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08-01-2011, 10:23 AM   #1
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## what should the high side be?

Hey when looking at the pt chart, what do you look at to see what the high side should be?

Do you look up the outside temp and convert that? Do you look up the inside temp, sustion line temp, superheat, what?

I know how to do superheat and wet bulb all that stuff but nothing with the high side.

Thanks

08-01-2011, 10:31 AM   #2
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Superheat - Suction line
Subcooling - Liquid line

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 08-01-2011, 11:18 AM #3 Newbie   Join Date: Jan 2011 Posts: 6 Rewards Points: 10 for example say it is 90 degrees outside. suction line is say 80 PSI, webulb is 65, inside air is 75, I have not done the math but say the superheat is 20. what should the high side be and how did you get that? When I look up 90 ( for out side air) on the PT chart is converts to 168.4. way to low for high side PSI. Or is the PT chart not for high side readings? and if not how do I know what it should be? Thanks again for all the help!

 08-01-2011, 11:30 AM #4 Hvac Pro     Join Date: Nov 2008 Location: Winnipeg, Canada Posts: 16,018 Rewards Points: 174 that reading is for what the pressure in a freon bottle would be or an idle system. High pressure depends on the outdoor temp and how clean the condensor coil is. If dirty the pressure goes up. In the old days of 8 SEER units I used to add 20 deg to say 110 F and convert that to a pressure. 20-30 was norm and above that the coil was dirty or air in the system. The newer 10 SEER and over will run lower head pressure as the condensor coils are much larger so there is NO rule of thumb for pressures of any kind anymore on either side of the system. Really have to use the manufacturers subcool or superheat chart that comes with the condensor to know what to do or have more than 10 yrs experience to know what is normal. __________________ "Cut it twice and it is still too short". Last edited by yuri; 08-01-2011 at 11:32 AM.
08-01-2011, 12:08 PM   #5
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Quote:
 Originally Posted by yuri In the old days of 8 SEER units I used to add 20 deg to say 110 F and convert that to a pressure. 20-30 was norm and above that the coil was dirty or air in the system.
.

where did you get the 110 F from is that the outside temp at that time?

 08-01-2011, 12:17 PM #6 Hvac Pro     Join Date: Nov 2008 Location: Winnipeg, Canada Posts: 16,018 Rewards Points: 174 your example of 90 degF OAT plus 20-30 degF then convert to pressure from the chart. __________________ "Cut it twice and it is still too short".
08-01-2011, 02:08 PM   #7
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ok yup I got ya
Thanks for the help!

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