A/c unit not cooling

[johnnyirish11]

Hey, I need some help on this one. I have a 2.5 ton unit with condensor unit working and an air handler that the unit is working. Everything runs. Pressure is at 70 low and 195 high. I get no condensation on the low side line and a faint warmness on the high side line. Thermostat is set at 73 and room temp is reading 80 deg. I put a thermometer in the vent and the cool air coming out is 70 deg. The apartment is not cooling down. I added some ***** to the system to get up to 100 psi on the low side and this had the low side line sweating with condensate, but i know it is not healthy to have that high a press reading. Coils are clean, filter is new. Any suggesstions would be great. If you need any other info please let me know. :confused:

[Brian_UK]

Any idea what the gas is? 'cos we haven't. ;)

[johnnyirish11]

Any idea what the gas is? 'cos we haven't. ;)




Yes sorry unit is R 22

[goshen]

Yes sorry unit is R 22
Hi:
your high side is low, should be at aprox - 220-250 psi ,you should have some sort of pressure control,by adding too much refrigerant you probably floded the condenser,evacuate the sys and charge by wheight or pressure correctly .:)
good luck

[johnnyirish11]

How do I tell if there is a restriction? I will try to evac today and recharge system

[Pilotman]

I'm a new member so, sorry to jump your post Johnny, but this looked like the place to start. I'm supposed to know this stuff but am having a similar problem with my own unit. Just replaced 2.0 ton 10 SEER evap and condenser R-22 with 2.0 ton 13 SEER R-22 condenser and coil (matched set). Filter is clean. New dryer on liquid side near evap coil. Used the orifice that came with new unit (size was correct per chart). Line set is about 30 feet - didnot add refrigerant to the factory charge. Now I'm only getting 17.5 degrees drop across the coil (at the coil). With unit at steady state running for over an hour: 89 degree ambient, 102 condenser discharge temp, 61% humidity, 75 degree interior (no hum check), 205 psi liquid line, 75 psi suction line, liquid line temp 88-89, Superheat appears to be 16 degrees, RAT at coil - 78.5 (attic unit - must assume some leaky ductwork - 1990 install date), SAT at coil 61.0. This thing is whupping my tail. The system was only open to atmosphere for about an hour. I pulled a deep vaccume and held it for several hours. Charged with dry nitrogen - to 250 - watched for an hour - no drop. What am I missing? Is the orifice too large? My high side appears low. But the low side looks high. To me that says I'm flowing too much refrigerant through the evap. If so, what size should the orifice be?

[nike123]

How do I tell if there is a restriction? I will try to evac today and recharge system

Restriction could be spotted where temperature of line before and after restriction is different more than 1°F.

For proper evaluation we need this readings:

Evap air/water in temp
Evap air/water out temp
Low side pressure or saturation temp
Suction line temp at evap outlet
Suction line temp at compressor inlet

Cond air/water in temp
Cond air/water out temp
High side pressure or saturation temp
Liquid line temp at receiver or condenser outlet
Liquid line temp at TXV/ inlet




The more information provided the more accurate the diagnosis.

[nike123]

I'm a new member so, sorry to jump your post Johnny, but this looked like the place to start. I'm supposed to know this stuff but am having a similar problem with my own unit. Just replaced 2.0 ton 10 SEER evap and condenser R-22 with 2.0 ton 13 SEER R-22 condenser and coil (matched set). Filter is clean. New dryer on liquid side near evap coil. Used the orifice that came with new unit (size was correct per chart). Line set is about 30 feet - didnot add refrigerant to the factory charge. Now I'm only getting 17.5 degrees drop across the coil (at the coil). With unit at steady state running for over an hour: 89 degree ambient, 102 condenser discharge temp, 61% humidity, 75 degree interior (no hum check), 205 psi liquid line, 75 psi suction line, liquid line temp 88-89, Superheat appears to be 16 degrees, RAT at coil - 78.5 (attic unit - must assume some leaky ductwork - 1990 install date), SAT at coil 61.0. This thing is whupping my tail. The system was only open to atmosphere for about an hour. I pulled a deep vaccume and held it for several hours. Charged with dry nitrogen - to 250 - watched for an hour - no drop. What am I missing? Is the orifice too large? My high side appears low. But the low side looks high. To me that says I'm flowing too much refrigerant through the evap. If so, what size should the orifice be?


Higher SEER mean lower coil dT. That also mean little higher evaporation and little lower condensation than on 10 SEER coils.
Superheat is 8K (16°F) which look OK to me for your conditions, if we presume that indoor humidity is also near 60% (Indoor WB 65°F) .
You can evaluate your system by measuring air flow across evaporator and by measuring air temperature and humidity before and after coil.

If you have correct airflow of 800 FPM and about 3 l/h condensate, your evaporator coil achieves 2 Ton of duty with that dT.

[Pilotman]

Wow, thanks for the quick response. I measured via aneometer (sic) fpm at each supply, totaled and divided by # of supply's x sq ft id of the coil box and got 720 cfm - given leakage and the error factor the actual cfm is at least 800 cfm.

I didn't check the orifice but it must be right - they would not ship anything much larger than a 063 for 24,000 Btu. I suppose I'll check that eventually.

Maybe i'm just not going to see more than 17 or 18 dT at the coil on this 13 seer unit.

Relative humidty was about 55%.

Next time I get worked up, I'll check the orifice size.

Thanks again!

[hvacrmedic]

Hey, I need some help on this one. I have a 2.5 ton unit with condensor unit working and an air handler that the unit is working. Everything runs. Pressure is at 70 low and 195 high. I get no condensation on the low side line and a faint warmness on the high side line. Thermostat is set at 73 and room temp is reading 80 deg. I put a thermometer in the vent and the cool air coming out is 70 deg. The apartment is not cooling down. I added some ***** to the system to get up to 100 psi on the low side and this had the low side line sweating with condensate, but i know it is not healthy to have that high a press reading. Coils are clean, filter is new. Any suggesstions would be great. If you need any other info please let me know. :confused:

Why don't you just call a pro? At this rate you'll be replacing a compressor soon.

[unicorn77]

you sytem is have a air lock, check you cooling tower water..

[Gary]

Wow, thanks for the quick response. I measured via aneometer (sic) fpm at each supply, totaled and divided by # of supply's x sq ft id of the coil box and got 720 cfm - given leakage and the error factor the actual cfm is at least 800 cfm.

I didn't check the orifice but it must be right - they would not ship anything much larger than a 063 for 24,000 Btu. I suppose I'll check that eventually.

Maybe i'm just not going to see more than 17 or 18 dT at the coil on this 13 seer unit.

Relative humidty was about 55%.

Next time I get worked up, I'll check the orifice size.

Thanks again!

Assuming all else is working properly, the dT is a function of airflow. Lowering the airflow raises the dT. Raising the airflow lowers the dT.

If you want to get the dT up to 20F, lower the fan speed... but keep in mind that lower fan speed (higher dT) decreases your efficiency, while higher fan speed (lower dT) removes less humidity from the air. If you are happy with the humidity level, you may want to leave it as is.

[Gary]

Hey, I need some help on this one. I have a 2.5 ton unit with condensor unit working and an air handler that the unit is working. Everything runs. Pressure is at 70 low and 195 high. I get no condensation on the low side line and a faint warmness on the high side line. Thermostat is set at 73 and room temp is reading 80 deg. I put a thermometer in the vent and the cool air coming out is 70 deg. The apartment is not cooling down. I added some ***** to the system to get up to 100 psi on the low side and this had the low side line sweating with condensate, but i know it is not healthy to have that high a press reading. Coils are clean, filter is new. Any suggesstions would be great. If you need any other info please let me know. :confused:

The air temp at the vent just won't do. We need to know the air temps, in and out, as close to the air handler (AHU) as possible. Usually on a ducted system there is a flexible duct connector at the AHU and this provides a handy place to poke a tiny hole and insert your thermometer.

Adding refrigerant was a big mistake. :(

[goshen]

Hi
look at the dates!

[Gary]

Late to the party again... story of my life... lol

[goshen]

Hi
it seems like this guy was on a writing frenzy,never seen anybody answer 14 old threads on one shot ,and it is never to late to party so bring the beer on !
take care gary

[Brian_UK]

Hi
it seems like this guy was on a writing frenzy,never seen anybody answer 14 old threads on one shot ,and it is never to late to party so bring the beer on !
take care gary
Just waiting for the eventual URL Link or similar post once he reaches 15 posts. ;)

[Gary]

Hi
it seems like this guy was on a writing frenzy,never seen anybody answer 14 old threads on one shot ,and it is never to late to party so bring the beer on !
take care gary

I watched a TV show recently called "How beer saved the world". Interesting stuff. Turns out beer is what began civilization by starting agriculture. The first known crop was barley, which everyone assumed was used to make bread, but in fact it was cultivated 300 years before bread was invented and examination of pottery used in that area during that time period showed barley/beer residue. They were using the barley to make beer.

The show went on to very plausibly demonstrate how a long list of advances in human development were directly or indirectly brought about by the quest for beer, from the building of the pyramids to the discovery of germs/pastuerization to the beginnings of automation and the elimination of child labor.

[goshen]

HI
now we know it really isnt never to late to party,what a choice bread or beer????