# I am stumped Read this..!



## Dapster1

As a part time Service Tech (I am semi retired) for a small company I have run accross this problem and have recieved 2 callbacks on this problem.
Customer Complaint:
Air cools good but runs far too often when temps get above 90. Stat set at 75 and it will reach set pt. ( has 40-50 min run times during the day) Has Honeywell digital stat

I responded to this call today at 2pm and here are my findings:
Goodman 3 ton 12 seer straight cool Fixed piston-R22 with gas furnace.

Suction pressure/71 head/248
Sh ~11-12 Sat temp 54 
Oat 93
IWB 64.2
Supply 57
Return 78

On the first call I did a complete service -cleaned coil, replaced filter and adjusted charge..(This customer had about a 17 Sh with near same conditions)
I am concerned on the return temp and the humidity level. Any suggestions please chime in...Fan speed? settings are factory set. This unit is only 4 yrs old too. What can I do to optimize this system. Anyone want to chime in please post..Robo/Beenthere
Thanks!


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## beenthere

With the return temp and WB you posted, you only have a 47%RH, pretty good. Is 78 what the thermostat is set for? 40 to 50 minutes isn't really a long run time for a 93 degree outdoor temp. 

Sounds like the system is sized pretty close to what the house needs. Are they also complaining that the electric bill is also high? Or do they just think its not good for the A/C?


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## Dapster1

Thanks for responding...I am beginning to think that all is ok too but the Home Owner thinks that it runs too long when tstat is set at 75 and oat is 93-94
78 was the temp taken at the return where the air handler is mounted vertically in the Garage and a 56-57 supply so I thought the delta t was not range for a 18-20 target as I am used too.
I told her that I will be there on Tues to check on the system further.


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## beenthere

When its 98 outside and I'm maintaining 72 inside. my system runs for 6 hours at a time. Shuts of for 10 minutes and then runs for another 5 hours or so. I smile because my humidity is low, and I am comfortable. if it ran for shorter periods of time, my humidity would be high, and I wouldn't be comfortable.

Their system is operating fine. bet if they go to a neighbors house where it only runs for 20 minutes when its 93 outside and 75 inside, they would be uncomfortable because of a higher humidity level.

Remind them, that an A/c is suppose to have long run times as it gets hotter out. And at some point it should run non stop for hours.


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## Dapster1

Thanks Beenthere
The customer did mention that it has run even longer 60-90 mins at a time with stat set at 75. As a test mine ran 55 mins today and I was showing 97oat in my backyard! I have been contemplating changing the piston to a TXV for this customer but feel like all is really ok. I also forgot to mention that after my original service and coil cleaning, It dropped the current on my Compressor by almost 1 amp. I will post additional comments on Tues after I go to this home......Thanks again.


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## beenthere

A TXV won't really change how long the system runs.


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## chrisfrost

Wow , You guys out to try a Phoenix HOT day ,,,,,,,,,115 and most everyone has an oversized unit because nobody wants to risk not being cool enough on hot days so even at 115 a good working unit will only run about 20 - 25 min / hour ,,,,,,,,maybe 30min/hour max , but humidity is'nt a huge problem here ,,,,,20-30% on average .


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## NRG$WIZ

How large of an area are you trying to cool/supply temp should be colder/any liquid line filters/coil was cleaned cond or evap/solar gain/
locatian of t-stat/air flow /filters location -found a filter in the supply
once. Good Luck


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## scooter

I did not notice this the first time through, but what do you mean by Fan speed? settings are factory set.
I guess I havent seen a furnace only four years old, that did not have some sort of adjustablitiy to the blower. 
I would think that would be fairly critical if you wanted to adjust temp rise/drop.


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## nicktech

i would do a heat load calc to see what the house need vs what it has. 6 hr run time, damn. the units are design at 95 OAT as a standard.


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## Tony Pullen

*re*

how well is the home insulated?


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## JimEmac50

*RE*

​When someone complains that it's constantly running, and after checking the system I get 17 to 20 TAC, I tell them there's nothing wrong with the system with an outside temp of 95.
I'd be looking at the CFM output in each room to determine is the ductwork is the right size.
My system at 95 plus OT only runs about 30 min. at a time tops & Humidity at 55 to 60% indoors.
Other have complain same, but no basement and all the ductwork in attic....... not gonna cool much of anything.


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## ironpit

might check the return in the attic to see if any air being pulled into the return. could be just a small leak that makes a big difference.


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## eidson

What is the length of the line set? Looks like may need just a little more 22 to it. If the LS is 40 to 50ft you will need 18 to 25 SH.


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## Saturatedpsi

eidson said:


> What is the length of the line set? Looks like may need just a little more 22 to it. If the LS is 40 to 50ft you will need 18 to 25 SH.


The OP is 6 months old...but are you saying superheat is adjusted to line-set length? :blink:


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## eidson

*yes*



Saturatedpsi said:


> The OP is 6 months old...but are you saying superheat is adjusted to line-set length? :blink:


Yea, if you have a 40 to 50 ft LS you will have to have a little more SH to it. It have to figure for it cuz your temps at the suction valve will diff. from short to long. Just as if you set a new unit you have to add 3oz to every 5ft of LS in most cases.


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## Saturatedpsi

eidson said:


> Yea, if you have a 40 to 50 ft LS you will have to have a little more SH to it. It have to figure for it cuz your temps at the suction valve will diff. from short to long. Just as if you set a new unit you have to add 3oz to every 5ft of LS in most cases.


Just in the interest of friendly debate, that's the first time I've seen line-set length considered in adjusting superheat. I can see some additional heat gain with increased length, but if the "charging chart" calls for 10 F at the service valve for a particular set of indoor and outdoor conditions, one would add freon till the 10 F was reached...or look into why there was a lot of heat gain to begin with. 

As I understand superheat, the number needs to be reasonably low to load the coil and cool the compressor, and reasonably high to protect the compressor from returning liquid. I guess it depends on what you call "reasonable". :laughing:


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## beenthere

A 50 foot line set has little to no effect on the SH reading you should have. Unless the condese is above the evap by more then 20 foot.


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## COLD 1

95/5 rule for st. cools...if its 90 Deg. or higher outside, Your superheat should only be about 5 Deg.


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## beenthere

COLD 1 said:


> 95/5 rule for st. cools...if its 90 Deg. or higher outside, Your superheat should only be about 5 Deg.


That would be on a home that is at human comfort temp already. Not one that the A/C was just repaired, and the home is hot and has high humidity.


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## rsmith46

Try using this formula for fixed metering systems to find the target superheat.
WB x 3 - 80 - odt divided by 2
So 64 x 3 = 192 - 80 = 112 - 93 = 19 / 2 = 9.5deg superheat


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## rdjr1964

How old is the system? I found a while back that the coating that was used on the condenser coil (which worked great for a while) deteriorated and caused a extremely hot liquid line which causes a lower super heat ,flooding the evap coil and thus not evaporating and absorbing the heat and removing humidity therefore the indoor comfort was unsatisfactory. They have since solved this problem.


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## acefurnacefixer

sounds like a customer that we have up north in the summer.....they are snow birds in the winter......


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## cortez

Many older customers will suddenly hear and realize that their unit is running almost non stop at 68 degrees. 

I ask if their electric bill is considerably higher, and they say no it is almost always the same in summer usage. I tell them that it is probably no concern, but a service call will be $$$ (my current rate). 

Often this is only a matter of *noticing continuous (or nearly so) running of their AC.* 

In Chicago area the summers can be brutally humid and many installers put in units that run 80 to 90 percent of the time for uniformity of cooling (this was some years ago when the "common wisdom" dictated this strategy). 

Often this could could be put to rest with with an over the phone call for the customer to report any future spike in electric cost.


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## Residentialtech

Have you checked ductwork for any leaks and attic insulation?


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