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Old 07-31-2012, 11:08 PM   #91
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Adding R-22 increases suction temperature???


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You should calibrate all of your hygrometers.
The hygrometers I have are the inexpensive (<$10) analog, dial-type that you might find in a cigar humidor. I have a digital one ordered. It has shipped and should be here within the next couple of days.
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Old 07-31-2012, 11:20 PM   #92
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Adding R-22 increases suction temperature???


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Ah! You are correct. I made a mistake.... imagine that, and I had such a perfect record.... Thanks for pointing that out to me.

I am finding these new gauges harder to read than my old ones, because the low pressure gauge goes all the way up to 500 PSI (to protect the gauge from damage by high pressure) while my old ones only went to 150 PSI, so the resolution is not as good with the new gauges.



Actually the superheat is higher than I posted.


Should have posted
  • Suction Line psi/temp: 65/37
  • Suction Line temp: 45
  • Superheat: 8

I just checked. Current readings are:
  • Suction Line psi/temp: 70/42
  • Suction Line temp: 50 (still using infrared thermometer)
  • Superheat: 8
  • Wet-Bulb: 65
  • Required Superheat: 8 per Payne chart, 10 per the formula
  • OAT: 95
So things look pretty good. However, I will do as you suggested and remove refrigerant until system is obviously undercharged and then add it back until proper superheat is obtained.
You're 2 degrees off/overcharged with those numbers. Get you some real tools and quit wasting our time!

Just messing with you.
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Old 07-31-2012, 11:39 PM   #93
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Adding R-22 increases suction temperature???


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Get you some real tools and quit wasting our time!
Exactly what I've been thinking.

I was concerned when I started this thread that I might just be a nuisance to your pros, but I think you actually enjoy this.... at times.
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Old 08-01-2012, 12:32 AM   #94
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Adding R-22 increases suction temperature???


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Thanks for the suggestion Doc. Unfortunately I don't have nitrogen; and I just checked with a local welding supply store, and, although they have nitrogen and rent tanks, they don't rent the ~$125 regulator. I'll look into this to determine what other alternatives are available for nitrogen.
Ah! Guess what. I can use one of the regulator off of my oxy/acetylene tanks. I'll take a look tomorrow to determine what adapter might be needed to use it with my HVAC set up.

So this system may get a nitrogen bath after all. I can rent a tank for $6/mo and ~$20 to fill it.
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Old 08-01-2012, 02:21 AM   #95
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Adding R-22 increases suction temperature???


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Not uncommon for the outdoor RH to be lower then the indoor RH in the summer.
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At 70F and 50%RH, the air contains 85.2378 grains of moisture per pound. Heat that air up to 90F with the same 85.2378 grains per pound, and the RH is now only 40.2%
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Actually, thats the way it works in the real world also.

If you take 20f air with a RH of 70%, and heat it to 70F, its RH will only be 9.7%.

The warmer air is, the more moisture it can hold.

You should calibrate all of your hygrometers.
I think I have not been listening to you. I've read your words but not analyzed the meaning. I think I now understand. As an exercise I made the following assumptions and consulted my psychrometric chart.

  • The temperature of the air passing over the evaporator is reduced to below the dew point as evidenced by condensation on the evaporator.
  • Therefore this air is now at 100% RH.
  • Using 55F (typical reading I see from my supply vent) and 100% RH, I consulted my psychrometric chart and determined that the lbs of moisture per lb of dry air would be .009.
  • At 75F cold air return temp .009 translates to 50% RH - agreeing with my sling thermometer - and is higher than the outdoor humidity.


I may be slow.... but (I think) I do eventually catch on.
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Old 08-01-2012, 04:21 AM   #96
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Adding R-22 increases suction temperature???


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I think I have not been listening to you. I've read your words but not analyzed the meaning. I think I now understand. As an exercise I made the following assumptions and consulted my psychrometric chart.

  • The temperature of the air passing over the evaporator is reduced to below the dew point as evidenced by condensation on the evaporator.
  • Therefore this air is now at 100% RH.
  • Using 55F (typical reading I see from my supply vent) and 100% RH, I consulted my psychrometric chart and determined that the lbs of moisture per lb of dry air would be .009.
  • At 75F cold air return temp .009 translates to 50% RH - agreeing with my sling thermometer - and is higher than the outdoor humidity.


I may be slow.... but (I think) I do eventually catch on.
Just for grins I held the sling thermometer in front of the supply vent. The readings were:
  • Dry Bulb: 10C
  • Wet Bulb: 9C

This translates to about 87% RH. Not 100% RH but pretty close.
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Old 08-01-2012, 04:26 AM   #97
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Adding R-22 increases suction temperature???


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Originally Posted by psehorne View Post
Just for grins I held the sling thermometer in front of the supply vent. The readings were:
  • Dry Bulb: 10C
  • Wet Bulb: 9C

This translates to about 87% RH. Not 100% RH but pretty close.
80%RH+/-5% leaving the evap coil is normal. Much higher would generally indicate a low air flow problem.
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Old 08-04-2012, 01:30 AM   #98
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Adding R-22 increases suction temperature???


Just reporting back in since you haven't heard from me in a couple of days.

I picked up a rebuilt Nitrogen regulator from a local supply store. I have a Nitrogen tank on its way to me. Should be here on Tuesday. So I will be taking your advice to flush out the system with Nitrogen after all.

My Promax RG5000 arrived today, replacing the one that was stolen. I installed a new filter dryer on it. I already have all the other equipment that I need (gauges, hoses, recovery tank, R22).

Since a few days ago I removed enough R22 to get the LL pressure down to a tolerable level and my compressor is now out of danger, I will not be doing anything more until the Nitrogen tank arrives. At the time I will remove all R22 and flush with Nitrogen.

I have one question: If I decide to put in new R22 I assume that I will need to add oil separately (before adding R22) because I am under the impression that R22 does not come premixed with oil. I have a tank of R22 that is nearly full, and I haven't needed refrigerant for several years; so after the current exercise I probably won't need it again for years. So putting in new R22 instead of reinstalling the old recovered R22 is not a financial concern for me. There won't be any current out-of-pocket expense. I'm just assuming that there may be some contaminants in the old R22 (even though it will pass through the brand new filter dryer that I installed on the Promax RG5000 today) and that new would be better. Your thoughts? Should I just reinstall the recovered refrigerant, or since adding new is not a financial concern for me, should I install new R22?

Thanks,
Paul

Last edited by psehorne; 08-04-2012 at 08:01 AM.
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Old 08-04-2012, 04:27 AM   #99
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Adding R-22 increases suction temperature???


Reuse the recovered R22.
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Old 08-04-2012, 07:01 AM   #100
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Adding R-22 increases suction temperature???


A filter drier is not a purifier. It's purpose is to it catch heavy particles to prevent your refrigerant metering device from being clogged up.

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Old 08-07-2012, 11:20 PM   #101
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Adding R-22 increases suction temperature???


Reporting in:

Today I received my Nitrogen tank. I had it filled and followed your suggestions.

  • I recovered the R22 into my recovery tank using my Promax RG5000.
  • I removed the Schrader valves.
  • I then introduced Nitrogen into the high side of the system and confirmed pressure on the low side. I then allowed the Nitrogen to flush out the system via the low side port.
  • I then introduced Nitrogen into the low side and confirmed pressure on the high side, and then allowed the Nitrogen to flush out the system via the high side port.
  • I installed new Schrader valves.
  • With 89F air entering the condenser and 61F inside wet-bulb the charts called for 5-7F superheat (depending on whose chart or forula is consulted). I gradually charged the system in steps with 30 minute settling time in between steps and ended up with 6-7F superheat (70psig/41F and 47-48F pipe temperature).

I plan on checking it in a couple of days.

Thanks for all your help.

Last edited by psehorne; 08-08-2012 at 03:02 PM.
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