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Old 07-28-2012, 09:04 PM   #1
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Adding R-22 increases suction temperature???


I am trying to understand what I am seeing on my gauges. (I have an HVAC Certification, but have never earned a living professionally in the HVAC industry).

The unit in question is a Payne Heat Pump PH10JA030. The instructions I have say that if the suction temperature is not at target adding refrigerant will lower the suction temperature and removing refrigerant will increase the temperature. I am seeing just the opposite. Can any of you shed some light on this?

Here are my measurements:
Air temperature entering the evaporator (dry bulb) ~73F.
Wet-bulb arrived at by calculating from above and RH 45% = 62F.
Outdoor air temperature entering condenser (dry-bulb) 105F

According to the chart on the unit the above results in a superheat requirement that is off the chart to the low side. In other words, less than 5. Because of this I am concerned that the unit may be overcharged.

Other pertinent measurements:
High pressure line gauge reading PSI/temp = 270psi/122F
High pressure line actual temperature = 113F (subcooling ~9f)
Suction line gauge reading PSI/temp = 70psi/41F
Suction line actual temerature = 47F
Air exiting indoor vents = 55F
Cold air return = 73 (diff = 19F)

Thanks in advance for any help any of you can offer.


Paul

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Old 07-28-2012, 09:23 PM   #2
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Adding R-22 increases suction temperature???


is your condenser coil clean? your high side pressure looks high. your super heat is a 6 degrees if I am reading your numbers correctly which at first glance seems lower than normal. I would think more like 10. What kind of metering device do you have(txv or piston)? Are you having any prefromace problems or are you just checking the unit. If I was not an experianced tech I would not make any changes to a working unit. Try to clean the out side coil and recheck the system.

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Old 07-28-2012, 09:25 PM   #3
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Adding R-22 increases suction temperature???


Both high and low pressures will increase as refrigerant is added and decrease when removed.

Here's a good formula for target superheat. Btw, superheat for fixed orifice/piston metering device and subcool for thermostatic expansion valves.

3 x's the wet bulb
- 80
- ambient temperature (outside temperature)

divided by 2 = what your superheat (piston) should be.

You can search "calculating superheat" on Youtube as well as find that formula all over the web if you want to confirm it.
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Old 07-28-2012, 09:27 PM   #4
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Adding R-22 increases suction temperature???


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Originally Posted by turnermech View Post
is your condenser coil clean? your high side pressure looks high. your super heat is a 6 degrees if I am reading your numbers correctly which at first glance seems lower than normal. I would think more like 10. What kind of metering device do you have(txv or piston)? Are you having any prefromace problems or are you just checking the unit. If I was not an experianced tech I would not make any changes to a working unit. Try to clean the out side coil and recheck the system.
We all help each other out around here, tech to tech. Ask beenthere how much I bug him!
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Old 07-28-2012, 09:44 PM   #5
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Adding R-22 increases suction temperature???


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Originally Posted by turnermech View Post
is your condenser coil clean? your high side pressure looks high. your super heat is a 6 degrees if I am reading your numbers correctly which at first glance seems lower than normal. I would think more like 10. What kind of metering device do you have(txv or piston)? Are you having any pereformance problems or are you just checking the unit. If I was not an experienced tech I would not make any changes to a working unit. Try to clean the out side coil and recheck the system.
Turnermech,
Thanks for your reply. Your questions answered below.

The condenser is relatively clean (it was hosed off a few weeks ago), but could be cleaner. I will clean it tomorrow.

I am not sure about the metering device. However, I think it has a piston in cooling mode and TXV in heating mode. The label on the machine gives superheat instructions for cooling mode and subcooling instructions for heat mode. (Is that a clue?).

I had a problem a couple of days ago. Turned out to be very dirty air filter, but in the process of troubleshooing I checked the pressures and temperatures. At the time I did not know it, but I had a defective low pressure hose on my gauges/manifold. It appeared to need refrigerant; so I added some. Reading were not normal; that is when I discovered the bad hose. I received a new gauge/hose/manifold set yesterday (my old set was ~30 years old). So the measurements I posted here were done with my new gauges/hoses/manifold.

Regarding the 6 degrees superheat. It does 'seem' low, but, again, the chart on the instrument shows that with my outside temp of 105F and air entering evaporator at 62F wet-bulb, the required superheat is even less than 6. The required superheat is off the chart scale below the 5 minimum shown.
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Old 07-28-2012, 09:44 PM   #6
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by Doc Holliday View Post
Both high and low pressures will increase as refrigerant is added and decrease when removed.

Here's a good formula for target superheat. Btw, superheat for fixed orifice/piston metering device and subcool for thermostatic expansion valves.

3 x's the wet bulb
- 80
- ambient temperature (outside temperature)

divided by 2 = what your superheat (piston) should be.

You can search "calculating superheat" on Youtube as well as find that formula all over the web if you want to confirm it.
Doc,
Thanks for your reply.

I am not seeing any significant change in pressures when adding or removing (a small amount of) refrigerant. They are pretty stable at 70 and 270.

But I am seeing the temperature of the suction line increase when adding refrigerant and the temperature of the high side decrease when adding refrigerant. Can you comment on this scenario?

And thanks for the formula, but I am using the manufacturer's chart. I will recalculate the superheat requirement using your formula and compare that with Payne's chart.

Thanks,
Paul
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Old 07-28-2012, 09:52 PM   #7
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by Doc Holliday View Post
Here's a good formula for target superheat.

3 x's the wet bulb
- 80
- ambient temperature (outside temperature)

divided by 2 = what your superheat (piston) should be.
Doc, using your formula I come up with:

[(3 x 62) - 80 - 105] /2 = .5

Hmnnn.... Please comment.

Paul
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Old 07-28-2012, 09:57 PM   #8
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Adding R-22 increases suction temperature???


your temp is increasing when adding refrigerant because you are affecting the pressure temp relationship. 70 psi = around 40 degrees 80= around 50. did not look it up just off top of my head might be a little off. It seems as if you have a txv by what you are describing as your suctions is staying at 70 while I guess you head press is climing. the door of your unit may have a chart for super heat and yes that would be for piston. but this could also been matched with a txv unit when installed. A txv will try to maintain the 70 psi and 40 temp to an extent when overcharging. A piston would not. Super heat is also not bad to check when charging a txv but changes can't be made based on superheat. A txv will adjust to attempt to maintain the super heat. you have to use subcooling. If you have the refrigerant to spare try to remove untill you see the low pressure just start to begain to fall below 70. observe you high side pressure and see if it falls back to a more normal pressure. retake all of your readings.
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Old 07-28-2012, 09:59 PM   #9
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Adding R-22 increases suction temperature???


Pic attached of the Payne superheat-required chart. Notice that 62F wet-bulb and 105 outdoor temp is off the chart.
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Adding R-22 increases suction temperature???-payne-superheat-required.jpg  
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Old 07-28-2012, 10:05 PM   #10
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Adding R-22 increases suction temperature???


take the refrigerant out slowly. Allow it to bleed from your liq line through you red hose with the manifold valve into a reclaim cylinder. let it out in small burst allow several min to pass( some times takes as much as 10 min for a change to take place)while checking your pressures and temps between burst. as expensive as r-22 is I dont want you to waste it.
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Old 07-28-2012, 10:06 PM   #11
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Adding R-22 increases suction temperature???


Half a degree superheat would be way too low, even if the formula says it's correct. It would only take another one half of a degree for the vapor to change to liquid and that is the main concern when it comes to superheat and subcooling, making sure the refrigerant stays in it's designated state either to the evaporator or on it's way back from the evaporator to the compressor. It just so happens that we can also determine system charge this way.

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.

Too little superheat most likely does mean overcharged. What's happening is the system has too much refrigerant, might even still be some liquid on the way out which is not good. Liquid returning to the compressor will eventually kill the compressor. In this scenario liquid is most likely making it way past the piston and cap tubes, all the way into the evaporator. Saturation is most likely not occurring until a third or halfway into the evap and again, floodback would be a serious concern.

Is this an old system or a new one or what? Piston or txv?
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Old 07-28-2012, 10:07 PM   #12
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by psehorne View Post
Pic attached of the Payne superheat-required chart. Notice that 62F wet-bulb and 105 outdoor temp is off the chart.
if its off the chart it means you cant use the chart. you have to change the inside condition to be able to use the chart.
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Old 07-28-2012, 10:09 PM   #13
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Adding R-22 increases suction temperature???


Quote:
Originally Posted by psehorne View Post
Pic attached of the Payne superheat-required chart. Notice that 62F wet-bulb and 105 outdoor temp is off the chart.
That's because they design them at a nominal operating temperature. What you have is an extreme temperature. Again, go back when it's cooler outside and check it. It'll make sense then.
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Old 07-28-2012, 10:31 PM   #14
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Adding R-22 increases suction temperature???


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Originally Posted by Doc Holliday View Post
Is this an old system or a new one or what? Piston or txv?
Unit was installed new in November 2002. It has never caused a problem. The reason I got to checking it is because it quit working a couple of days ago - my fault... filter was very dirty. Unit has not caused a problem, but now that I changed the charge (see previous post where I reported that a defective hose caused me to add refrigerant) I'm concerned that it might be overcharged.

Rereading the manual I have[on PH10xx-048 (4 ton) and 060 (5 ton)] . It shows metering devices inside and outside as piston. I would assume that is also the case for the -030 (2.5 ton).
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Old 07-28-2012, 10:32 PM   #15
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Adding R-22 increases suction temperature???


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Originally Posted by turnermech View Post
take the refrigerant out slowly. Allow it to bleed from your liq line through you red hose with the manifold valve into a reclaim cylinder. let it out in small burst allow several min to pass( some times takes as much as 10 min for a change to take place)while checking your pressures and temps between burst. as expensive as r-22 is I dont want you to waste it.
Will take a look at doing this tomorrow.

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