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

[bird95134]

Hello,

I have a tech coming out next Tuesday.  Based on observed bahaviour, both 5 Ton units stopped working last Sunday,  i.e. the call for cooling was engaged (Ecobee), 24 volts present at board in condenser units outside, but both condenser units (fan/compressor) stopped within 60 minutes of each other late Sunday.  Granted, it was 116 F degrees.  Checked power circuit breakers and local fuses next to condensers, all good.  Checked capacitors with MM and they were good. 

I shut down, via Ecobee app, both units.  After 120 minutes, turned units back to Cool via Ecobee app and everything turned on and is working as expected.  I checked the drainage pipes to see if there was evidence of water (frozen A coils) - dry.

AIr filters were changed 3 weeks ago
Outside condenser fins are very clean (clean once a year)
Inside A Coil fins were cleaned 2 years ago

I assume there was some type of temp or pressure trigger built into the overall system to shut system down if pressure or temp to high?

Thoughts?

[Admin]

That's hot.  I've never seen pressures on an AC in that heat.  It could be a high pressure switch that trips because of excessive heat and then automatically resets after the unit has been off.  I would imagine the only thing you can do in that heat is spray the outdoor coils down with water.

The tech should also check to make sure the units are not overcharged and that the condenser fan is still spinning the right way.

[bird95134]

Thanks for reply @Admin.  It has been almost a full week since the units stopped working, then started working again after they were off for 3 to 4 hours.  The week has been constantly into 110+ for the week and systems are working and cooling.  I still have a tech scheduled to come out on Tuesday to check out the systems, mostly the pressure as I have checked the amperage on the compressor and condenser fan (look acceptable).  Capacitors are both within tolerance as per the specs listed on the capacitors (and I have confirmed the sizing for these models (Amana-ASXC160601-BA, matched to Alpine A Coil CB60D442107000, and Air Handler/Furnace Amana-AMVC 80905CX).   Unfortunately, all air handler/a coil/ducting is in the unconditioned attic.  Last Sunday afternoon I think was one of the hottest days (116) these units have seen since install in 2010.  Having 110+ temps for so many days has not been normal here and thus why I am seeing more of a "comfort" issue.  I am assuming the systems shut themselves down as designed, as mentioned by @Admin.

Always striving to make my systems and energy usage more efficient, I have started this weekend to use one of my IR temp gauges to measure supply and return temps at different times of the day, e.g. 6/7 am, 1/2 pm, 6/7 pm, and 9/10 pm.  Based on data so far, I am seeing a big impact of heat in the attic on all of the supply temps (basically the data needed for a Delta T measurement).  I will publish my table I have in the next couple of days.  Already seeing ~20% loss between early AM reading and early afternoon (it is 107.6 F outside as of this post, and 119 F in attic. Note, I have Ecobee sensors through out the home and 1 in the attic, on top of one of the air handlers).  20% loss = 20% temp gain (~ 10 degrees) at supply air vents.

Based on data thus far, Systems are working fine and I am loosing a lot of cooling across the ducting.  As it is dry here in NV, I am seeing some articles about adding more insulation to "bury" the ducting.  I think I might experiment with a few runs first (easy to get to).

More to come.

[bird95134]

Here are my first ~24 hour measurements.  I put them on a 2 Tab Google Sheet. 

https://docs.google.com/spreadsheets/d/1LEyD6BBmcPP7kk8XTAnYQ7IOOMqtKdO6Yplzj9QhS5o/edit?usp=sharing

My conclusions:

1.  Up Stair system: Lots of ducting cooling loss, especially in ducts running to Master Bedroom (there are 3) from UP Stairs system.  System is doing pretty good with Delta T measurements.
2.  Down Stair system:  Same issue with cooling loss, but not has much on some vents.  I assume some of the events move to out of the attic to make it downstairs.  However, there are longer runs (Office and Living Room).  System is not performing as well looking at early AM measurements.

Curios to get any feedback.  I probably could group the supply vents and measure to return or toss out the best/worst readings or even get up in attic to take a reading at the A Coil and add to data point.  However, I think my approach and resulting data sets paint a few pictures.  NOTE:  I have done extensive air flow remediation last year by adding mastic mud and caulking at the supply and return vents, and same up in ducting at the air handler.  I also foamed sealed any canned lighting, vent and fan fixtures in the ceiling wallboard.

1.  Consider doing something more to insulate the ducting in the attic.  Will be focusing on Master Bedroom first.
2.  Have the Down Stair system looked at due to borderline temps as compared to the Up stair system.