AC Liquid line very hot

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  #1  
Old 06-02-08, 07:41 PM
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AC Liquid line very hot

My ac unit is not working very well, so I cleaned the evaporator and condensor, but it didn't improve. I called the service guy and they checked it out and concluded that I need a whole new condensor (outside unit).

The problem is, he measured 80PSI on the suction line and 300PSI (34deg above ambient) on the liquid line and he said the system was likely plugged resulting in the high pressure. He measured the compressor current and it was 14.3A while its rating is 14.8FLA and concluded that it was the compressor. What I have a hard time understanding is why the compressor would develop too much pressure if it was on its way out. I would hate to pay $2800 for a new condensor only to find out that the line is plugged somewhere inside the house. Is it more likely that I have an obstruction elsewhere in the system? If the consensor/compressor is on the way out, or has an obstruction, then does it make sense that he would measure 300PSI on the liquid line?

Any advise would be appreciated so that I can make the right decision.
 
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  #2  
Old 06-03-08, 04:02 AM
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I have some questions/comments...
1- Could you tell us how did you clean the coils? For the outdoor unit a wetting of the coil should be done, followed by spraying a special solution (chemical) that foams out the dirt, followed by pressure washing. You clean the outside of the outdoor coil. A different solution is needed for the indoor coil (which is usually difficult to access, if at all) and here it is cleaned from the furnace side. Watering with a garden hose is not enough.
2- Did the tech check for a possible refrigerant overcharge? Yes, the pressures are on the high side. But this could be caused by a few things other than ... a plug in the lines??? (1st time I hear of something like that)... examples of things that would bring the pressures up: dirty condenser coil, defective condenser fan motor (not spinning at the rpm it should, or is an undersized replacement), overcharge of refrigerant, excessive evaporator load (is this unit attic mounted?)
3- how's the layout of the outdoor and indoor units? outdoor unit on a backyard (or roof?) & indoor in a basement (or attic?) I'm interested in getting a mental picture of how the refrigerant lines between the two units run.
4- the compressor is not running overloaded (its running amps are still below the nameplate amps, which is good), but its amps sure are on the high side.
5- Bear in mind that higher pressures mean higher refrigerant temperatures. A common mistake is to think that the more refrigerant you have in your system, the more cooling you'll get. Exactly the opposite happens with an overcharge of refrigerant. Was your unit recently serviced and refrigerant added?
6- Pls post the MFR and full M/N of both, the outdoor as well as the indoor units. Hopefully some tech lit from the mfr is available online that may help
 

Last edited by pflor; 06-03-08 at 06:17 AM.
  #3  
Old 06-03-08, 07:43 AM
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Thanks for your reply.

Firstly, I purchased the house a few months ago, so I have no history on the unit. This is the first time I have turned it on and the first time I have given it attention. To answer your questions:

1) I cleaned the condensor coils with compressed air by blowing from the inside after I pulled the fan off the top. They were dirty, but I thought I cleaned them quite well. Perhaps a better cleaning is in order. I had easy access to the evaporator coils, that was behind a cover and I blew compressed air from the furnace side and vacuumed from the filter side. These coils do not look to dirty and there seems to be plenty of airflow. With the unit running, the evaporator coils don't seem to be getting very cold and don't freeze up.

2) I asked about a refrigerant overcharge, but he said that could not be the problem. Not being an AC guy, I didn't know what he could do to test for that. Is there something he could have done?

He measured the fan motor current and said it was ok and it appeared to be spinning well. The air coming off the fan seems very hot, but there is plenty of flow. Probably about 30 degF above ambient. At the condensor, the suction line was about 80 and the liquid line was about 130 meanwhile the outside temp was 96 and the inside (air intake temp was 98).

3) The Condensor is mounted outside on the ground next to the house, the lines run in the crawl space to a closet about 15ft away and into the inside unit. The inside unit has an air intake plenum with the evaporator mounted on top, the fan above that and an electric heater on top. The inside unit is mounted in a closet and at the very top, the plenum goes off into the attic. The unit is an intertherm, but I will have to check the model numbers when I get home tonight. It's a 3T unit.
 
  #4  
Old 06-03-08, 08:22 AM
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Originally Posted by steve-1 View Post
Firstly, I purchased the house a few months ago, so I have no history on the unit. This is the first time I have turned it on and the first time I have given it attention.
That home inspector you hired sure did a lousy job!

Originally Posted by steve-1 View Post
1) I cleaned the condensor coils with compressed air by blowing from the inside after I pulled the fan off the top. They were dirty, but I thought I cleaned them quite well. Perhaps a better cleaning is in order.
You need the chemical. Also, beware of not bending the aluminum fins. If with the air compressor you flattened some and air cannot go through, that could very well be the reason for the high pressures you are reporting...now you will need to comb the fins...you should be able to see thru. And compressed-air won't take the dirt attached to the metal parts, just the superficial dust.
Originally Posted by steve-1 View Post
I had easy access to the evaporator coils, that was behind a cover and I blew compressed air from the furnace side and vacuumed from the filter side.
Now I'm getting really worried. compressed-air is most definitely NOT the way to go.
Originally Posted by steve-1 View Post
These coils do not look to dirty and there seems to be plenty of airflow. With the unit running, the evaporator coils don't seem to be getting very cold and don't freeze up.
Indeed. It is the outdoor coil the one that (for the most part) gets the blunt of the dirt. It's good the indoor coil don't freeze up, but not good that it doesn't get cold either. And it won't get cold with a pressure of 80psig...that baby should go down to about 70 "tops"
Originally Posted by steve-1 View Post
2) I asked about a refrigerant overcharge, but he said that could not be the problem. Not being an AC guy, I didn't know what he could do to test for that. Is there something he could have done?
Oh boy, oh boy!!!! How can a service "professional" read the high pressures you report and flat-out discard an overcharge as a possibility? the guy is (a) a rookie, or (b) lazy. One cannot just toss out that possibility without taking the time to test things out. Anything you can do? I'm afraid not...you need special tools/testers and to tap into refrigerant lines you need a federal certification, else you'd be breaking the law. It looks like you may have messed-up some of the fins with the compressed air (let's hope that's all it is)
Originally Posted by steve-1 View Post
He measured the fan motor current and said it was ok and it appeared to be spinning well. The air coming off the fan seems very hot, but there is plenty of flow. Probably about 30 degF above ambient.
All these are quite normal
Originally Posted by steve-1 View Post
At the condensor, the suction line was about 80 and the liquid line was about 130 meanwhile the outside temp was 96 and the inside (air intake temp was 98).
96 in early June??? Very hot, huh? Do you live in venus or something? Pls tell which type of expansion device your indoor coil has: TXV or piston? and which type of refrigerant: 22 or 410A?
Originally Posted by steve-1 View Post
3) The Condensor is mounted outside on the ground next to the house, the lines run in the crawl space to a closet about 15ft away and into the inside unit. The inside unit has an air intake plenum with the evaporator mounted on top, the fan above that and an electric heater on top. The inside unit is mounted in a closet and at the very top, the plenum goes off into the attic. The unit is an intertherm, but I will have to check the model numbers when I get home tonight. It's a 3T unit.
Call me crazy, but I have to ask: is it even remotely possible that the strip heater on top of the coil is messing things up by staying engaged?

Also, and again just playing devils advocate, maybe (just maybe) your unit is on the "undersized end". Have a heating/cooling load calculation professionally done to make sure that is not the case.
 
  #5  
Old 06-03-08, 07:38 PM
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I am confident that I did not bend any of the fins when cleaning out the evaporator or condensor. I likely did not clean the condensor very well, but I am sure I did not make things any worse.

I bought a couple of cans of cleaner and will wash out the condensor with the chemical and water this weekend. I will need to call the company back (or get someone else) if the cleaning does not work, but what should I ask them to do? Should I have them empty the system and re-charge it with new refrigerant?

The evaporator and condensor are made by Nordyne, I don't have the model numbers handy. I'm not sure what type of refrigerant or system it is. I will get model numbers this weekend and hopefully you can tell from that.

I'm in central Texas and yes, it's hot!! I have checked out the heater and I'm sure it is off and the unit is a 3T for a 1200sqft manufactured home. I think that's about right for our location.
 
  #6  
Old 06-03-08, 08:11 PM
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Take the cans of cleaner back

Find an A/C supply house in your are and buy a "Coil Gun" made by NuCalgon. Also buy a gallon of foam brite condenser coil cleaner. Disregaurd the mixing directions of the foam brite and follow the coil gun directions.

You are supposed to clean the coil from the inside out but the compressor does get in the way. So do it both ways.

Wet the coil first as pflor said. Wash with coil gun on low (E) setting and watch the dirt foam out. Rinse and reaply. Rince and try it our. You will see a difference.

Also find a new service company.
 
  #7  
Old 06-04-08, 03:53 AM
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very good advice, JD...short 'n sweet - and to the point
Steve, follow the directions given, you'd be o.k.
 
  #8  
Old 06-07-08, 07:52 PM
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So I followed your advise and cleaned the condensor with a NuCalgon coil gun and foam brite. I also cleaned the evaporator with a NuCalgon evaporator cleaner spray can. The condensor was very dirty so I cleaned it twice to make sure it was totally clear.

Overall, it seems to cool a little better, but the liquid line is still much hotter than the ambient and the suction line is barely cool to the touch (perhaps 75deg) at the compressor. Below is all the information on the unit that I could get:

Condensor:
Mfr: Nordyne
Model: S3QA-36KA 3Ton
Compressor Mode: MR
Factory Charge: R22 (oz): 69
Design Pressure (PSIG): 400 High, 150 Low

Evaporator:
Nordyne 911969
I don't know what type of condensor this is (TXV or piston)

What do you recommend I do next? Should I call a different ac company and ask them remove the refrigerant and re-charge it to the correct specs? Given the design pressure indicated on the condesnsor, do the numbers in my earlier post make sense or are these maximum pressures? I don't want to replace the whole condensor unless you guys tell me that there is nothing else to try.

Thanks for your help!
Steve.
 
  #9  
Old 06-08-08, 08:00 AM
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I'll be out most of the rest of the day, I apologize for not being able to help with as thorough an explanation as I would like to.

But bottom line is yes, I believe that good chances are that an overcharge may be causing this spike in operating pressures. There may be other factors as well, unrelated to a refrigerant charge that may be worth talking about.

I'll try getting back in touch 2nite, unless of course someone else gives you a hand in the meantime and takes care of your Q's.
 
  #10  
Old 06-09-08, 06:53 AM
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I will wait for your next response before I call someone out to look at it.

One other experiment I ran was to disable the blower fan inside and run the ac for 5 minutes. When I did that, the liquid line ran much cooler and the suction line at the condensor cooled right down and water started condensing on it like I would have expected. Does this provide any telling information?

Something else to note is that when the unit turns off, I hear some noise in the lines at the evaporator as the pressure is bleeding off and there is a bubbling sound. The liquid line then cools off rapidly to room temperature.

Thanks again,
Steve.
 

Last edited by steve-1; 06-09-08 at 07:51 AM.
  #11  
Old 06-09-08, 08:26 AM
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Originally Posted by steve-1 View Post
One other experiment I ran was to disable the blower fan inside and run the ac for 5 minutes. When I did that, the liquid line ran much cooler and the suction line at the condensor cooled right down and water started condensing on it like I would have expected. Does this provide any telling information?
Indeed. The indoor blower moves house air through the cold coil (evaporator). Inside this coil there is refrigerant...the refrigerant is cold (say, about 40F), absorbs the heat from the air (say, about 75-80F), cooling the air off (to about 55F)...and b/c it absorbs this heat, the refrigerant turns into gas (boils). If the blower is turned OFF, no more warm air comes in contact with the coil...no more heat is transferred to the refrigerant...the refrigerant no longer boils...pressures drop and temperatures (inside the pipes) do so as well. That is why the liquid line does not feel that hot anymore.


Originally Posted by steve-1 View Post
Something else to note is that when the unit turns off, I hear some noise in the lines, there is a bubbling sound.
Most certainly normal. Say you're riding in your car at cruise speed. Put the transmission on Neutral and turn the ignition OFF. The car will slow down progressively and will move some distance before coming to a halt. So is with the refrigerant...the engine is the compressor, it keeps the refrigerant moving (that's the bubbling sound you hear, refrigerant moving and boiling as it picks-up heat from the house air). If you turn the thermostat OFF, the bubbling continues for a few seconds and then stops. If you keep the t-stat ON but turn the indoor fan OFF, the bubbling will diminish in intensity (at some point you may not even be able to hear it).

Back to your problem: It is normal for the liquid line to be hot...or should I better say: "warm". A normal temperature would be around 90-to-100F. But if there was a problem (such as an overcharge, a defective outdoor blower, a very dirty outdoor coil, etc.), pressure inside the lines will be higher than normal, and as pressures get higher the temperature of the refrigerant inside gets higher as well.

You cleaned the coils - so this is no longer a possible source of trouble. Let's assume the outdoor blower is in good condition and doing its job, if so it is not the source of your trouble either. What does that leaves us with? a likely overcharge.

Say an hourly worker: the higher the number of hours worked, the higher the amount of money in the paycheck
As for the refrigerant: the higher the operating pressures, the higher the temperature of the refrigerant inside. When it comes to refrigerants, Pressures and Temperatures ride together. Both up, or both down. If your system pressures are higher than normal, the refrigerant temperatures will be higher than normal as well (or, say: not as cold). You then feel your unit is not cooling as much.

But the trouble could also be an undersized system...too small a unit for your house. Though this is very unlikely as contractors usually go thru great pains in oversizing anything they install . has this problem happened before? If there is a history of this unit not cooling off well when is steamy hot outside but does a fine job anytime else, then an undersized system is something to ponder about.


Hope this helps.
YES, have your unit checked for a possible overcharge.
 
  #12  
Old 06-09-08, 01:21 PM
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some of the older Nordyne units ran higher pressures than you would normally see on newer units. 300 on high side and 80 on low would not be that unusaul if the inside ambient return air temp was in the high 80's and 90's especially with a fixed orfice sytem. A real technician will take superheat and subcooling measurements to determine what the real problem is. I think you need a BETTER tech on this. Actually it is probably beyond a lot of so called techs ability to do proper diagnosis LOL you will have to screen your guy a bit to get someone to help you properly. I doubt that you have a compressor problem with those pressures. We really need to know a lot more info on pressures and line temps ambient inside/outside temps and wet bulb temps etc. to do a proper diagnosis. Get yourself a competent type tech and GIT UR DUN. If the guy needs some help send him our way we will straighten him out if he has proper equipment.
 
  #13  
Old 06-09-08, 03:08 PM
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Hey now Saturn.

This is DIY for homeowners, not DIT School for Techs who "should" know this stuff already.
 
  #14  
Old 06-09-08, 06:57 PM
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I agree with you guys that the tech did not know what he was doing which is why I posted here. This is the second time I have run into this, but anyway here are the numbers he recorded (before my proper cleaning of the condensor). Not sure what everything means but here it is:

A/B 96/130
80/300
Scool=11
Sheat=36
Inside Intake 98
78/98 =11 TD
Liquid temp=119

The house is about 1200sq ft. I provided the unit model info above. I plan on trying with yet another company and I will start out by asking them to check for an overcharge and request that they remove the freon and re-charge it to spec.
 
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Old 06-09-08, 07:21 PM
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I'm not sure what the A/B 96/130 is all about

But I see an intake of ...98F ?????
Was the inside of your house at almost 100F when the tech was taking those readings???
If so, that explains the high pressure readings and higher than normal liquid line temperature.

FYI, readings should be taken after the unit has been running for a good 20 (or more) minutes, and the house has had the opportunity to cool down and go through a cycle or two...but never as soon as the system is just turned ON. In addition to what you show below, the tech should have taken EWT and OT (Entering Wet Bulb as well as the Outdoor Temperatures)

IF the system is indeed overcharged, all they have to do is use a recovery machine to remove the "excess" refrigerant so the charge goes down to specs...the unit does not need to be recharged.
 
  #16  
Old 06-09-08, 07:44 PM
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Thanks, I'll call someone else in. It was hot, but had run for about 20minutes. Running continuously it gets down to about 80deg though.
 
  #17  
Old 06-09-08, 07:46 PM
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Agree with the A/B thing, but 131 is sat temp for 300 psi.

98 return temp.

11 across coil

11 subcool. 36 superheat.

Turn it on when the sun goes down and let it run.

Tech has to let it run, why pay him/her to wait.
 
  #18  
Old 09-27-08, 09:29 PM
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I have been suffering with poor ac all summer .
After calling out two more ac techs and forking out hundreds to have them clean, re-clean and recharge the system I finally found the problem myself.

The plenum above the ac unit in the attic had several split seams and was blowing cold air into the attic. I figured this out by cracking a window and turning the ac fan on and off. Each time it ran there was a significant draft into the house, because air was escaping into the attic. The repair was a big job since I had no attic access. I opened up the ceiling and sealed the plenum with aluminum tape and mastic cement. Now it works great and when cracking the window there is no draft with the fan running.

I thought I would post this so that some ac pros would at least consider this when checking a system. I'll bet this has occurred before and wish that some of the techs who checked out my system would look at the whole picture. I'm a do it yourselfer and appreciate the help you guys have given me, but feel misled by the techs who came out to my home. Hopefully sharing this information will make a difference.
 
  #19  
Old 09-28-08, 07:36 AM
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the compressor doesn't produce high head the condenser produces the high head read on a guage when it isn't pulling the heat out of the gas your feeling on that liquid line.a clean condenser will raise the discharge air temp.out the top 10F from the ambient going in as the condensers gets dirty the heat will start to show up on that LL as you felt.with no access into the attic i take it the filter is in the return grill in the hall or attic ceiling.if your still open there......check the rounds on the squirrel cage on that air handler.there are big bucks in changing condensers out if you can count how many times in the past years has somebody put a set of guages on that condenser?if they didn't purge the suction line(blue hose) onto the insulated line they pushed air into the system.then on a hot day that air will give you high head because the air is considered a non-condensible and takes up space within the condenser cutting down the area and results in high head readings.normal running head presurres should be 30F above the entering air...so the pressure shown should corresspond with the inner temp ring on the discharge guage.
 

Last edited by sminker; 09-28-08 at 07:58 AM.
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