Low Charge Indication w/o Pressure Readings?

[WillieOH]

I have a brand new rheem a/c 14 seer, 2 ton with 800 cfm at evaporator. Seems to work great, but the liquid line always seems around room temp even at 93 odt. I would think a little warm would be expected. Drop across evaporator coil is 20F and steady (once saw 23F). 75 idt. 50% RH. This drop is seen just minutes after startup. I'm wondering if I have a low charge. Would these observations indicate that or does this sound normal?

[martyinlincoln]

Sounds like you need the installer back out to check things over. Liquid line at 75 degrees with a 93 odt isn't right.

[Chris_Worthington]

Got some readings that actually mean something here??? :whistle:

SC ? SH ? DSH ?

[chuckcrj]

Need to measure the liquid line temp with a clamp or strap on thermometer.

If it is indeed cooler than ambient you have a problem, and not low charge.

BTW how did you get it to exactly 800 CFM?

[mason]

I have a brand new rheem a/c 14 seer, 2 ton with 800 cfm at evaporator. Seems to work great, but the liquid line always seems around room temp even at 93 odt. I would think a little warm would be expected. Drop across evaporator coil is 20F and steady (once saw 23F). 75 idt. 50% RH. This drop is seen just minutes after startup. I'm wondering if I have a low charge. Would these observations indicate that or does this sound normal?

What does room temp mean? Is the line temperature literally 75 degrees or is it just not warm in your hand, which would be your body temp. Some signs of low charge are ice forming on suction line, air that feels cool blowing out of condenser, gradual loss of airflow(due to ice). You havn't listed any of these but your info is not sufficient to give you any suggestions.

[WillieOH]

What does room temp mean? Is the line temperature literally 75 degrees or is it just not warm in your hand, which would be your body temp. Some signs of low charge are ice forming on suction line, air that feels cool blowing out of condenser, gradual loss of airflow(due to ice). You havn't listed any of these but your info is not sufficient to give you any suggestions.

It means not warm to the touch. It's a subjective measurement. However, researching this a little, I may actually have a mild overcharge of r410a. The txv is regulating to provide a good super heat, causing the excess liquid to build up in front of the txv, in the condenser, allowing it to sub cool excessively.

If I had a low charge, but still enough to allow the txv to do its job, the liquid line should be warmer than normal or hot, according to what I've read. Does this make sense?

I'll probably hook up my manifold at some point. I just hate dealing with 410a blowback if I don't have to..

The condenser is blowing mild temp air. Much cooler than my old 1991 trane 2.5 ton with r-22 would typically blow. I just figure that is because of the higher efficiency of the 410a. Does that sound right?

[WillieOH]

Need to measure the liquid line temp with a clamp or strap on thermometer.

If it is indeed cooler than ambient you have a problem, and not low charge.

BTW how did you get it to exactly 800 CFM?

I guess the liquid line could be odt or a bit above. The 800cfm came from my furnace sensors. High end Rheem. It uses a factory calibrated variable speed blower assuming TSP<0.6". Actual display was 798.

[WillieOH]

Got some readings that actually mean something here??? :whistle:

SC ? SH ? DSH ?

Sorry, but if I had those numbers, I would also have my answer :)

I was hoping to tap into the vast experinces from the community.

[rickboggs]

I don't think willieoh has a problem, by the way, I love my dog too.

[WillieOH]

I don't think willieoh has a problem, by the way, I love my dog too.

Thanks Rick! So what I'm seeing is typical of a 410a system? I'm so used to the older trane over the years.

[rickboggs]

Thanks Rick! So what I'm seeing is typical of a 410a system? I'm so used to the older trane over the years.
7 degree sub cool plus or minus 2 degrees. If my head pressure is 340psi, my saturation temperature is a around 105 degrees, minus 7 degrees sub cool... 100 to 96 degrees? I can't measure that with the touch of my hand.

[GAC]

Ideal subcool can differ depending on the manufacturer and efficiency of your unit. It would probably be a good idea to check the mfg specs and use that as your target temps/pressures, or better yet have your installer come check the charge for you.

[udarrell]

I have a brand new rheem a/c 14 seer, 2 ton with 800 cfm at evaporator. Seems to work great, but the liquid line always seems around room temp even at 93 odt. I would think a little warm would be expected. Drop across evaporator coil is 20F and steady (once saw 23F). 75 idt. 50% RH. This drop is seen just minutes after startup. I'm wondering if I have a low charge. Would these observations indicate that or does this sound normal?
A 14-SEER; 2-Ton; R410A system, at 75F db, 63F wb 800-cfm @95F OAT; @ indoor conditions of 75F db, 63F wb, 51.76 % RH - will yield 375-psig head; around 112.5F SCT minus say mfg'ers minus 10 subcooling is 102.5F LLT.

A human body at 98.7F would make it difficult to distinguish the difference in temp by touch, either outdoors or indoors; touch is NOT room temp.

I would think if the indoor drop is right-on compared to the humidity reading & on-target airflow; I doubt I'd worry excessively about the systems charge.
You need more definitive testing to be reassured of an accurate charge...

[amd]

The txv is regulating to provide a good super heat, causing the excess liquid to build up in front of the txv, in the condenser, allowing it to sub cool excessively.


It's physically impossible to subcool refrigerant below ambient with an air cooled condenser coil.

TXV systems are charged by sub-cooling.


The condenser is blowing mild temp air. Much cooler than my old 1991 trane 2.5 ton with r-22 would typically blow. I just figure that is because of the higher efficiency of the 410a. Does that sound right?


It has nothing to do with the refrigerant.

Manufacturers use larger coils to reduce the compression ratio; as a result, the head pressure and temperature is lower on your new system. The energy consumed by the compressor gets absorbed by the refrigerant in the form of heat; lower compressor amp draw = cooler refrigerant + lower heat dissipation.

[mason]

Willieoh, you might just be better off checking the temp drop across your indoor coil with a temp probe just before and after the coil. It sounds like you don't have low loss hoses or pipe probes so one you could get a nasty burn and two you will only be able to check pressures which could be off due to not calibrating your gauges. If you have a good temp drop then I wouldn't worry about it.

[chuckcrj]

It's physically impossible to subcool refrigerant below ambient with an air cooled condenser coil.



Ahh, but it is possible to have a liquid line temps below outdoor ambient.....

[WillieOH]

Thanks all for all the feedback.

I should never have said 'room temp'. That got alot of attention! I meant 'not hot', as compared to my old r-22 trane unit of 20 yrs, no one would have known that's what I meant..

The only reason I got concerned was I felt a cooler than normal liquid line, and condenser air flow and evaporator temp drop (20F vs. 18F) than I was used to seeing with the old system. Btw, I removed the panel on the evaporator at the end of cycle and saw no icing at all , so seems there's no problem.

Also, thanks for explaining why new systems run cooler. Makes sense now.

[WillieOH]

Ahh, but it is possible to have a liquid line temps below outdoor ambient.....

Do you mean a restricted liquid line, too much braze or something causing a pressure drop on the way to the txv?

[WillieOH]

Willieoh, you might just be better off checking the temp drop across your indoor coil with a temp probe just before and after the coil. It sounds like you don't have low loss hoses or pipe probes so one you could get a nasty burn and two you will only be able to check pressures which could be off due to not calibrating your gauges. If you have a good temp drop then I wouldn't worry about it.

I do have low loss hoses (valves on the ends). I just hate any blowback. R-22 was bad enough :)