No superheat!

[ibenek]

Residential split unit 15 years old
TXV R-22
Desired subcooling 17F
liquid line pressure 150psig
actual liquid line temp. 65.5F
Saturated temp. 83f
subcooling 18F

suction line pressure 20 psig!that gives negative 5 F superheat
suction line temp. 72F
Is this TXV mulfunction?
Air flow restriction or something else?

[ibenek]

Sorry mistake negative 5F boiling point

[mark beiser]

That is 77º of superheat, not "no superheat"!

[ibenek]

I just never get to negative part of PT chart so far,but anyway it's very high so It is passible of Air flow restriction thru evaporator or TXV?

[LA1]

You definitely need to check or have someone check to see if you have about 400 CFM of air flow per ton.

[jpsmith1cm]

I can just about promise you that it is not a low airflow problem.

[ibenek]

So what is the problem in the system?any suggestions?
Where should I look for a solution?

[jpsmith1cm]

I would look for a restriction in the system.

[SoFlaDave]

You have extremely high superheat. Low liquid pressure and low suction pressure. If your liquid line temp readings are taken after a drier you may have a partially restricted liquid line drier which would cause the compressor amps to be at or above RLA.

I would probably add a little refrigerant and see if your pressures start rising but keep an eye on the compressor amps while doing this.

[TACKERDOWN]

for your air flow just make sure your indoor fan is not running backwards due to a bad capacitor .

Sent from my PC36100 using Tapatalk

[mofotech]

It can be a laundry list of possibilities:
1)moisture in the system
2)TXV gone bad or dead, including the external equalizer maybe restricted
3)Low refrigerant charge
4)Plugged drier
5) Low refrigerant charge

[jpsmith1cm]

It can be a laundry list of possibilities:
1)moisture in the system
2)TXV gone bad or dead, including the external equalizer maybe restricted
3)Low refrigerant charge
4)Plugged drier
5) Low refrigerant charge

How would a low charge give a good subcooling?

[TACKERDOWN]

Another issue I've seen on the air flow is that the insulation in the blower compartment maybe sucking up against the fan but when you pull the panel off it may fall back against the side of the unit, make sure it is not loose. You may be low on charge.

Sent from my PC36100 using Tapatalk

[jpsmith1cm]

Another issue I've seen on the air flow is that the insulation in the blower compartment maybe sucking up against the fan but when you pull the panel off it may fall back against the side of the unit, make sure it is not loose. You may be low on charge.

Sent from my PC36100 using Tapatalk

How does low airflow cause high Superheat?

[TACKERDOWN]

I shoulda been more specific I was just answering to the question of this air flow not in respect to what is readings were. my bad :beer:

Sent from my PC36100 using Tapatalk

[supertek65]

hopefully he is measuring the subcooling properly?

heck! i usually charge it to 200 lbs head before i even start reading suction line and ll temps!!!!!!!!!!!!!!!!!

65* ll temp???????????????????????????

maybe a restriction actually in the condenser coil itself??????????

[supertek65]

tackerdown,

is your avatar a frozen or iced up unit?
or is it just that color?

[SoFlaDave]

I'd be suspect of any condenser with an internal drier, Goodman, Rheem ,Trane, Lennox pretty much anyone but Carrier. To the OP, remember that the pressures your gauges see may not be what your compressor sees. The "Normal" subcooling you see is likely due to flashing through the drier. The compressor may be pumping well over 200PSIG. Wouldn't hurt to give us indoor and outdoor ambient temp. No such thing as too much info :)

[supertek65]

hi Dave!!!!!!!!!

[mofotech]

How would a low charge give a good subcooling?

Your correct jpsmith1cm.
I over read the part of the subcooling being normal. Oops. Low charge can cause low subcooling and high superheat.

[ibenek]

Thank You all for sudestions.
There is no drier.
Last year start/run capacitor in condenser was changed by other tech.
When condenser is turn off pressure in high and low lines are equal.

[SoFlaDave]

hi Dave!!!!!!!!!

Good day, sir!:cheers:

[SoFlaDave]

Thank You all for sudestions.
There is no drier.
Last year start/run capacitor in condenser was changed by other tech.
When condenser is turn off pressure in high and low lines are equal.

Sounds like an undercharge coupled with a relatively low outdoor ambient. What brand of equipment?

[ibenek]

It's a Cerrier from 1998

[ibenek]

SoFlaDeve It was 69F ambient so It's little low

[SoFlaDave]

Sounds like an undercharge. Do yourself a favor and find the leak. Start at the evap coil. 9 times put of 10 I can find a leaky evap coil by vacuuming out the drain line and finding oil slick traces in the water. It's a time saver.

[crmont]

Check the accumulator for rust and a leak. A sniffer shoved under the base of it works great.

[mofotech]

Sounds like an undercharge. Do yourself a favor and find the leak. Start at the evap coil. 9 times put of 10 I can find a leaky evap coil by vacuuming out the drain line and finding oil slick traces in the water. It's a time saver.

Cool, good tip there Dave.

[skidoox800]

Don't think its low charge, being subcooling is up, and superheat is high. Subcooling would be low if low on charge..

You say no filter drier installed. Restriction at TXV, or TXV malfunction... Airflow I think is ok that superheat is high. I'd check TXV operation with glass of cold water, and holding in your hand. Watch sh/sc then. If it doesnt move i'd say TXV failure.

[ibenek]

Thank You all for responds.
Especially for You So Fla Deve and Crmont.I did some ivastigation and partialy opened the plenum where I saw rust all over the tubing coil

[SoFlaDave]

Restriction at TXV would show high head pressure. Outdoor ambient was only 69* according to OP and liquid temp was only 6* below that. Could be a combination of defective TXV and low charge, but its now the TXV alone.

[mark beiser]

Restriction at TXV would show high head pressure.

Typically a restriction at the TXV, or in the liquid line, will result in lower head pressure. Lower mass flow->lower heat absorbtion->less heat to be rejected-> lower condensing temperature/pressure.
The only reason it would result in higher head pressure is if the system was over charged, or otherwise contains more refrigerant than can be stored in the liquid line and condenser coils, and still leave enough condenser coil volume to condense the refrigerant at normal pressures.

Some newer systems that have micro channel condenser coils, or otherwise have smaller diameter tubing, like Goodmana "smart" coils, naturally contain more refrigerant than can be stored in the condenser, but older systems typically have more than enough volume in the coil and liquid line to very comfortably store the entire refrigerant charge.

[bluecool]

The restriction problem could be something simple. If your service valve has a schrader valve you'll need to back off the back position for your gauges to read correctly. Just a suggestion.

[SoFlaDave]

I'm not quite following you Mark. I agree on some of the points but we're not just absorbing heat from the air we're constantly gained heat from compression and every stroke of the compressor is raising the saturation temp and the pressure.

In my experience a restriction at a point after the service valve shows up as excessive head pressure and low suction.

[beenthere]

Your LL temp is colder then your outdoor temp. is this a heat pump. Sounds like restriction before the area where you took your LL temp.

[beenthere]

I'm not quite following you Mark. I agree on some of the points but we're not just absorbing heat from the air we're constantly gained heat from compression and every stroke of the compressor is raising the saturation temp and the pressure.

In my experience a restriction at a point after the service valve shows up as excessive head pressure and low suction.

Only on long line sets, and systems where someone added gas because of low air flow, or a slight restriction, and they didn't know what the readings were telling them.

[mark beiser]

I'm not quite following you Mark. I agree on some of the points but we're not just absorbing heat from the air we're constantly gained heat from compression and every stroke of the compressor is raising the saturation temp and the pressure.

When there is a restriction, the compressor is moving fewer pounds of refrigerant, thus fewer btu of heat need to be removed to condense the refrigerant, thus less of a temperature difference between the refrigerant and ambient air is needed to remove the heat, thus the condensing pressure/temperature is lower.
The sensible heat gained from compression and the motor windings is chump change in the overall process.


In my experience a restriction at a point after the service valve shows up as excessive head pressure and low suction.

On systems with normal refrigerant line lengths, this would only be true for systems that have been significantly over charged, possibly by someone that previously misdiagnosed the restriction as a low refrigerant charge, and for some newer systems as previously mentioned.

When there is a restriction in the liquid line or metering device, liquid refrigerant stacks up in the condenser coil. This reduces the volume of the coil available for condensing the refrigerant.
With a restriction and normal charge conditions, the remaining reduced coil volume available for condensing refrigerant is still more than enough, because the the volume of refrigerant needing to be condensed is also greatly reduced, so it is able to be condensed at a lower temperature.

In a situation where the system with a liquid restriction has been significantly over charged, the volume of the coil available for condensing refrigerant is reduced to the point that it is to small to condense even the greatly reduced volume of refrigerant at normal condensing temperatures, so the condensing pressure/temperature goes up.

In a long lineset application, with a system that was properly charged, but then developed a restriction at the metering device, the head pressure would run lower than normal because the full length of the LL is still available for storing refrigerant.
If the same long lineset system developed a restriction closer to the condenser, like at the LL filter drier installed near it, the head pressure would behave more like a restriction+overcharge situation.

[SoFlaDave]

That's why this place is so valuable. It shouldn't surprise since alot of the systems I walk up on are over charged before I repair them so that makes sense. Well put gentleman.

[supertek65]

this is accurate!
except after some idiot added an additional 150% overcharge!

guys need to learn how to check amp draw!!!!!!!!!!!!!!

this tells you a lot!

very surprised about the post about poor airflow?






Typically a restriction at the TXV, or in the liquid line, will result in lower head pressure. Lower mass flow->lower heat absorbtion->less heat to be rejected-> lower condensing temperature/pressure.
The only reason it would result in higher head pressure is if the system was over charged, or otherwise contains more refrigerant than can be stored in the liquid line and condenser coils, and still leave enough condenser coil volume to condense the refrigerant at normal pressures.

Some newer systems that have micro channel condenser coils, or otherwise have smaller diameter tubing, like Goodmana "smart" coils, naturally contain more refrigerant than can be stored in the condenser, but older systems typically have more than enough volume in the coil and liquid line to very comfortably store the entire refrigerant charge.

[supertek65]

Dave,
i believe in a cap tube system a low side restriction will cause high head pressure!
pretty sure?
if i am incorrect i am sure i will get my pee pee wacked!

[mark beiser]

Dave,
i believe in a cap tube system a low side restriction will cause high head pressure!
pretty sure?
if i am incorrect i am sure i will get my pee pee wacked!

In a system that was correctly charged before the restriction occurred, it won't, for pretty much the same reasons a LL restriction won't.

The trouble is that the person who finds a restriction usually is not the first person that was there for a low/no cooling call caused by the restriction.
The other guy did a gas and go before you got there. ;)

[servicefitter]

Valve has a bad power head or moisture is high in system and freezing in valve or drier

[supertek65]

you saying gasngo is bad???????????????????????:whistle:






In a system that was correctly charged before the restriction occurred, it won't, for pretty much the same reasons a LL restriction won't.

The trouble is that the person who finds a restriction usually is not the first person that was there for a low/no cooling call caused by the restriction.
The other guy did a gas and go before you got there. ;)

[mark beiser]

you saying gasngo is bad???????????????????????:whistle:

Not after 5pm! ;)

[mofotech]

this is accurate!
except after some idiot added an additional 150% overcharge!

guys need to learn how to check amp draw!!!!!!!!!!!!!!

this tells you a lot!

very surprised about the post about poor airflow?

Very good info here! SuperTek65 when a compressor is pulling excessive amps, what does that indicate to? And I am asking based off refrigeration charge. (LOL, I know I should just look this up in my books, but man sometimes reading online on our forums you learn more then reading the damn chapter 5 times and only picking up a little bit. It's sometimes very boring! Why can't they just get to the point and call it a day! geez)

[supertek65]

if a compressor is drawing rated amps or close, it is doing plenty work and most likely charged properly.
discharge superheat and hot gas temp tells you a lot also



mofotech;12820761]Very good info here! SuperTek65 when a compressor is pulling excessive amps, what does that indicate to? And I am asking based off refrigeration charge. (LOL, I know I should just look this up in my books, but man sometimes reading online on our forums you learn more then reading the damn chapter 5 times and only picking up a little bit. It's sometimes very boring! Why can't they just get to the point and call it a day! geez)[/QUOTE]

[mofotech]

if a compressor is drawing rated amps or close, it is doing plenty work and most likely charged properly.
discharge superheat and hot gas temp tells you a lot also



mofotech;12820761]Very good info here! SuperTek65 when a compressor is pulling excessive amps, what does that indicate to? And I am asking based off refrigeration charge. (LOL, I know I should just look this up in my books, but man sometimes reading online on our forums you learn more then reading the damn chapter 5 times and only picking up a little bit. It's sometimes very boring! Why can't they just get to the point and call it a day! geez)[/QUOTE]


If the windings have started to go bad, will the amps go up? I know the resistance (ohms) measurement will go up if the windings start to go bad.

[supertek65]

I may not be the3 best one to answer this and I may be incorrect??

I will answer it just from experience only.

I am not sure what would cause resistance to actually go UP??? maybe heat?????

In my experience resistance can go down due to turn to turn shorts, maybe the insulation breaking down and of course short to ground and or moisture in the refrigerant.

the lower the resistance the more current, current is amps.

I am not sure I personally have ever seen a motor or winding STARTING to go bad exactly???

if the bearing starts to go bad, usually from oil wash out, the rotor could drag on the stator and I guess you could call that going bad?
that would result in less resistance to ground and more current???

Hopefully this is all correct and it helps,

frank











If the windings have started to go bad, will the amps go up? I know the resistance (ohms) measurement will go up if the windings start to go bad.[/QUOTE]

[mofotech]

I may not be the3 best one to answer this and I may be incorrect??

I will answer it just from experience only.

I am not sure what would cause resistance to actually go UP??? maybe heat?????

In my experience resistance can go down due to turn to turn shorts, maybe the insulation breaking down and of course short to ground and or moisture in the refrigerant.

the lower the resistance the more current, current is amps.

I am not sure I personally have ever seen a motor or winding STARTING to go bad exactly???

if the bearing starts to go bad, usually from oil wash out, the rotor could drag on the stator and I guess you could call that going bad?
that would result in less resistance to ground and more current???

Hopefully this is all correct and it helps,

frank



If the windings have started to go bad, will the amps go up? I know the resistance (ohms) measurement will go up if the windings start to go bad.[/QUOTE]


Sorry, I think your correct. I mixed it up. If the resistance is going down the amperage goes up. Well in class we had a compressor cut open and our teacher was explaining about open,grounded and shorted windings. And he said when the paraffin (which is the insulation on each string of the winding) starts to melt then problems will start occurring down the road. Just like you explained (and it refreshed my memory a bit too) .

[Kevin Weaver]

Residential split unit 15 years old
TXV R-22
Desired subcooling 17F
liquid line pressure 150psig
actual liquid line temp. 65.5F
Saturated temp. 83f
subcooling 18F

suction line pressure 20 psig!that gives negative 5 F superheat
suction line temp. 72F
Is this TXV mulfunction?
Air flow restriction or something else?

150 psi converts to 66 degrees
liquid line temp. 65 degrees
you say 18 degrees of sub cooling
your actual supercooling is 1
It sounds like it needs more charge

[supertek65]

supercooling???????????

dont know what that is but I like it!!!!!!!!!!

[toddfather]

Wow, I think we've seen it all in this thread! I think the candid remarks by jpsmith pretty well nailed the coffin lid shut on this problem.

[xpuser357]

:ditto:

[david912]

YOur not low on charge, your subcooling is good, You have a restriction in drier or txv, probley txv. Also if you had an airflow problem your superheat would be 0, you would have a low suction psi and no superheat not a 77* superheat, and if your blower was running backwards you would immediatly freeze, it would be a block of ice change your txv and the drier along with it.

[david912]

YOur probley not low on chrage and your blower is not running backwards or it would be a block of ice. Also you probly do not have an airflow problem with a 77* superheat, your superheat would be 0 with an airflow problem.. low airflow= low superheat. if you have an airflow problem you will have low suction psi and low to no superheat. you are probley looking at a restiction in txv or drier, usually with a restriction you will have high superheat, high subcooling, but there no telling how many hands have been on the equipment your working on and people do some crazy things. but i would change the txv and drier with it. you might end up a little bit undercharged after repairs are made. keep it mind you can always have more than one problem.

[david912]

sorry made some corrections to the first post disregard that one

[sabur2121]

From what your saying is kind of confusing, according to the numbers. What I would do is check for a restriction in the liquid line drier by measuring the temp in front and the back side of the drier. If you have a temp difference then the restriction is the drier. That would be the first step. If everything checks out fine then proceed to the next step by recovering the refrigerant and changing the TXV. Your subcooling seems to be just a tap bit high but not a real concern. What is your dry and wet bulb temp? This is another factor to consider as well.

[millertime77]

Very good info here! SuperTek65 when a compressor is pulling excessive amps, what does that indicate to? And I am asking based off refrigeration charge. (LOL, I know I should just look this up in my books, but man sometimes reading online on our forums you learn more then reading the damn chapter 5 times and only picking up a little bit. It's sometimes very boring! Why can't they just get to the point and call it a day! geez)

High superheat will give you lower amps, low superheat will give you higher amps. With higher super heat the vapor is less dense so compressor doesn't work as hard, low superheat = more dense refrigerant and more work for compressor. It's like setting a CPR valve.

[tedwasright]

I'm very new to the field but I agree with beenthere. Suction line temperature (72*) is higher than the liquid line temperature (65*). Like I said I am new so be kind if I'm retarded by accident.

That is crazy superheated so obviously the evaporator isn't getting the refrigerant it needs. Assuming proper airflow, and that the sensing bulb is fixed properly, and that the proper procedures were followed in collecting the information I'd look first at the TXV and determine if it's working properly or at all. But if there isn't a filter drier installed then the installation wasn't done correctly. I would then assumed that there are probably noncondensables in the system. I'd do a standing pressure test. Then pump down, install a filter drier, take the TXV apart and pull a triple evacuation.

Again, please forgive my novice approach and be kind. I am trying.