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Old 07-28-2012, 10:36 PM   #16
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Adding R-22 increases suction temperature???


Most Paynes have a piston in heating mode. Could be piston or TXV in cooling mode. Need to verify which metering device you have before you do anything else with the charge.

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Old 07-28-2012, 10:37 PM   #17
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Adding R-22 increases suction temperature???


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What I would do is go back and check the system once it's about 85-90 degrees out, using that formula and see where you stand.
It's 89F outside right now. I will lower the thermostat, allow the unit to stabilize, and measure the air temp entering the evaporator. I'll convert that to wet-bulb based upon the RH in the house and will consult the chart again.

My hoses are still hooked to the unit; so I can go outside and see what the pressures are and measure the temps.

Will report my findings.
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Old 07-28-2012, 10:55 PM   #18
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Adding R-22 increases suction temperature???


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Originally Posted by beenthere View Post
Most Paynes have a piston in heating mode. Could be piston or TXV in cooling mode. Need to verify which metering device you have before you do anything else with the charge.
Looks like piston for both modes.
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Old 07-28-2012, 11:06 PM   #19
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Adding R-22 increases suction temperature???


Here are my measurements with the outside temp now 89F:
Air temperature entering the evaporator (dry bulb) ~74F.
Wet-bulb arrived at by calculating from above and RH 38% = 74F.
Outdoor air temperature entering condenser (dry-bulb) 89F

According to the chart on the unit the above results in a superheat requirement of 27F

Other pertinent measurements:
High pressure line gauge reading PSI/temp = 231psi/111F
High pressure line actual temperature = 107F (subcooling ~4f)
Suction line gauge reading PSI/temp = 70psi/41F
Suction line actual temperature = 50F (superheat ~9F too low)
Air exiting indoor vents = 54F
Cold air return = 74 (diff = 20F)

Bottom line:
I am now seeing too little superheat, only 9F.
Suction temp is too low. The chart calls for 68F.
The chart says to add refrigerant. I will do that now, instead of waiting till tomorrow (when it will be 100+F again).

Thanks for everyone's help.

Paul

Last edited by psehorne; 07-28-2012 at 11:27 PM.
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Old 07-28-2012, 11:36 PM   #20
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Adding R-22 increases suction temperature???


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Originally Posted by psehorne View Post
Here are my measurements with the outside temp now 89F:
Air temperature entering the evaporator (dry bulb) ~74F.
Wet-bulb arrived at by calculating from above and RH 38% = 74F.
Outdoor air temperature entering condenser (dry-bulb) 89F

According to the chart on the unit the above results in a superheat requirement of 27F
When I entered the barometric pressure into the wet-bulb calculator I entered 3002 instead of 30.02. The correct wet-bulb is 59F, not 74F. So, the superheat requirement is still off the chart. Darn!

What's a guy to do???
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Old 07-28-2012, 11:44 PM   #21
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Adding R-22 increases suction temperature???


Using the formula I provided it should be 4 degrees.
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Old 07-28-2012, 11:49 PM   #22
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Adding R-22 increases suction temperature???


Once you get it to 4 degrees (with your 59 wet bulb and 89 ambient) take the air temperature at the nearest supply grill to the unit and then the temperature at the return air grill. Let us know the difference between these two temps.

Do not use a laser temperature gun if you have one. Use a thermometer, even one for cooking if you have one.
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Old 07-29-2012, 12:02 AM   #23
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Adding R-22 increases suction temperature???


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Originally Posted by Doc Holliday View Post
Once you get it to 4 degrees (with your 59 wet bulb and 89 ambient) take the air temperature at the nearest supply grill to the unit and then the temperature at the return air grill. Let us know the difference between these two temps.

Do not use a laser temperature gun if you have one. Use a thermometer, even one for cooking if you have one.
Ah! I forgot about your formula.

I added some refrigerant before I discovered my barometric pressure / wet-bulb error.

Current measurements
  • Supply vent temperature 55F. Return air 74F. = 19F diff. (Fluke digital thermocouple thermometer).
  • Suction gauge now 70psi/42F. Suction line temp 49. = 7F superheat
  • High pressure now up to 290psi.

Paul
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Old 07-29-2012, 12:03 AM   #24
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Adding R-22 increases suction temperature???


With a 59 wet bulb and 89 ambient 4 degrees superheat seems to fit perfectly into that chart, where 4 degrees would be if it were on there.
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Old 07-29-2012, 12:07 AM   #25
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Adding R-22 increases suction temperature???


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With a 59 wet bulb and 89 ambient 4 degrees superheat seems to fit perfectly into that chart, where 4 degrees would be if it were on there.
Yep. I will have to make a point to remember your formula.

So I'm at 7F superheat now. Too much? Do I need to remove some R-22?

Thanks,
Paul
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Old 07-29-2012, 12:08 AM   #26
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Adding R-22 increases suction temperature???


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Yep. I will have to make a point to remember your formula.

So I'm at 7F superheat now. Too much? Do I need to remove some R-22?

Thanks,
Paul
And what about the high pressure at 290psi? Too much?
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Old 07-29-2012, 12:14 AM   #27
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by psehorne View Post
Ah! I forgot about your formula.

I added some refrigerant before I discovered my barometric pressure / wet-bulb error.

Current measurements
  • Supply vent temperature 55F. Return air 74F. = 19F diff. (Fluke digital thermocouple thermometer).
  • Suction gauge now 70psi/42F. Suction line temp 49. = 7F superheat
  • High pressure now up to 290psi.

Paul

I'd add a bit to get to 4 degrees. I'm not sure why your head pressure is so high but I don't like the low saturation temp, too close for comfort.

Is your outside unit clean? Can you take a hose to it while it's running? First add a little bit of refrigerant getting it to 4 degrees of superheat and let the system stabilize there for a few minutes. Then run some water all over the heat pump coils as the unit is running, the sides, and watch your head pressure. It should lower substantially. Then watch it climb back up as the unit dries up. Then see where the pressures come to rest at once the unit is completely dry.

After it's dry take the superheat calculation again, where it's actually at (is it still at 4?) and where it should be as the outside temperature may have cooled down a bit.
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Old 07-29-2012, 12:15 AM   #28
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by psehorne View Post
Yep. I will have to make a point to remember your formula.

So I'm at 7F superheat now. Too much? Do I need to remove some R-22?

Thanks,
Paul
Adding refrigerant decreases superheat. Add some to bring it down to 4.
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Old 07-29-2012, 12:26 AM   #29
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Adding R-22 increases suction temperature???


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Adding refrigerant decreases superheat. Add some to bring it down to 4.

You just cleared up one of my misconceptions mentioned in my original post. Your statement is consistent with the statement on Payen's charging procedure. "Add refrigerant to lower suction line temperature." (decreasing superheat).

I'll add some more R-22 and hose down the unit. Will report back.

It's after midnight here in Texas. I don't know what timezone you are in, but in any event I appreciate you staying up with me. You may not hear from me again tonight. But tomorrow I will update you. Thanks for all your help.

Paul
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Old 07-29-2012, 12:27 AM   #30
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Adding R-22 increases suction temperature???


pse, I gotta go to sleep, work early in the morning. Try the water trick to bring down the head pressure. A high head pressure is a sign of a clogged condenser coil, may need to be taken apart and chemically cleaned.

Good luck. I'll check back in after work tomorrow.

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