no superheat, no subcooling

[02powerstroke]

Here is the situation... Design pressures are 150/300psi with 12 degree subcooling...

Actual conditions are 92Psi liquid at a temperature of 69F. High pressure side is at around 220Psi and about 12F BELOW saturation temperature. Cooling isn't really doing much indoors and runs constantly.

Is the compressor on the way out or is there a charge issue here. Forgive me as I am fairly new to the service industry.

Thanks in advance guys

[ChaseAir]

you have 14 deg superheat on r22 at that pressure and temp. The 92 is the suction not the liquid. The liquid (or high pressure or head pressure) temp should read below the saturation temp (it does SUBCOOL the refrigerant after all).

Your suction pressure is kinda high. This could be caused by hot temperature inside or high airflow. Is this a txv system?

[02powerstroke]

R22 is the refrigerant

[zw17]

Here is the situation... Design pressures are 150/300psi with 12 degree subcooling...

Actual conditions are 92Psi liquid at a temperature of 69F. High pressure side is at around 220Psi and about 12F BELOW saturation temperature. Cooling isn't really doing much indoors and runs constantly.

Is the compressor on the way out or is there a charge issue here. Forgive me as I am fairly new to the service industry.

Thanks in advance guys

I am kind of lost in your post...

Fill this out for me:

Refrigerant type (22,410,134)?
Type of system (split, package, chiller)?
Metering device (TXV, orifice, cap tube)?
Suction pressure?
Suction line temp?
Liquid line pressure?
Liquid line temp?
Return air temp?
Temp drop across the evap coil?

This will help us get started.

[02powerstroke]

I'll get to a laptop quick and fill that out..

[ChaseAir]

What is your coil temp difference? Do you have duct leakage to have high suction like that?

[02powerstroke]

I am kind of lost in your post...

Fill this out for me:

Refrigerant type (22,410,134)? R22
Type of system (split, package, chiller)? Split
Metering device (TXV, orifice, cap tube)? TXV
Suction pressure? 92 psi
Suction line temp? 69F
Liquid line pressure? ~220 psi
Liquid line temp? 108F
Return air temp? Didn't measure this, however the thermostat is set to 79F.
Temp drop across the evap coil? Supply air temperature is 67F.
This will help us get started.

I edited the quote to include the requested information

Also, if my suction line pressure is 92psi and my saturation temp is about 57F. If my suction line temperature is 69F, doesn't that mean I have no subcooling?

[Southern Mech]

I edited the quote to include the requested information

Also, if my suction line pressure is 92psi and my saturation temp is about 57F. If my suction line temperature is 69F, doesn't that mean I have no subcooling?

no that means you have 12* superheat. Line temp - Sat temp = superheat for suction and subcool for liquid.

I really reccomend you learn what this is, the superheat / subcool as you can not diagnose a refrigeration issue w/o this. It's kinda like your blood pressure

[zw17]

You have 14*F superheat
You have 0*F subcooling

That 0*F subcooling tells me you are way undercharged.

[knave]

if my suction line pressure is 92psi and my saturation temp is about 57F. If my suction line temperature is 69F, doesn't that mean I have no subcooling?

The suction line is superheated gas returning to the comp from the indoor coil. If sat. temp is 57 and the gas is 69, you have 12F of superheat.

[gregp]

is not adding up here. How can you have 12-14 degree superheat and no subcooling? The TXV will be wide open with no liquid to it, only vapor. S/H should be much higher.

[knave]

is not adding up here. How can you have 12-14 degree superheat and no subcooling? The TXV will be wide open with no liquid to it, only vapor. S/H should be much higher.

Saturated refrigerant can be any combination of liquid and vapor, as long as both are present.

[zw17]

02, have you tried adding gas? I would start by adding until you see you liquid line temp start to drop a bit. No more than 2-3lbs though.

If you don't have the manufactures recommendation on target subcooling I would shoot for 10*F to start. Check your temp drop and superheat and report back to us.

[jpsmith1cm]

Yep..

Add some gas and you will settle down.

Probably even bring your suction pressure down, too.

Bonus points for the OP if he can explain why suction will drop...

[jpsmith1cm]

I really reccomend you learn what this is, the superheat / subcool as you can not diagnose a refrigeration issue w/o this. It's kinda like your blood pressure

I could not agree with this post more.

You NEED to understand subcooling and superheat before you can consider yourself competent in this field.

[02powerstroke]

sorry for the confusion.. yes that is correct, I have about 12F of superheat and a couple degrees of subcooling, at best.. I had to run to grab some parts for another job, but will re-measure in a little while... as for now, I didn't want to add gas just yet.. wanted to be sure

[02powerstroke]

I keep mixing my lines up, and it came out in the form of subcooling/superheat confusion... yes, I have about 12F of superheat coming into the compressor via the suction line... the liquid line has nearly no subcooling to it.. I am going to re-attach the gauges in a bit, when I return to the site, to be sure of my numbers I quoted above.

[waltervan]

Here is the situation... Design pressures are 150/300psi with 12 degree subcooling...

Actual conditions are 92Psi liquid at a temperature of 69F. High pressure side is at around 220Psi and about 12F BELOW saturation temperature. Cooling isn't really doing much indoors and runs constantly.

Is the compressor on the way out or is there a charge issue here. Forgive me as I am fairly new to the service industry.

Thanks in advance guys

Why is the design pressures so high 150PSI suction on R22. Where did you get the design pressures are you sure thats not the testing pressure?

[02powerstroke]

Why is the design pressures so high 150PSI suction on R22. Where did you get the design pressures are you sure thats not the testing pressure?

this was from the manufacturer's information... suction pressure will drop on the suction side when you add refrigerant since you have more refrigerant to absorb heat... since there is more refrigerant you will have more refrigerant to absorb the energy and will result in less liquid refrigerant turning into a gas, or vaporizing

what do I get?

[jpsmith1cm]

this was from the manufacturer's information... suction pressure will drop on the suction side when you add refrigerant since you have more refrigerant to absorb heat... since there is more refrigerant you will have more refrigerant to absorb the energy and will result in less liquid refrigerant turning into a gas, or vaporizing

what do I get?

You get to try again......

:whistle:

[02powerstroke]

how so? It has to do with the heat absorbed by the refrigerant and the vapor pressure of the refrigerant coming back to the compressor... Guess I am a little lost as to what you are looking for here for an answer

[waltervan]

Did I miss the Model Number if not I think we need it

[jpsmith1cm]

how so? It has to do with the heat absorbed by the refrigerant and the vapor pressure of the refrigerant coming back to the compressor... Guess I am a little lost as to what you are looking for here for an answer

Actually, it doesn't have as much to do with heat absorbed as it does with ********.

Damn. I almost gave away the answer.

[02powerstroke]

Greater subcooling

[jpsmith1cm]

Greater subcooling

If you have subcooling, what does that tell you?

What difference would that make in the system?

[02powerstroke]

?

[jpsmith1cm]

?

You don't understand what taking a subcooling reading tells you?

[02powerstroke]

Yes I do, but I'm driving so I am going to have to do this after bit

[jpsmith1cm]

Yes I do, but I'm driving so I am going to have to do this after bit

Drop the phone and hold onto the wheel!

:gah:

Catch you later if I can.

[02powerstroke]

greater subcooling means that you you are below the saturation temp by so many degrees... waht this means is that the refrigerant can absorb more energy before it starts to evaporate... If you have more refrigerant, more subcooling and the same load, you will have less refrigerant turning to a vapor (vaporization) so your vapor pressure will be lower on the suction side of teh compressor... all it means is that you are getting more cooling out of your refrigerant...

Am I missing something without going into enthalpys?

[Southern Mech]

? hmmmm?? design pressures on manufacture label?/? = test pressure, not operating design.


now if we are talking design pressures for operating temps and pressures and they are that high, you have the wrong refrigerant.

[jpsmith1cm]

greater subcooling means that you you are below the saturation temp by so many degrees... waht this means is that the refrigerant can absorb more energy before it starts to evaporate... If you have more refrigerant, more subcooling and the same load, you will have less refrigerant turning to a vapor (vaporization) so your vapor pressure will be lower on the suction side of teh compressor... all it means is that you are getting more cooling out of your refrigerant...

Am I missing something without going into enthalpys?

You're overthinking.

In simple terms, if you measure subcooling, what do you know?

[02powerstroke]

Your refrigerant is a liquid

[ChaseAir]

Your refrigerant is a liquid

It gives you an idea of how much liquid is in the condenser coil. If you had a restriction in the evap area, you might accumulate more refrigerant on the condenser

[02powerstroke]

It gives you an idea of how much liquid is in the condenser coil. If you had a restriction in the evap area, you might accumulate more refrigerant on the condenser

thank you... that makes sense

[02powerstroke]

ok... I went back and tested it one more time.. here is what I ended up with

Suction Line Temperature ~ 60F
Suction Pressure - 83 PSI
Liquid Line Temp - 96F
Discharge Pressure 202psi
Refrigerant - R22

THe model of the condensing unit is a 38CKC042

[ChaseAir]

11 superheat. 6 subcool. It would help to know indoor wb db and delta t.

You have low subcool for sure. If it is a txv metering device, it is most likely undercharged. If it is a piston, you either have low airflow or too big of a piston.

[02powerstroke]

Indoor temp is 78F, will have to measure wet bulb. The consensing unit is a piston unit. This is an original split on a ranch that had the basement finished recently.

[jpsmith1cm]

Your refrigerant is a liquid

Exactly.


And what part of the system needs liquid to operate correctly?

[02powerstroke]

Evaporator coil ;)

[Southern Mech]

Evaporator coil ;)

wrong, be more specific.

[jpsmith1cm]

Evaporator coil ;)

Again, I think you're overthinking.

The TXV requires a solid column of liquid to meter properly.


If it doesn't get that solid column of liquid, it does more than just lose capacity. If the column has enough vapor in it, the valve can't regulate and can cause high suction even though very little cooling is being done.

[02powerstroke]

Thanks again for all the insight... I'm just getting started but plan on learning from this page as a great resource. I'll add some refrigerant and see how the unit performance changes.

[Southern Mech]

Thanks again for all the insight... I'm just getting started but plan on learning from this page as a great resource. I'll add some refrigerant and see how the unit performance changes.

just for learning purposes, and it will not take that much longer, but recover charge and weigh, no need to pull vacurme or add dryer is system not open, then recharge with recovered charge and any additional over and above to what mfg reccomends. And usually its x amount for up to 15' lineset then certain amount for ea addl foot. I am not big on just adding gas on a system I have never worked on before.:.02:

[02powerstroke]

sounds good... I will do that... thanks for the recommendation

[02powerstroke]

well... new twist to the story... the condensing unit fan is now stationary and the liquid line is very hot... what are the chances that the condensing unit fan locked up... its late now here and its dark out so the solution will have be implemented tomorrow... We did have some large lightening storms and heavy rains.... possibility that had something to do with it failing? Seems too coincidental almost

Keep in mind I hadn't recovered any refrigerant or charged teh system up again... it was left as it was from the most recent readings

[lynn comstock]

If you have the old analog gauges, instead of reading pressure read the refrigerant saturation temperature where the needle crosses the R22 ring of numbers around the dial. That makes it far easier to calculate SH and SC.

Using saturation temperatures makes moving from one refrigerant to another painless.
For any PURE refrigerant
The suction gauge tells you the saturation temperature in the evaporator.
The head gauge tells you the saturation temperature in the condenser.


If you have non-condensables in the refrigerant, the high side gauge will read higher than the saturated temperature of the refrigerant when operating, and the low side gauge will read true. That is because the non-condensables get trapped in the condenser by the subcooled liquid refrigerant at the condenser outlet.

[ChaseAir]

well... new twist to the story... the condensing unit fan is now stationary and the liquid line is very hot... what are the chances that the condensing unit fan locked up... its late now here and its dark out so the solution will have be implemented tomorrow... We did have some large lightening storms and heavy rains.... possibility that had something to do with it failing? Seems too coincidental almost

Keep in mind I hadn't recovered any refrigerant or charged teh system up again... it was left as it was from the most recent readings

That'll do It

[02powerstroke]

Yeah, pulled the cap and it's shot... Easy fix

[02powerstroke]

its amazing how things happen all at once... THanks again for everyone who responded to the thread

[tipsrfine]

Yeah, pulled the cap and it's shot... Easy fix

Did you check condition of the fan motor? Any side to side wiggle on the shaft? If so, it should be changed out also. Check the contactor while in there? Take amp readings after replacing the cap and compare it to motors specs? Any wiring looking corroded, showing signs of overheating? Double wall condenser coil? A nice thick blanket between them will fool into thinking your charge is correct if it's a fixed metering device.

[02powerstroke]

Fan motor doesn't have any wiggle... it is aged, but not bad... Has some rust on it...

Contactor is new, looks to have been replaced recently... I will check it anyway...

Wiring looks good, no overheating signs... Unit has a TXV... I will check motor amperage after I replace the cap

[ChaseAir]

If it has txv add r22 until you get 10 subcool or whatever the mfg says. Always (almost) check caps on a service call....and contactor.

[tipsrfine]

One more bit o advice I'd give to a new person is to visit the education forum on this site and read & watch the videos. Good stuff there. Get a digital psychrometer and learn the importance of taking the wet bulb temp of the return air entering the evap, so you can determine what your superheat should be when charging fixed metering devices. You need to know when the superheat should be 5 degrees and when it should be 30 degrees. (This is on the same system mind you).

[02powerstroke]

Thank you... I will check that forum out for sure.

[Capz]

Fan motor doesn't have any wiggle... it is aged, but not bad... Has some rust on it...

Contactor is new, looks to have been replaced recently... I will check it anyway...

Wiring looks good, no overheating signs... I will check motor amperage after I replace the cap

I shoot the temp with my infrared of every fan motor at residential A/C customers home as I am working on their unit. Good motors run at or about 104F on a typical 80F day in PA. I've seen a few read at 145F just prior to failure. Not sure if my theory works is 100% conclusive but its helps to know what may fail in the near future.

[flip67]

Here is the situation... Design pressures are 150/300psi with 12 degree subcooling...

Actual conditions are 92Psi liquid at a temperature of 69F. High pressure side is at around 220Psi and about 12F BELOW saturation temperature. Cooling isn't really doing much indoors and runs constantly.

Is the compressor on the way out or is there a charge issue here. Forgive me as I am fairly new to the service industry.

Thanks in advance guys

Air flow, check for blockage, blower speed every thing that has to do with air flow make sure all vent are open