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Re: ACbrrr monitoring

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On 3/31/2017 3:08 PM, Neon John wrote:
> On Thu, 30 Mar 2017 14:31:35 -0700, Don Y
> <blockedofcourse@foo.invalid> wrote:
>
> As an engineer who has operated an industrial/commercial refrigeration
> business on the side for most of his career,  I'll take a shot.
>
>> What can I learn (in absolute and relative terms) from monitoring
>> the temperature and pressure in high and low side coolant lines
>> to the ACbrr's evaporator coil?
>
> I have no idea what "ACbrrr" is but I'll guess that you're speaking of
> the HVAC on a modern car.

No, in a home (modern or otherwise)

> The answer to your question is essentially "absolutely nothing".  An
> extreme lack of refrigerant will manefest itself as little to no
> cooling but you'll probably have already gotten a CE light by then.
>
> If you are low on refrigerant you can't just "dump in a blow-off can"
> and hope for the best as in the old days.  The system should be
> drained, evacuated and charged to the nameplate weight of refrigerant.
>
> The reason I said "absolutely nothing" is that a modern car may have
> all or part of the following:
>
> computer controlled expansion valve
> computer controlled or not evaporator back pressure regulating valve
> (GM parlance: POR valve)
> computer controlled or not variable displacement compressor
> computer controlled variable speed condenser and evaporator fan.
> high and low side pressure and temperature sensors.
>
> All of this sophistication is in an effort to squeeze that last
> hundredth of an MPG CAFE rating.

But that's NOT the case in homes.  And, I suspect far more energy is
expended cooling tens/hundreds of thousands of cubic feet in a home
than the hundreds of cubic feet in vehicles!

*Businesses* have additional instrumentation (available) on their
HVAC plants.  But, that hasn't manifested in the home, yet.

I've seen studies estimating that "the vast majority" of home plants
are operating 10-20% below their expected level of efficiency.
Why buy a 12 SEER unit and operate it at the efficiency of a 10?

The "concerned homeowner's" only remedy is to call a heating/cooling
contractor and HOPE you get a tech who knows more than just
rule-of-thumb guidelines.  (And, you can almost be guaranteed
that he'll say you need *something* done, now that he's made the
trip!)

OTOH, if you have instrumentation that can watch the (HVAC) system
ALL THE TIME (in much the same way that an automobile does -- and
for similar reasons), then it can notice trends and advise the consumer
(with more than an "idiot light"):
- "Please replace the air filter in your furnace blower"
- "Please clean the condenser coils"
- "Please call a service man to clean the evaporator coils"
- "The running current on the compressor has steadily increased
   to a point suggestive of imminent failure.  Please call for service"

(e.g., "Click here for a sample video illustrating how this is done")

It can likewise note when a plant has been poorly sized and adjust
the control algorithm to enhance comfort *or* increase energy efficiency.

"Human beings" don't seem well suited to these sorts of activities,
unaided/unadvised.

> The car's computer (known as the PCM or powertrain control module) can
> take measurements and compare them to built in models to determine if
> the CE light should be lit.  The dealer's diagnostic console can set
> up standard conditions and do more rigorous testing.  You can't do
> that as a user.
>
> In the old days, I'd fully load the system by either opening the doors
> in the summer or putting a couple of 240 volt heaters in the front
> seat in winter and then look at the evaporator superheat to begin with
> my testing.  The back pressure regulating valves spoiled that method.
>
> Another method that I use that I've never seen used anywhere else is
> to don a mechanic's sthethescope and then press the probe HARD against
> the expansion device.  Stressing the diaphragm acts as a high pass
> filter and eliminates most of the engine and compressor sounds.
>
> I can then listen to the flow of the refrigerant through the expansion
> device.  With plenty of refrigerant, it sounds like water flowing in a
> pipe.  With a large lack of refrigerant, only the sound of gas flowing
> will be heard.  If the charge is intermittent and/or on some vehicle
> system designs, a mixture of fluid and gas bubbles can be heard.
>
> One has to carefully mix gauge readings, expansion device sounds,
> temperatures and experience to figure out the system status.
>
> One technique I use is to charge about an ounce of refrigerant and
> listen to the change in sound of the expansion device.  If it doesn't
> change and the sound is that of a mixture of bubbles and fluid and
> everything else seems normal, I usually conclude that the system was
> designed to operate in starved mode.
>
> The most difficult to diagnose is a worn but not failed compressor.
> I'm not a "parts changer" so I try to diagnose the compressor by
> varying the load (heaters in the cabin) and comparing the pressures
> and temperatures to the compressor OEM's charts.
>
> Given the declining quality of high school grads that make up most
> HVAC shop employees, few shops attempt much in the way of diagnosis.
> They'll evacuate the system (for which you're charged an environmental
> recovery fee while the company sells the used refrigerant for
> recycling), change the expansion device and the filter/dryer and
> recharge the system.  If that doesn't fix the problem, out comes the
> refrigerant again (another fee) and the compressor gets changed.  If
> that doesn't fix the system, the tech punts to the shop owner who
> usually does have a clue.
>
> Some enterprising techs will actually check the condenser to see if it
> is dirty and needs cleaning.
>
> So the AC system in a modern car is pretty much like everything else
> on the vehicle - if you're not a dealer or have a $4-10k aftermarket
> diagnostic system (plus $1000/year updates), you just can't do much.

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Thread

ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-30 14:31 -0700
  Re: ACbrrr monitoring Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-30 14:49 -0700
    Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-30 15:02 -0700
      Re: ACbrrr monitoring Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-30 15:16 -0700
        Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-30 15:45 -0700
  Re: ACbrrr monitoring Neon John <no@never.com> - 2017-03-31 18:08 -0400
    Re: ACbrrr monitoring Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-31 15:33 -0700
      Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-31 15:53 -0700
        Re: ACbrrr monitoring Neon John <no@never.com> - 2017-03-31 20:36 -0400
          Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-31 19:22 -0700
            Re: ACbrrr monitoring Neon John <no@never.com> - 2017-04-01 12:18 -0400
              Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-04-01 11:17 -0700
                Re: ACbrrr monitoring Neon John <no@never.com> - 2017-04-02 12:26 -0400
                Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-04-02 14:42 -0700
    Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-31 16:06 -0700
      Re: ACbrrr monitoring Neon John <no@never.com> - 2017-03-31 20:53 -0400
        Re: ACbrrr monitoring Don Y <blockedofcourse@foo.invalid> - 2017-03-31 19:38 -0700
          Re: ACbrrr monitoring krw@notreal.com - 2017-03-31 23:11 -0400

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