dirty condenser coil, pressure+temp

[TheDuke]

split air cooled comfortmaker 3 ton
suction pressure 80
head pressure high side 215

suction line temp. 62f
high line temp 95f

outside air temp going into condenser 76f

note long line set evaporater and blower in attick above second foor used for second floor only.

customers complaint not cooling good

took air temp out of upstairs register 63f

took air temp going back in return upstairs 73f

[mo-flo]

overcharge?..

[hvac-tech-lane]

suction pressure 80=48 degree f,suction line temp. 62f=14 degree f superheat
high line temp 95 degree f, head pressure high side 215=107 degree f=12degree subcooling
Not overcharged
107 degree saturated condensing temp.outside air temp going into condenser 76f=31 degree f delta t
High for newer (10 seer) about normal for older equiptment
coil probabaly needs cleaned, charge may be a little low.
10 degree f delta t at registers? need to check at air handler you may have a loose/leaky return system.

note long line set evaporater and blower in attick above second foor used for second floor only.

liquid line my be under sized and flashing in hot attic , may need to be up sized and/or insulated.

Last thoughts: you probably have a combination of problems here that have accumulated to cause a loss of performance the last thing could be a weak compressor, the key as always is to look at the complete system.
Let us know what you find out.

[mo-flo]

yeah dump the juice to it and see where your superheat goes....i would think overcharge or low airflow is what i would be looking for...i would want my superheat a little more than what you got now...

[bb]

For an older system pressures would be ok.

I was thinking leaky return also. Take temp measurements at return inlet at air handler and return grille to exclude return leaks.

[davidr]

Originally posted by hvac-tech-lane
suction pressure 80=48 degree f,suction line temp. 62f=14 degree f superheat
high line temp 95 degree f, head pressure high side 215=107 degree f=12degree subcooling
Not overcharged

10 degree f delta t at registers? need to check at air handler you may have a loose/leaky return system.

I think lane may be on to your problem here.
Your problem may not be with the equipment just the ductwork it is attached to.
The duct system may not have adequate insulation & you may be gaining heat through it from the attic.
The other culprit as lane mentioned is duct leakage.
Take some temperature measurements at the equipment to see how much gain you are getting through the ductwork.
Try this formula when you take those measurements:

supply temperature at the farthest grille minus supply temperature at the evaporator divided by the delta T through the equipment= the % of BTU gain through the ductwork.
Example:
temp at farthest grille- 63 degrees
temp at evaporator- 53 degrees
delta T at equipment- 20 degrees

63-53 = 10 degrees divided by 20 degrees= 50% loss in capacity through the ductwork.
Not saying this is your problem but it will give you somewhere to look.
Try checking the static pressure & verifying you have proper airflow across the evaporator in addition to this.

Good Luck

[mo-flo]

leaky return it could be....80SP would be high pressure for 73 indoor...

[hvac-tech-lane]

Originally posted by mo-flo
yeah dump the juice to it and see where your superheat goes....i would think overcharge or low airflow is what i would be looking for...i would want my superheat a little more than what you got now...

With respect sir at only 12 degrees subcooling how would you suspect overcharge? And at 10 degree delta across evap with 80 psi suction and 14 degrees superheat how would you figure low air flow?

[hvac-tech-lane]

Duke, what type of metering device? also how much diference in elevation is there between where you are taking your readings and the metering device, this will affect your subcooling thus if you have a solid column of liquid at the metering device.

[Edited by hvac-tech-lane on 06-18-2005 at 05:03 PM]

[beenthere]

Sure sounds like its sucking attic air, with that 80 psi suction pressure.

[TheDuke]

THE METERING DEVICE IS A CAP TUBE
the line set up around 25 feet to the attic another 17 feet to the evap total 40feet
also has electronic air cleaner pulled it look clean

Now when u walk in the front door stairs are on the left open ceiling is like 25 feet high with skylights in that part of the house.
One big room in front of the house, at the top of the stairs there is like 28 feet of railing u can look down from up there are 4 rooms up there.

also three registers off that balcony and two small returns
They had the bedroom door closed to the master bedroom with the t-stat took temp off that return and register also ones off the balcony.
note bedroom was cool

I thought maybe the air coditioning for the down stairs may not be cooling enough and maybe upstairs was working harder for that.
so I took reading off down stairs unit too.
used to cool down stairs
suction pressere 65
head pressure high side 185
outside temp air ging in condenser 76f
suction line temp 59f
high line temp 92f
small refrigerant under charge
also registers down stairs 61f
return grill 74f
did not check out blower downstairs homeowner said they had a electronic air cleaner there also they clean once a year told em to do it every six months.
anyway i was on this service call for the upstairs unit just thought i would go the etra mile.
there initail complaint upstairs not cooling
cold it be the dirty condenser for up stairs and the little bit of the low charge down stairs unit be the problem.
well will take all opinions thank you

[TheDuke]

oh Duct work is all good went all through attick.
no leaks tight best i seen in a while

[beenthere]

40' isn't that long.

First clean the condenser coil.

Then run it again, and when the system stabilizes recheck the readings.

If you still have the same basic readings, then shut the indoor fan down and watch the frost lines.
You could have a slight restriction in one of the caps, and someone else may have added gas last year or earlier to get it to cool again.