagrams... not sure if its different than the one I already uploaded here (taken from the installation manual I think). If there is a way to share the 10mb document I would.
 
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Last edited by PJmax; 08-24-18 at 06:48 PM. Reason: added enlarged picture of correct diagram
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Old 08-24-18, 06:50 PM
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That unit has two contactors..... one for the compressor and another for the fan.
Is the fan running in the outside unit ?
If the compressor was running..... the larger refrigerant line would be ice cold.
There is a control board there that takes its command from the inside unit.
 
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Old 08-27-18, 04:26 PM
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Yes, the fan on the unit outside is running. How many Farads should I measure on the 2 tabs of the big condenser?
 
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Old 08-27-18, 04:32 PM
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You mean the capacitor for the compressor ? It should be listed on it.
 
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Old 08-27-18, 05:47 PM
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Ok, I managed to dismantle the panel and get to the compressor.

When the central unit requests for cooling, the AC unit's fan starts turning, but the compressor emits a small humm for 4 seconds, then stops for about a minute. Then starts humming for another 4 seconds, and then stops.

So it seems that the compressor isn't running/starting.

Could it simply be the big 50uF capacitor? By the looks of it, its integrity doesn't seem compromised (not exploded) but I am unable to measure it's capacitance with my multimeter that can't measure 50uF.

What does it mean when the compressor hummms but doesn't start? Could it still be the gas pressure? Of the big capacitor?

See pictures below. The last picture is a relay that was added about a year later, I think because they bypassed a circuit board that wasn't working properly so they simply added the delay timer to prevent someone turning on and off the unit.

Any other suggestions?

Thanks
 
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Old 08-28-18, 08:18 AM
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The 50 mfd capacitor is for the compressor. Since capacitors are relatively cheap, I would suggest that you replace the capacitor and see if that solves the problem. I would suggest that you not let the unit continually try to start until you've resolved the problem, as you could damage the compressor if it keeps trying to start but won't.
 
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Old 08-28-18, 09:23 AM
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That "box" in your hand is a "delay-on" relay. It delays the compressor from coming on for 8 minutes after a call for cool. It could be set down to 4-5 minutes. It's wired into the contactor circuit so as long as the contactor is closing.... that delay module is ok.
 
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