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Old 08-19-2020, 06:06 PM   #1
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** Home AC with strange gauge readings **


Hello forum!

I am a home owner and I have three AC units at my house, so I got me a fieldpiece manifold to better understand what is going on.
Two of my three units are showing good numbers on the gauge, both are charged with R22.

The third unit was emptied and recharged with R422B 2 years ago by not-really-pros.


Here are some numbers from today:


When system was still and resting for at least 30 min

SLP LLP SLT LLT VSAT LSAT SC SH TSH ODDB IDWB
PSIG PSIG F F F F F F F F F
130,6 130,6 74,7 77,6 79,6 73,6 -4 -4,9 36,6 81,5 77,5
130,6 130,6 74,7 77,6 79,6 73,6 -4 -4,9 36,7 81,3 77,5

Looking at the R422B temp/pressure chart ... shouldnt the pressure reading be higher when its 81,5F outside?



When system running for at least 30 min

SLP LLP SLT LLT VSAT LSAT SC SH TSH ODDB IDWB
PSIG PSIG F F F F F F F F F
66 230 43 83,3 44,7 110,3 27 -1,8 35,7 84,3 77,5
66 230 43 83,3 44,7 110,3 27 -1,7 36,2 83 77,5


I am having a negative SuperHeat.
Liquid line is not hot
Suction line is wet


I have set the fieldpiece gauge to R422B, I do not see what I could have done wrong.
Do I have to calibrate the gauges when I switch from R22 reading to R422B?

Any hekp very much appreciated.
Thanks!


attached
image 1 shows the PSI at low& high
image 2 shows superheat

Last edited by borcherta; 08-19-2020 at 06:20 PM.
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Old 08-19-2020, 06:41 PM   #2
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Re: ** Home AC with strange gauge readings **


Get your post count up to enable attaching images or post on a third party site and use img tags.

130 psi head does sound low.

Did the contractor use a vacuum pump when doing the job?
Having air/moisture in the system may throw off readings. negative superheat is impossible.
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Old 08-19-2020, 07:20 PM   #3
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Re: ** Home AC with strange gauge readings **


The contractor was using a vacuum pump, he might not have purged the hoses though before filling.
He was using a "car gauge" with PSI readings only, he might have over charged it.

The compressor is noisy, but also old.

Thanks!
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Old 08-19-2020, 07:39 PM   #4
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Re: ** Home AC with strange gauge readings **


Do you have a piston or TXV on the evaporator? Filter clean? P/T chart for those of us who still like to use paper maps.

** Home AC with strange gauge readings **-422b.png
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Old 08-19-2020, 07:47 PM   #5
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Re: ** Home AC with strange gauge readings **


Regardless of the outcome of this repair / issue you should start doing HVAC company equipment and installer research.
You can no longer add any R22 to any HVAC system as of the first of this year.
Some HVAC systems can be retrofitted with a replacement refrigerant.
Commercial installations are not affected by this phase out.
I am sure you already know all of this.
And by using "not really pros" you may encounter more problems.
I would start budgeting for replacements as soon as possible.
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Old 08-19-2020, 08:09 PM   #6
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Re: ** Home AC with strange gauge readings **


Quote:
You can no longer add any R22 to any HVAC system as of the first of this year.
This is wrong.

R22 is still legal to use for service and is available, it just can't be manufactured any more.

It's available because there's old stock as well as reclaimed refrigerant. Price is apparently high.

There is no reason to replace a unit just because R-22 production has been phased out especially with drop ins available. There are many other reasons to replace - most units with R22 that are leaking are not worth fixing due to age.
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Old 08-19-2020, 08:11 PM   #7
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Re: ** Home AC with strange gauge readings **


Quote:
Originally Posted by borcherta View Post
The contractor was using a vacuum pump, he might not have purged the hoses though before filling.
He was using a "car gauge" with PSI readings only, he might have over charged it.

The compressor is noisy, but also old.

Thanks!
What was the original problem?

Probably best have everything recovered and start from scratch.
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Old 08-19-2020, 08:23 PM   #8
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Re: ** Home AC with strange gauge readings **


Thanks everyone so far,


please take a look at the attached graphs, I am still very confused about those numbers. The graph covers 1h of running the AC unit.

Image1:
Superheat-subcooling-targetsuperheat in F

Image 2:
Temps in F for suction, liquid and outside dry ball

The "dent" in the numbers around 81-110 in the graphs is due to me test charging the system very shortly.

Thanks!
Attached Thumbnails
** Home AC with strange gauge readings **-sh.png   ** Home AC with strange gauge readings **-temps.png  

Last edited by borcherta; 08-19-2020 at 08:26 PM.
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Old 08-19-2020, 08:54 PM   #9
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Negative super-heat article. If I read it correctly, there can be a perceived "negative" (read on meter) super-heat if unit is a bit overcharged (low airflow too?) and using a blend with a temperature glide. Who knew?


Quote from link:

"When working with a zeotropic refrigerant blend that has “glide” the change from liquid to vapor and vapor to liquid occurs over a range of temperatures and not at a single temperature. When calculating superheat we use the “Dewpoint” and when calculating subcool we use “Bubble Point” the saturation temperature is the range of temperatures between those two points meaning that it could be “interpreted” as negative superheat or subcool when it is actually just in the saturated range. In air conditioning, the traditional R22 and R410a refrigerants do not have any significant glide but newer blends do so it is something to watch out for."


https://www.hvacrschool.com/negative...e-check-tools/


Better resolution 422b chart, easy to see where a negative SH could occur:


https://pressure-temperature.hvac-buddy.com/R-422B

Last edited by 57TinkerMan; 08-19-2020 at 09:04 PM.
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Old 08-19-2020, 09:19 PM   #10
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Re: ** Home AC with strange gauge readings **


422B has a temperature glide of 5*. If you have an improperly adjusted TXV it's possible that you are experiencing a bit of flooding. Interesting read linked below.


https://m9v.7b6.myftpupload.com/wp-c...rt-3-Mar06.pdf
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Old 08-19-2020, 09:50 PM   #11
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Re: ** Home AC with strange gauge readings **


Humor me...better for me than watching the news.


** Home AC with strange gauge readings **-negsh.png
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Old 08-19-2020, 10:24 PM   #12
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Re: ** Home AC with strange gauge readings **


^That makes a lot of sense. With the last component boiling off at at 34F and basically no superheat, i doubt the unit is over-charged in itself, there may be another issue like low airflow.
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Old 08-19-2020, 10:56 PM   #13
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Re: ** Home AC with strange gauge readings **


Thanks, took me a bit to get my head around it but it makes sense to me now. Looking at his coil temps I agree that his airflow is very suspect. Funny, you would never have seen this measuring SH the old fashioned way. As new refrigerants come out I'm debating whether or not to purchase these new gauges. Probably not, I don't do much service anymore and if I run into problems like this, I'd actually have to think.



To the OP, I think your Fieldpiece manifold is doing exactly what it's supposed to. You probably want to see suction pressures in the mid 70's or so. So check, air filter, evap coil dirty, indoor blower speed setting and unit static pressure. You may have duct issues and the system could be overcharged too. You bought a fancy tool and opened up Pandora's Box. Let us know what you find.
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Old 08-19-2020, 11:07 PM   #14
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Re: ** Home AC with strange gauge readings **


Quote:
Originally Posted by 57TinkerMan View Post
Humor me...

Damn, I keep thinking I'll spell "humour" among other words properly.
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Old 08-20-2020, 05:12 AM   #15
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Re: ** Home AC with strange gauge readings **


Recover the 422b, and put R22 back in.
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