Tempstar Ultra High Efficiency Servicing

[jdob28]

Furnace: NTG3075FBA2 - Evaporator coil: EXD42J22A1 - Compressor Unit: CA9630VKB2.

I had this system installed when our house was built in 1998.  About 1500sqft of cooling space.  Ever since it was installed it never cooled very well.  I had service men out yearly for the first 5 years and they all said it was doing the best it can.  I did change the fan speed to "high" because the installer left it on the default tap that did not have the CFM flow that is required by this evaporator coil.  This helped a little, but not much.  I finally had enough this year and  had a friend of mine who recently got his EPA certification and has the gauges etc. to come over.  Before we serviced my system the house was 82F. running continually.  The thermostat was set at 78F.  Outside temp was 92F.  The low side was running at 66psi and the high side was 189psi and the superheat was over 57F!  Long story short, to get the superheat down to 19F it took a low side pressure of 86psi and high side of 210psi.  Does this seem reasonable?  Should I keep servicing it until the superheat is less than 10 or 15F as long as the low side stays below 90psi? It seems all the servicemen didn't understand superheat and where afraid to raise the low side above 70 or 75psi.  Now my house actually stays at 78F. at 93F outside!  First time in 8 years.  Why didn't the servicemen understand my system?  I am writing this because it  really makes me mad as hell that it took my research on the internet to correct the problem and not the 5 different "certified serviceman" that I paid $$ to do absolutely nothing!  I am starting to rant, sorry. Anyway, any thoughts on the subject are appreciated.

[Guest ahammer48]

Hello

It is sad but true that most service ppl of home ac units don't bother checking things like superheat, sub cooling etc. The mentallity seems to b (its a small system, how much could go wrong) and it takes to much time. I've got 7 other other service calls to hit before I can go home.

I think your system is still short refrigerant. Rule of thumb for super heat is U want 8-12 degrees of it.

If Ur friend has a T/P chart(temperature/pressure) do this. I'm assuming Ur machine uses R-22. Measure the OAT(outside air temperature) and add 30 degrees to it.

In UR post U had an OAT of 92 degrees. Add 30 and U get 122. On my T/P chart 4 R-22 that would give U a head pressure of apprx 265 PSIG. So on that day UR head pressure should have been that.

Yes U will run a high suction pressure. Thas because its hot outside and UR house is hot. As the temp in UR house comes down so should UR suction pressure.

Continue to charge the unit untill U get close to the head pressure U should be running at 4 the OAT u have at that time.

Hope this helps:)

[jdob28]

Thanks for the advice.  I got the phone number for a TempStar TSA in my area and he said because my system has an expansion valve, I need to service using "subcool".  He said the subcool temp should be listed on the data tag on my unit.  All I see is "final serviceing done using installation guide or tech sheet" or something like that.  I looked through all the data sheets that came with the unit and all I see is service instructions for an "variator and piston"  type evaporator, not one with an expansion valve.  How much subcool should I have?  Or should I just go for the OT + 30 = low side pressure?  Thanks

[Brew Man]

Hey,

First off,you need 12,000 btu for every 400 sq ft.or one ton for every 400 sq foot of space to be cooled.So your house is 1500,you need a unit that has a cooling capacity of at least 4 ton or 48,000 btu's.As for thr ot+30,that has to do with your outside condenser or high side.

[jdob28]

I finally got an answer from Tempstar.  My condensor unit is designed to run at 10 deg. subcooling.  I rechecked the servicing and it is running at exactly that.  I can actually use the oven and the AC can keep up.  That never happened before!  It was 94 deg. outside yesterday and the house stayed at 78 deg.  High side ended up at about 214 psi.  Thanks for the info everyone.

[Rrey199]

:shock: Old rule of thumb (1cfm/sq.ft.) sometimes works, but with newer construction, is way off. With insulations reaching R49 in the attic and R39 in the walls, it ends up being more like .75 or even .5 cfm/sqft.

The only right way to size is with maual J.

[Brew Man]

Hey,

I've been in the newer homes and alot of the rooms built over the garage aren't even isulated,They say it's not required by code.You try to go by 500 sq ft per ton and you will be like alot of people in phoenix,arizona.Very unhappy with the cooling their ac provides.