Las Vegas, Amana Split HVAC System (qty 2), One stopped but now working

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Reader90

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Hello,

Systems:
1.
I have two identical systems (Amana-ASXC160601-BA, matched to Alpine A Coil CB60D442107000, and Air Handler/Furnace Amana-AMVC 80905CX). Installed in June 2010.
2. Ducting is in unconditioned attic.
3. Perform maintenance yearly, have systems checked professionally every two years.

Been hotter than usual out in Vegas (and other places I hear). Last Sunday, one of the units just stopped working in late afternoon, i.e. cool air turned to warm. My troubleshooting was call for cool still showed on Ecobee app and Ecobee 3 thermostat, air was still blowing high and app/thermostat showed stage 2. Outside, the fan and condenser was NOT running. Breaker in main panel not tripped, Opened up condenser panel, see 24 volts (and board has LEDs illuminated). Local 240 shutoff fuses good (multimeter check). Turned system to OFF from ecobee app. Checked Capacitor (took it out), it was within spec of capacitor rating. Air-filters were changed 2 weeks ago (changed every 60 days). Ducts were cleaned ~3 years ago. Outside condenser foam/water cleaned in spring 2023. ~ 2 hours had passed by now. I checked to condensate line (also cleaned annually) to see if any water was present, perhaps a tell that the A coil froze - Dry, not evidence of water at condensate line. I decided to turn unit back ON for Cool and unit turned on and started cooling fine. I can only surmise that this unit (my Down Stairs unit) was working so hard that a pressure or thermal switch triggered and shut the condenser unit down.... a good thing....).

Fast forward to today. Everything has been working fine or as expected. However, after lots of reading and Google searches, I decided to look at Delta T data and began measuring supply register teams.

I have results of ~24 hours of measurements in a Google Sheet here:


My high level conclusions from this data set:

1. Consider doing something more to insulate the ducting in the attic or the attic in general. House is 24 years old.. Will be focusing on Master Bedroom ducts first. Read this article located @ Green Building Advisor about an accepted practice to bury ducting in insulation, especially in dry climates like where I live (Article here: https://www.greenbuildingadvisor.com/article/ducts-in-an-unconditioned-attic#)
2. Have the Down Stair system looked at due to borderline supply (Delta T) temps as compared to the Up stair system - perhaps a low charge (but these are sealed systems, so I am skeptical that this would be a solution unless it was never charged correctly)?

Other thoughts or comments?
 

Fitter30

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For a correct reading for delta t temp at filter and 2-3' from evap coil. 18- 23°
With such high outdoor temps condenser coils need to be spotless. Need to pull the top see if the coil is made in two pieces cleaning is a more difficult. Wash inside out then outside in. Do not use such a powerfull stream to bend coils. Coil looks like a porcupine don't use a nozzle thumb over the end.
 

Reader90

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For a correct reading for delta t temp at filter and 2-3' from evap coil. 18- 23°
With such high outdoor temps condenser coils need to be spotless. Need to pull the top see if the coil is made in two pieces cleaning is a more difficult. Wash inside out then outside in. Do not use such a powerfull stream to bend coils. Coil looks like a porcupine don't use a nozzle thumb over the end.
Thanks for the response @FIlter30. A couple of comments:

1. I have not measured at the evaporator coils of both units (yet) as not totally easy to get into those based on the connection mechanics to the air handler.
2. My measurements for Delta T where at a) the return grill using a IR meter, and b) measuring the air team at all supply vents, at a grill fin (not to measure a foot into the vent duct). I assume this methodology is, especially as I have two of the same units and can perform the same measurement methodology for both units.
3. For the outdoor condenser fin condition, they are very clean. As for maintenance, I started do this work myself several years back after witnessing a HVAC tech maintenance procedure to do nothing more than use the garden hose to spray (not hard stream) on the outside of the unit, through the protective metal panels. Me, I take the all sides off and top, use either the PF Cool or Web brand spray foam on both sides of fins, let sit for 15 mins, then rinse off with water. I do this every April/May.
4. I do not recall these units being subjected to so many days of 110+ F temps. For the outdoor condensers, as they are located on the South side of the home and are constantly in direct sun, I have thought about building a temporary canvas shield a 2 or 3 feet above the unit to block the direct sun light. Easy, cheap, and would lower the temp of the outdoor units. I have seen the contraptions that spray water on the fins -- while this would help, I would be concerned of continuous hard water spray over the condenser fins.

I have someone from a trusted HVAC company coming tomorrow as I want to have the refrigerant and pressure checked, on the down unit as the the Delta T measurement I made (as explained above) is barely at 14 degrees difference between average of supply and return (and as compared to other system). If the refrigerant is low, well than that will be another set of questions.
 
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