[mcairrepair]

Lennox LGA/LHA180 package unit

Ambient: 85°F

Condensing temp: 122°F
SC 1: 34°F
SC 2: 18°
SC 3: 25°

Evap temp: 42°F TXV metering
SH 1: 20°
SH 2: 38°
SH 3: 20°

Return: 81°
Supply: 55°
Thermostat set for 76° but manager says it never hits that.


Filters clean, belt tension good, bad economizer so outdoor air is always mixed in with the return. It's a kitchen unit for Mcdonalds so there is a lot of heat to absorb.

Any ideas on why I'm getting drastically different SH and SC but all pressures are exactly the same?

 

[ascj]

Lennox LGA/LHA180 package unit

Ambient: 85°F

Condensing temp: 122°F
SC 1: 34°F
SC 2: 18°
SC 3: 25°

Evap temp: 42°F TXV metering
SH 1: 20°
SH 2: 38°
SH 3: 20°

Return: 81°
Supply: 55°
Thermostat set for 76° but manager says it never hits that.


Filters clean, belt tension good, bad economizer so outdoor air is always mixed in with the return. It's a kitchen unit for Mcdonalds so there is a lot of heat to absorb.

Any ideas on why I'm getting drastically different SH and SC but all pressures are exactly the same?

How's that condenser coil looking?

A 26 degree td with a 81 degree return? What is your airflow? A tensioned belt and clean filters, don't mean good airflow.

 

[mcairrepair]

How's that condenser coil looking?

A 26 degree td with a 81 degree return? What is your airflow? A tensioned belt and clean filters, don't mean good airflow.

Condenser coil is clean and fins are fairly straight, good airflow. Also, airflow across evaporator is within specs.

 

[superfittertech]

26 degree split for that unit is not within specs. It should be close to 17-20 degrees If the economizer is broken, then loosen up the linkage and manually close it. It really sounds like way too much outside air. Also check your downstream dampers. ascj said it right recheck your airflow:gah:

 

[weatherpro]

You certainly need to check the air flow, and it also looks like circuts 1 and 3 may be slightly over charged.

 

[weatherpro]

also fix the economizer.

 

[superfittertech]

You certainly need to check the air flow, and it also looks like circuts 1 and 3 may be slightly over charged.

he needs to get the airflow fixed, before that can accurately be determined.

 

[mcairrepair]

So at the evaporator my airflow meter is reading 5400 cfm. When I manually close the economizer and take the reading at the return air inlet inside the restaurant I get 1400 cfm. There are two return ducts but one of them just dead ends in the attic with no air coming in. The other one doesn't seem to have any obstructions. Is that the problem? That there is only one return duct 13" in diameter?

 

[Hrdworkingacguy]

All three circuits share the same return and OSA??? The difference in SC/SH is the txv and/or the adjustment nut...All three circuits seems underfeeding to me...Possibly the outdoor coil is dirty...:eek2:

 

[mcairrepair]

All three circuits share the same return and OSA??? The difference in SC/SH is the txv and/or the adjustment nut...All three circuits seems underfeeding to me...Possibly the outdoor coil is dirty...:eek2:

Yeah it's a 3 stage package unit, everything is shared. I'm just wondering why I'm only getting 1400 cfm from the return air duct. Is that all that a 13" inside diameter duct can get? I mentioned already that the outdoor coil is clean, 1 and 3 don't seem to be underfeeding, but that's hard to tell with such poor airflow through the return air. The unit was running fine this morning when the OSA was 75° and the economizer was open all the way. It's definitely airflow. Stage 2 was still high SH in the morning, so I think there's an issue with that in addition to airflow, but we're not there yet.

 

[Hrdworkingacguy]

When you have high superheat, and high sub cooling, the liquid is in the condenser...The only thing that will cause that is liquid restriction of some kind(plugged drier, underfeeding TXV, distributor tubes clogged), or if the heat load was high and the TXV couldn't open up far enough to deal with it...

The fact that you are running a 26 degree duct split and have high superheat/sub cooling I think its overcharged with a restriction or a txv out of adjustment...

If you have low airflow from a undersized return, but were taking in 86 degree outside air the unit wouldn't have temperatures that look like that, and your split wouldn't be 26 degrees...Your txv's should be able to deal with 86 degree air and not hit the max of their range...:eek2: