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Discussion Starter · #1 ·
I havent done any hvac work in a couple years and forgot the few things I knew.
I have 410a unit that need to charge back up after a leak search.

it has a piston

right now the low side pressure is at 150 (about 52 degrees) and my suction line temp is 70 degrees.

the head pressure is at 340
and liquid line temp is 100

outdoor temp is about 88
and the heat from condenser is 99.

did I over charge? what could be wrong with the unit plz.
 

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I havent done any hvac work in a couple years and forgot the few things I knew.
I have 410a unit that need to charge back up after a leak search.

it has a piston

right now the low side pressure is at 150 (about 52 degrees) and my suction line temp is 70 degrees.

the head pressure is at 340
and liquid line temp is 100

outdoor temp is about 88
and the heat from condenser is 99.

did I over charge? what could be wrong with the unit plz.
What was the return air temperature - wetbulb and drybulb?
Without this ^, shooting blind.
What was the supply air temperature?

What seer rating?

The numbers do not suggest an over-charge to me, but perhaps other issues like high return air temp/humidity, fan speed too high.
(though i would expect a slightly higher head unless it's a higher seer unit)

Page 26 of https://resources.lennox.com/fileuploads/1f70a5bc-3fc2-4b7d-9d9f-c1d4569f9dddLennox_XC13_IOM.pdf has a chart with typical operating pressures for a 13 seer at different outdoor temps, just as a guide, not to be used for charging.

Were you using a wetbulb temp/outdoor temp superheat chart?
 

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Discussion Starter · #3 ·
What was the return air temperature - wetbulb and drybulb?
What was the supply air temperature?

What seer rating?

The numbers do not suggest an over-charge to me, but perhaps other issues like high return air temp/humidity, fan speed too high.
(though i would expect a slightly higher head unless it's a higher seer unit)

Page 26 of https://resources.lennox.com/fileuploads/1f70a5bc-3fc2-4b7d-9d9f-c1d4569f9dddLennox_XC13_IOM.pdf has a chart with typical operating pressures for a 13 seer at different outdoor temps, just as a guide, not to be used for charging.

Were you using a wetbulb temp/outdoor temp superheat chart?

I dont have a wet bulb Thermometer unfortunately. but the supply air temp is at 65. and the return is at 80 currently.

I think its a 14 seer, not sure.
here are the model numbers for the unit.
condenser
vsx140421aa
evap
aruf42c14ad
 

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I dont have a wet bulb Thermometer unfortunately. but the supply air temp is at 65. and the return is at 80 currently.

I think its a 14 seer, not sure.
here are the model numbers for the unit.
condenser
vsx140421aa
evap
aruf42c14ad
You can get wetbulb temperature by wrapping a regular thermometer probe end in thin fabric material, moistening it and inserting it into the airstream, waiting for it to stablize.

Measure all duct temps as close to air handler as possible.

The wetbulb is essential to get the charge right when there's a fixed orifice, need it to get target superheat.



Your low temperature drop and high suction line temperature could be caused by high humidity in return air. High airflow can do the same thing, but with a 3.5 ton air handler, it doubt that it's too high. In addition, 80F is a relatively high return air temp so I would expect suction to be a little elevated from that alone.
 

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You said your charging after a leak check. What was the condition of the system when starting? Did you pull the charge and have nitrogen in the system? Was there any refrigerant left in the system? If it was empty how low of a vacuum was pulled?
 

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I havent done any hvac work in a couple years and forgot the few things I knew.
I have 410a unit that need to charge back up after a leak search.

it has a piston

right now the low side pressure is at 150 (about 52 degrees) and my suction line temp is 70 degrees.

the head pressure is at 340
and liquid line temp is 100

outdoor temp is about 88
and the heat from condenser is 99.

did I over charge? what could be wrong with the unit plz.
18°f SH
5°f SC.
15°f deltaT
13°f split

If the indoor humidity is 50% RH, then your target SH is 18°f.

Looking fine if you humidity is roughly 50% RH. A tad overcharged if the humidity is higher.
 

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attached.

expected supply air temp.
Is this for this unit and coil? I couldn't find an AHRI match for them. Closest I saw was it paired with a ARUF43D14A

OP is a few degrees off of that. Yea, might need to set the fan speed, since everyone forgets to check that.
 

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Is this for this unit and coil? I couldn't find an AHRI match for them. Closest I saw was it paired with a ARUF43D14A
It's a generic chart.
Obviously shr varies, so does airflow so it won't be right on.
A 15F drop at around 400 cfm per ton, 50% humidity is a bit low imp.
We don't know the real return air humidity though.
 

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It's a generic chart.
Obviously shr varies, so does airflow so it won't be right on.
A 15F drop at around 400 cfm per ton, 50% humidity is a bit low imp.
We don't know the real return air humidity though.
Couldn't tell where is from. Using a phone.

OP is only a few degrees off. Probably needs to adjust airflow as everyone forgets that. If so, probably overcharged a bit.
 

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I have my way to check the CTOA and condensing temperature if I lack some tools, 14 seers should have 20 CTOA to complete condense gas into the liquid, and I always check the liquid temperature at the condenser and make sure it is not 10F higher than temp of ambient air, also make sure the liquid temperature increase btw condenser and evaporator.
For this condenser, the CTOA is low, which means it still has gas without a complete condensing process, the higher the liquid temperature, which means the risk of the evaporator before reaching the metering device.

Again, the very correct checking method for a piston device is according to user_12345a 's suggestion.
 

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I have my way to check the CTOA and condensing temperature if I lack some tools, 14 seers should have 20 CTOA to complete condense gas into the liquid, and I always check the liquid temperature at the condenser and make sure it is not 10F higher than temp of ambient air, also make sure the liquid temperature increase btw condenser and evaporator.
For this condenser, the CTOA is low, which means it still has gas without a complete condensing process, the higher the liquid temperature, which means the risk of the evaporator before reaching the metering device.

Again, the very correct checking method for a piston device is according to user_12345a 's suggestion.
Not too many people use that term, and being a DIY site, even fewer will understand it.

(condensing temperature over ambient)

Low approach or temp over ambient doesn't mean a whole lot except that it's within or not within its operating windows. I use it often, but it isn't definitive at all.
 
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