Not cooling

[DNMechanical]

I'm working on a 3 ton Trane ac system....bout 12 yrs old...
The house is not cooling properly.
83 degree outdoor
Low side 74 psi, 1.9 super heat.
Hi side 178 Psi, 3 subcool
18 temp drop across the coil... 81 return - 63 supply.
I couldn't figure out what's wrong with it

[njaircond]

you want to check the square feet of the house it's look like you compressor is a week your low side should be about 60 65 PSI
make sure your square feet is the same as the regional NO extension added also I'm not sure where the system if it's an attic make sure you don't have any doubt leaks including the return
http://www.liebertairconditioning.com

[jpsmith1cm]

Wet bulb temps would help.

As would airflow.


I do not suspect your compressor, but I do suspect multiple problems here.

Low airflow and low charge most likely.

[AStudent]

I'm working on a 3 ton Trane ac system....bout 12 yrs old...
The house is not cooling properly.
83 degree outdoor
Low side 74 psi, 1.9 super heat.
Hi side 178 Psi, 3 subcool
18 temp drop across the coil... 81 return - 63 supply.
I couldn't figure out what's wrong with it

1.9 is a bit low for super heat.

Does the unit have a TXV or fixed orifice?

What type of refrigerant is in the unit?

I'm thinking it's overcharged but we need more information on the unit.

[DNMechanical]

r-22. fix orifice. I pretty sure it had multiple problems but just couldn't figure it out ..unit is in attic.. no no air leak....

[jpsmith1cm]

1.9 is a bit low for super heat.

Does the unit have a TXV or fixed orifice?

What type of refrigerant is in the unit?

I'm thinking it's overcharged but we need more information on the unit.

Subcooling indicates a low charge.

Low superheat tends to point towards a low airflow, particularly since the subcooling is low as well.

:cheers:

[AStudent]

High side pressure too high...low side is spot on..with a fixed orifice. What does this indicate?

[jpsmith1cm]

r-22. fix orifice. I pretty sure it had multiple problems but just couldn't figure it out ..unit is in attic.. no no air leak....

Not thinking about an air leak, I'm thinking that you don't have enough air moving across the evaporator coil.

[DNMechanical]

if not enough air move across evap, it will cost low suction presure

[DNMechanical]

@ASTUDENT.... high side is too low (NOT HIGH). low side is about right...

[jpsmith1cm]

High side pressure too high...low side is spot on..with a fixed orifice. What does this indicate?

Pressures alone are largely meaningless.

[jpsmith1cm]

if not enough air move across evap, it will cost low suction presure

It will cause low Superheat, first,

Your 81 degree return temp would help to keep that suction pressure up.


Did you measure the airflow?

[jpsmith1cm]

@ASTUDENT.... high side is too low (NOT HIGH). low side is about right...

Low high side pressure would be consistent with low load caused by low airflow.

:cheers:

[J/D]

High side pressure too high...low side is spot on..with a fixed orifice. What does this indicate?

R-22 system with 83* outdoor temperature 178# head pressure seems low not high would expect 200# very little subcooling would agree with JP low charge and not enough airflow across the evaporator causing the low superheat.

[DNMechanical]

i'm suspecting not enough airflow at one point...I wish i have airlfow meter...

[DNMechanical]

i checked motor, it seem running fine, normal amp draw, coil clean...

[jpsmith1cm]

i'm suspecting not enough airflow at one point...I wish i have airlfow meter...

A manometer would be a good investment.

Without measuring airflow, you cannot make good diagnoses on problems like this.

[DNMechanical]

before all this happens,, evap coil had a leak. I fixed the leak. purge nitrogen during brazing. pulled vaccum to about 750 micron...

[DNMechanical]

@jpsmith1cm. agree with you. i'm gonna invest on a manometer

[Tech it out]

Just checking in cause I want to see how it turns out. :pop:

[54regcab]

18 degrees across the coil should get the house cool unless you have poor airflow.

[timebuilder]

18 degrees across the coil should get the house cool unless you have poor airflow.



...and if you have that 18 degrees WHILE you have low airflow, then what happens to that split when the airflow is corrected? 10? 8?

Fix the airflow and then knock down these ducks, one at a time.

[VTP99]

I say gas that thing up already and stop playing around. At 83* ambient pressure should be over 200#. Unless the coil was a block of ice. :rolleyes:

[AStudent]

Thanks guys...looks like I would have really messed this one up.

[Tjune54]

Check the FCCv and make sure it is seated in the housing. If not fully seated it will bypass liquid into the evap and cause the conditions you describe.
I have found this more in The Trane heat pumps but have found a few in just a/c as well.

[DNMechanical]

what is FCCV?

[AStudent]

A FCCV is the metering device on older Trane units, if not seated right it could like Tjune54 said allow too much refrigerant into the coil.

[DNMechanical]

I will take a look at the FCCV, b/c I did take that FCCV out when I fixed the leek. I hope that is the problem...I will let ya know if it solve the problem or not .



Check the FCCv and make sure it is seated in the housing. If not fully seated it will bypass liquid into the evap and cause the conditions you describe.
I have found this more in The Trane heat pumps but have found a few in just a/c as well.

[hvacrmedic]

I'm working on a 3 ton Trane ac system....bout 12 yrs old...
The house is not cooling properly.
83 degree outdoor
Low side 74 psi, 1.9 super heat.
Hi side 178 Psi, 3 subcool
18 temp drop across the coil... 81 return - 63 supply.
I couldn't figure out what's wrong with it

I'm going to speculate that your compressor is under-pumping and the indoor airflow is very low. I wouldn't rule out over-metering though, which will produce similar symptoms to an under-pumping compressor. I would expect the superheat to be exactly 0° in that case though. Measurement error maybe?

[54regcab]

...and if you have that 18 degrees WHILE you have low airflow, then what happens to that split when the airflow is corrected? 10? 8?

Fix the airflow and then knock down these ducks, one at a time.

Good point.

[DNMechanical]

just want to give y'all follow up. I came back to the house and took the FCCV out and put it back. I made sure it seated in there correct... here are the result before and after.
Homeowner was in the rush to going to church, so I did it really quick without noting all of the info, but here are the most important info
outdoor 67degree, indoor 75 8:00 AM

before after
18 temp split
Low side = 69 psi Low side was around 20 PSI
hi side = 165 psi hi side was around 160
1-2 SH 50 SH
3-4 SC forgot about SC

I figured it was low on charge. I charged it up accordingly. got 20 temp split. house cooling good. Since it not hot outside, so i'm gonna call him back whenever outside temp gets hotter. But I think I solved the problem. Many thanks to you guys...







Check the FCCv and make sure it is seated in the housing. If not fully seated it will bypass liquid into the evap and cause the conditions you describe.
I have found this more in The Trane heat pumps but have found a few in just a/c as well.