proper subcooling readings

[stvokc]

New installed complete 5 ton system with TXV. The discharge thermostat is shutting condenser off after about 2.5 - 3 hours of run time. Then after about 2 hours the condenser runs again (discharge thermostat resets itself).

I checked customers subcooling, it is 18. I am thinking system is over charged. System is a 12 Seer Armstrong.

If I have this right I need to lower subcooling to around 12-15 by letting out some freon. I do not know what the subcooling should be for sure on an Armstrong unit. Can someone inform me what it is for an Armstrong 12 Seer?

The 18 subcooling is making the compressor run harder and causing higher discharge pressure which causes higher discharge temperature. Thus causing the discharge thermostat to over heat and shuts the condensor off.

Do I have this right?

[crzshn]

so you took some freon out ....and all was okay?

[stvokc]

No I have not taken any freon out yet as I wanted to be sure I have this correct and the proper subcooling reading I should come to when I take some out. House is empty so will not bother anybody if condesor shuts off for 1 1/2 hours.

[RoBoTeq]

I don't like to see 18º subcooling. Too much liquid is stacking up in the condenser. I would adjust the subcooling to 12-15º, then check to be certain the TXV is providing the proper superheat.

[bornriding]

If 18 subcooling, then vapor is turning to liquid inside the outdoor coil, removing refrigerant would cause a higher subcooling no. as less vapor in the outdoor unit will cause less time to condense, causing the saturation point to move further inside condenser.
the question is what is causing the temp to rise enough to open the thermostat.

[resolutetech]

removing r22 would lower subcooling and head pressures if the system is over charged and not restricted. removing the excess liquid in condenser gives the gas more space to give off heat and become a liquid which is good.

[stvokc]

Everything in the system is new and it is R22.

Last 2 responses said to do opposite things (one said ad freon the other said to remove freon).

Sysytem has sight glass and it is clear and dry.

[stvokc]

gauge reading were 70 low side and 142 high side. Outdoor air tempature around 90.

[RoBoTeq]

resolutetech is correct, I'm not sure that bornriding has proofread his post :D

Pressures alone tell us absolutely nothing other then a very basic range of info (OK, if the head is 300 and the suction is 20, there is a problem).

You mentioned subcooling; what are you calling subcooling?

142 head seems low for a 90º day, but could be with some higher efficiency systems.

[snewman24]

Originally posted by RoBoTeq
142 head seems low for a 90º day, but could be with some higher efficiency systems. [/B]

Sounds impossible to me. 142 PSI corresponds to about 79°F.SCT which is 11°F. BELOW outside ambient air temp. of 90°F.

[stvokc]

I was giving you pressures off the r22 scale.

On PSI scale pressure would be 70 low side and 210 high side with pressure temp of 106 and line thermostat temp was 88.

[smokin68]

Subcooling should be around 12-15, but you need to measure your superheat to see what's happening in the system. those pressures seem low for 90 degrees, but without more readings it a guess. SH/SC,ambient, delta t,ect.

[RoBoTeq]

Originally posted by stvokc
I was giving you pressures off the r22 scale.

On PSI scale pressure would be 70 low side and 210 high side with pressure temp of 106 and line thermostat temp was 88.

I for one have no idea what any of this is supposed to mean. Are you in the HVAC business?

[snewman24]

Originally posted by stvokc
I was giving you pressures off the r22 scale.


The green R-22 scale is showing Saturated Temp. - not PSI

It would also be helpful to know what amperage the compressor is drawing, along with the other parameters the others have mentioned.

[airworx]

no. higher subcooling values means lower condensing tempertures. the highest subcooling factor i have seen on a residential system is 18. i would call your distributor or armstrong to find proper subcooling. it is usually listed on the name plate. but i charge till system operates around 20 degree superheat at probalby 10 to 12 degrees subcooling.
as far as the discharge stat it may be faulty or your superheat is real high.