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bryantman21
08-29-2011, 12:52 PM
I am working on a ruud heat pump MN# upne-048jaz with an electric air handler inside mn#uhla-hm48 with R-22 coil mn#rcsa-hm4824au. The home owner called with a complaint of freezing up on hot days with 85 degrees and up. Unit is 4 years old and this is the first hot summer we have had since it's install (not an install of mine). With 80 degree ambient outdoor it has 180# head, 50# suction with 50 degree line temp. We sucked it down and purged with nitrogen and vacuum and weighed in a new charge. Checked the pressure drop across filter drier and all seems to be well there. Replaced txv and no change with that either. Have cycled unit into heat mode in hopes that if there was oil in distributor tubes when in heat mode i do have a slight pressure difference from each port. Any ideas?

wspascoe
08-29-2011, 02:22 PM
Check airflow and ductwork I had one beginning of summer rtn duct would suck shut when running

dunkman
08-29-2011, 03:32 PM
Check static pressures in ductwork, for starters.

bryantman21
08-29-2011, 04:24 PM
I should have mentioned I have done that, that was the first thing we did. I am starting to lean towards a check in the outside txv that is not opening, also on this ruud there are small strainers braized in on either sid of the txv outside. possibly a issue there but i dont have a noticiable temperature change from one side to the other of the strainers, but maybe i am wrong in thinking i should. trying to decied what the next move should be or if im missing something.

Thomasg
08-29-2011, 05:27 PM
Txv? Sure its not undercharged? , check subcool and delta T that will let you know if its refrigerant problem or airflow. Need to know subcool?

McLean Air
09-04-2011, 04:11 PM
I would think an under charged system would freeze when outdoor temps are lower. Like at night. Although a/c's run 24/7 here all summer. I had one that would freeze up sometimes. When I got there and thawed it out it would run fine for weeks. I did not even look at the contactor. I managed to catch it stuck on. Such a simple fix and it took me a few return trips to check. I was so sure it was a charge or air flow issue, I skipped the basics. That was a fun one to explain to my boss. lol

bob_scheel
09-04-2011, 06:52 PM
What's your superheat at the expansion valve bulb? If its good or low then you have an airflow problem, or a plugged evaporator coil. Might also be a improperly sized coil, but your model #'s seem to indicate its matched.

If you are getting a high superheat then the txv isn't feeding enough refrigerant causing the low suction. (and consequently the low head pressure)

HJ Controls
09-04-2011, 09:02 PM
need info unless you want a bunch of guessing and part changing.
whats your superheat and whats your subcooling.
if you want refrigerant diagnosis this is the info you will always need to give.
if you want a guess then check return air duct and grill sizes, coil dirty, low charge or wrong condenser fan motor. ie 1175 when an 820 rpm motor is oem.

PalmettoMaintPro
09-04-2011, 09:25 PM
I used to work for a Rheem dealer , I have seen the out door txv cause the same symptoms you are talking about . :putergreet:

MetroAir
09-05-2011, 12:07 AM
I agree to check static pressure. If it's 80 degrees out with only 50/180 it seems to be undercharged. Once temps drop at night, that would cause it to freeze up. Everyone else gave good input too. Check sub and superheat...and split before replacing more parts. Good luck!

ckartson
09-05-2011, 12:17 AM
when you said you weighed in the charge, where are you getting the data?

meoberry
09-05-2011, 12:24 AM
I agree to check static pressure. If it's 80 degrees out with only 50/180 it seems to be undercharged. Once temps drop at night, that would cause it to freeze up. Everyone else gave good input too. Check sub and superheat...and split before replacing more parts. Good luck!

What he said.:.02:

PalmettoMaintPro
09-06-2011, 11:29 PM
when you said you weighed in the charge, where are you getting the data?

Just noticed you said weighed in . If the plate on the unit says 4.5 lbs, That is the factory charge the unit has when it is shipped to us if I am not mistaken. Add 25 to 30 ft of line set and indoor coil , a "weighed in charge" of what the outdoor units name plate says would result in an under charge . And probally save you a bunch of time checking all the duct stuff, Not saying it is a bad idea to check ,I have just seen really simple stuff cause guys a lot of heart ache , And spending three or so hours or how ever long checking this and that when it was a simple oversight .My thought is if you weighed in a charge according to that plate on the condenser ,you are defintely under charged espcially if it has a long line set or a larger size air handler to get the higher seer. :cheers:Please excuse my spelling ,it has been one of those days:gah:

PalmettoMaintPro
09-06-2011, 11:42 PM
Sorry to be a thread hog just my brain is cooking this one. Split systems are best charged by subcool or superheat IMO. Weighing a charge should be for something that there is not a variable in ,i.e. ice machines and package units or fridges. The line set of a split system is a variable unless you know for a fact EXACTLY how long the lines are. Which makes weighing a charge for a split a tad trickier to do. It can be done ,but only with accurate math.

Chuck
09-07-2011, 12:12 AM
I should have mentioned I have done that, that was the first thing we did. I am starting to lean towards a check in the outside txv that is not opening, also on this ruud there are small strainers braized in on either sid of the txv outside. possibly a issue there but i dont have a noticiable temperature change from one side to the other of the strainers, but maybe i am wrong in thinking i should. trying to decied what the next move should be or if im missing something.

You checked static, what was it?

You have low airflow or refrigerant restriction, but you will have to give us SC and SH to know for sure which.

sgagne199
09-15-2011, 08:07 PM
if the txv was not feeding properly or you had a restriction in the system wouldn't you see higher head pressures than normal and 180 is certainly lower than normal for 22. sounds to me you either have low load aka airflow or low refrigerant charge

TriWorksInc
09-15-2011, 08:27 PM
I had a Ruud heatpump this summer that I went on a no cooling call to find the indoor expansion valve slammed closed, thought it was a slam dunk diagnosis, but nooo. I put the new expansion valve in, and blam the same freekin problems, same issues presented. After doing major testing and checking. The second expansion valve was bad. Ruud sent me a new one (3rd) and the problem was solved. Crap Happens, I thought only to me!

PalmettoMaintPro
09-15-2011, 08:36 PM
I had a Ruud heatpump this summer that I went on a no cooling call to find the indoor expansion valve slammed closed, thought it was a slam dunk diagnosis, but nooo. I put the new expansion valve in, and blam the same freekin problems, same issues presented. After doing major testing and checking. The second expansion valve was bad. Ruud sent me a new one (3rd) and the problem was solved. Crap Happens, I thought only to me!

I saw a bad one in couple of new Rheems , Txv that is . guess it can happen to any brand though , dont wanna rheem bash , worked for a dealer for a year . they make a really solid product . as does Ruud, which are restickered Rheems in a nut shell

TriWorksInc
09-16-2011, 07:52 AM
I was just letting him know that there is always a possibility that a new part is bad. Ruud is a solid piece of equipment and they do not make the expansion valves, but they stood behind there equipment warranty and there tech support helped too.

PalmettoMaintPro
09-16-2011, 11:46 PM
I was just letting him know that there is always a possibility that a new part is bad. Ruud is a solid piece of equipment and they do not make the expansion valves, but they stood behind there equipment warranty and there tech support helped too.

agreed whole heartedly , Rheem and Ruud are always great as far as warranting thier equipment
:cheers:

timebuilder
09-17-2011, 07:45 AM
What is the return air temp?

In cooling mode, you need to get heat into the refrigerant in the indoor coil. If you have low suction pressure in cooling mode, then you are not getting enough heat in there, most likely because of poor return airflow.

Post return air temp, static across the evap, and subcooling.

Make sure the txv is properly installed, bulb correct and tight. You can test the txv using ice water and warm water, dunking the bulb.

Ford3517
09-17-2011, 08:44 PM
if the txv was not feeding properly or you had a restriction in the system wouldn't you see higher head pressures than normal and 180 is certainly lower than normal for 22. sounds to me you either have low load aka airflow or low refrigerant charge

From what I was taught and my experience, the only restriction that should give you a high head pressure would be a compressor discharge line restriction. A restriction anywhere after the condenser would not result in a high head pressure. When you pump a system down you completely block the flow of refrigerant and you do not get a high head pressure. Refrigerant condenses and turns to liquid and once the low side is in a vacuum there is nothing left to pump.

PS I should add that in some cases this may not be true but most of the time it is.

timebuilder
09-17-2011, 09:01 PM
From what I was taught and my experience, the only restriction that should give you a high head pressure would be a compressor discharge line restriction. A restriction anywhere after the condenser would not result in a high head pressure. When you pump a system down you completely block the flow of refrigerant and you do not get a high head pressure. Refrigerant condenses and turns to liquid and once the low side is in a vacuum there is nothing left to pump.

PS I should add that in some cases this may not be true but most of the time it is.

Here we go again.....:whistle:

PalmettoMaintPro
09-17-2011, 10:08 PM
From what I was taught and my experience, the only restriction that should give you a high head pressure would be a compressor discharge line restriction. A restriction anywhere after the condenser would not result in a high head pressure. When you pump a system down you completely block the flow of refrigerant and you do not get a high head pressure. Refrigerant condenses and turns to liquid and once the low side is in a vacuum there is nothing left to pump.

PS I should add that in some cases this may not be true but most of the time it is.


if the suction line is stopped up,(unlikely,but ya never know) the head pressure is still going to be high because it can't get thru the suction line ,backing up and resulting in high head pressure. When you pump a unit down the compressor and every thing is assumed to be working fine the reason you dont see the head pressure going up when you pump down a unit is because the accsess port is AFTER the shut off valve. It is physics,when the pump runs it is pushing liquid and pulling vapor and any blockage in between said push and pull ports is going to adversly effect pressure. A restriction is usually going to cause the symptoms orriginally described in this thread . Cause if that pump is still pumping and it cant get thru to the pump return , the pressure is going to rise BEHIND the point of blockage and the pressure AFTER the blockage is going to be low. Remember the lines make a loop to an from the compressor being that that is where the magic happens. The whole pump down thing is bad example IMO. I base this on what I said about the accsess port being being AFTER the valve

bob_scheel
09-18-2011, 12:58 AM
if the suction line is stopped up,(unlikely,but ya never know) the head pressure is still going to be high because it can't get thru the suction line ,backing up and resulting in high head pressure. When you pump a unit down the compressor and every thing is assumed to be working fine the reason you dont see the head pressure going up when you pump down a unit is because the accsess port is AFTER the shut off valve. It is physics,when the pump runs it is pushing liquid and pulling vapor and any blockage in between said push and pull ports is going to adversly effect pressure. A restriction is usually going to cause the symptoms orriginally described in this thread . Cause if that pump is still pumping and it cant get thru to the pump return , the pressure is going to rise BEHIND the point of blockage and the pressure AFTER the blockage is going to be low. Remember the lines make a loop to an from the compressor being that that is where the magic happens. The whole pump down thing is bad example IMO. I base this on what I said about the accsess port being being AFTER the valve

A suction line restriction won't cause high head pressure. The condenser will just condense the additional refrigerant. Then as the suction drops the head will also drop.

bob_scheel
09-18-2011, 01:02 AM
From what I was taught and my experience, the only restriction that should give you a high head pressure would be a compressor discharge line restriction. A restriction anywhere after the condenser would not result in a high head pressure. When you pump a system down you completely block the flow of refrigerant and you do not get a high head pressure. Refrigerant condenses and turns to liquid and once the low side is in a vacuum there is nothing left to pump.

PS I should add that in some cases this may not be true but most of the time it is.

On systems without a receiver (or too small of one) a liquid line restriction could cause high head pressure if the line set is long enough after the restriction to cause the condenser to flood.

Ford3517
09-18-2011, 01:14 PM
if the suction line is stopped up,(unlikely,but ya never know) the head pressure is still going to be high because it can't get thru the suction line ,backing up and resulting in high head pressure. When you pump a unit down the compressor and every thing is assumed to be working fine the reason you dont see the head pressure going up when you pump down a unit is because the accsess port is AFTER the shut off valve. It is physics,when the pump runs it is pushing liquid and pulling vapor and any blockage in between said push and pull ports is going to adversly effect pressure. A restriction is usually going to cause the symptoms orriginally described in this thread . Cause if that pump is still pumping and it cant get thru to the pump return , the pressure is going to rise BEHIND the point of blockage and the pressure AFTER the blockage is going to be low. Remember the lines make a loop to an from the compressor being that that is where the magic happens. The whole pump down thing is bad example IMO. I base this on what I said about the accsess port being being AFTER the valve

It doesn't matter that the service port is after the valve. I have pumped systems down with a solenoid valve leaving the service port open the gauge. I didn't believe my teacher when he said a restriction wouldn't cause a high head pressure so I did it and the head pressure did not go up.


A suction line restriction won't cause high head pressure. The condenser will just condense the additional refrigerant. Then as the suction drops the head will also drop.

I agree


On systems without a receiver (or too small of one) a liquid line restriction could cause high head pressure if the line set is long enough after the restriction to cause the condenser to flood.

I also agree, and I am not intending to be rude but I did put a PS disclaimer to note that what I posted was not always the case. Please don't think I am stepping on any toes because I know I don't know everything and I learn a lot just lurking around here. :cheers:

PalmettoMaintPro
09-18-2011, 03:04 PM
I am sorry but I still stand by the physics of it , If a line some thing goes thru is stopped up no matter where it is in the system is going to cause some type of adverse/unwanted operating condition and pressure changes . I am one of those have to see to believe it guys and the pumpdown test just does not make sense to me. A hot gas valve for instance if I am not mistaken traps a small amount of hot gas out of the compressor before it goes into the condenser and stores it behind the H/G valve and then the gas is used during the defrost cycle of ice machines and other types of refrigeration applications. My point is that we are creating a little electrically controlled mini restriction and using it to our advantaged ,but it is controlled and planned and therefore does not create any adverse or unwanted operating conditions. Which IMO an uncontrolled line restriction is going to cause some type of pressure change somewhere in the system. I realize that refrigerant is a strange beast sometimes especailly in large quantities or in elaborate piping schemes where it changes state many times . But physical space is physical space and only so much any thing can fit in a predetermined space . Also I wanna say that I do NOT know it all ,I just think simple things should be kept simple. I am always willing to learn new things and feel like knowledge is the best tool any tech can have. Sorry if I sound"that way" I just feel like right is right and when there is an equation that does not have variables ,there should be none added for the sake of conversation.

Chuck
09-18-2011, 03:15 PM
I am sorry but I still stand by the physics of it , If a line some thing goes thru is stopped up no matter where it is in the system is going to cause some type of adverse/unwanted operating condition and pressure changes . I am one of those have to see to believe it guys and the pumpdown test just does not make sense to me. A hot gas valve for instance if I am not mistaken traps a small amount of hot gas out of the compressor before it goes into the condenser and stores it behind the H/G valve and then the gas is used during the defrost cycle of ice machines and other types of refrigeration applications. My point is that we are creating a little electrically controlled mini restriction and using it to our advantaged ,but it is controlled and planned and therefore does not create any adverse or unwanted operating conditions. Which IMO an uncontrolled line restriction is going to cause some type of pressure change somewhere in the system. I realize that refrigerant is a strange beast sometimes especailly in large quantities or in elaborate piping schemes where it changes state many times . But physical space is physical space and only so much any thing can fit in a predetermined space . Also I wanna say that I do NOT know it all ,I just think simple things should be kept simple. I am always willing to learn new things and feel like knowledge is the best tool any tech can have. Sorry if I sound"that way" I just feel like right is right and when there is an equation that does not have variables ,there should be none added for the sake of conversation.
Please don't take offense, but you need to study refrigeration theory some more.

Do you ever work on refer systems with receivers? The head pressure actually falls when that solenoid valve on the liquid line closes.

Do you work in the hvac field?

john.0522
09-18-2011, 10:13 PM
if the suction line is stopped up,(unlikely,but ya never know) the head pressure is still going to be high because it can't get thru the suction line
The head pressure is low because it canít get thru sum thing has to get thru for the compressor to pump itís not; the mass flow rate of refrigerant is decreased through the system.:cheers:

luskys a/c
09-18-2011, 11:03 PM
I am working on a ruud heat pump MN# upne-048jaz with an electric air handler inside mn#uhla-hm48 with R-22 coil mn#rcsa-hm4824au. The home owner called with a complaint of freezing up on hot days with 85 degrees and up. Unit is 4 years old and this is the first hot summer we have had since it's install (not an install of mine). With 80 degree ambient outdoor it has 180# head, 50# suction with 50 degree line temp. We sucked it down and purged with nitrogen and vacuum and weighed in a new charge. Checked the pressure drop across filter drier and all seems to be well there. Replaced txv and no change with that either. Have cycled unit into heat mode in hopes that if there was oil in distributor tubes when in heat mode i do have a slight pressure difference from each port. Any ideas?

You need to take basic steps before you go taking the refrigerant out and changing the TEV. Subcooling would have been the first route to take . 4 years old and no problems till this summer. You know that the ductwork is probably fine. Was the filter ok? Check the a-coil. I am assuming your standing pressure test passed before you continued on with your vacuum? Should have changed your filter drier since you opened the system up. If you tested your TEV then you would already know it wasn't it. Let us know what your subcooling is.

bob_scheel
09-18-2011, 11:11 PM
You need to take basic steps before you go taking the refrigerant out and changing the TEV. Subcooling would have been the first route to take . 4 years old and no problems till this summer. You know that the ductwork is probably fine. Was the filter ok? Check the a-coil. I am assuming your standing pressure test passed before you continued on with your vacuum? Should have changed your filter drier since you opened the system up. If you tested your TEV then you would already know it wasn't it. Let us know what your subcooling is.

Line temp 50 and pressure 50# is about 25 degree superheat. If subcooling is good then the problem is TXV or its adjustment. Assuming the measurements were made at the evap coil it doesn't look like an air flow problem. If low subcooling then its a low charge problem.

PalmettoMaintPro
09-19-2011, 08:30 AM
The head pressure is low because it canít get thru sum thing has to get thru for the compressor to pump itís not; the mass flow rate of refrigerant is decreased through the system.:cheers:

I know this sounds dumb but I thought about that same thing after my little rant up there. Makes sense though:yes:

Tommy1010
09-19-2011, 11:25 AM
It doesnt matter what the dry bulb is indoor or outdoor for the coil to freeze. As soon as you said 180 head and 50 suction, my first "guess" was low charge. 50 sat temp is 25-26 = below freezing.

Any moisture, humidity or condensate is gonna freeze on that coil. And unless the tstat satisfies and the fan stays in ON, its gonna keep freezing and spreading.

You head is also too low for an 80į day. I would like to see in the 230 - 260 range. But anything under 200psig for R22 head pressure, either theres an issue, or the darn thing shouldnt even be running.

But no ideas count with limited info giving. SH/SC is a must for this type of question.

Good Luck