# Who is correct?



## hvac2010 (Jun 27, 2010)

I replaced a compresser on a 5 ton carrier roof top package A/C unit because of a burnout i put the charge in the unit but i cant get the super heat i need i could only get 43 degrees it says on the side of unit how much to put in which it says 7Lbs R-22 so i add more than the reqired amount until my head pressure is at 280 but the suction wont come up and the super heat is still at 43 which by that time i was a pound in a half over the reqired charge so i stop and look at the evaperator and see that it looks like the refrigerent is being restricted the evaperator has a distibution tube it was clogged somewere in thier in my mind so i tell the customer whats going on to see how far they want to go with this and they decide to get a second opion and that tech tells them that the evap is not being resricted but it just didnt have enough charge in it. I put 8.5 Lbs in it when i worked on it how could it be underchaged when calls for only 7lbs is Carrier wrong on the charge reqirement. Who is correct


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## DuMass (Jul 7, 2009)

As far as I know, the manufacturer’s nameplate data is usually quite accurate. 
Is your scale known to be working correctly or did you maybe add a cleanup filter on the suction side?
What was the amp reading at the compressor? That could help give you an indication as to whether it is working hard or hardly working.
Often the suction gauge pressure will drop when the comp is running if there is a severe liquid line restriction, similar to pump down.


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## hvac2010 (Jun 27, 2010)

My scales are brand new but i dont know for a fact that they are accurate. I did put a suction line filter on. The unit was pulling 24 amps and head pressure was running high. 300psi. Suction pressure was 60psi. The outside temp. was 95 degrees.


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## nicktech (Jun 22, 2009)

did ya get all the air out of the system? a non condensible like air will cause higher than normal discharge pressures. if carrier says 7lbs of r22, then thats that. is the txv sensing element installed properly?


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## hvac2010 (Jun 27, 2010)

I pulled the system below 500 microns and left it like that for 15min and the system is a captube style system. Can a system be pulled down to 500 microns and still have a small leak?


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## nicktech (Jun 22, 2009)

hvac2010 said:


> I pulled the system below 500 microns and left it like that for 15min and the system is a captube style system. Can a system be pulled down to 500 microns and still have a small leak?


it is possible, that a very small leak exist after all 500 microns has atmospheric pressure pushing down on it. Atmospheric pressure(15 psi) isnt much of a leak finder. hopefully you pressure tested it first with about 150 psi of nitrogen to leak check.


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## hvac2010 (Jun 27, 2010)

I pressure tested to 75psi but i will start testing it at 150psi from here on.


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## nicktech (Jun 22, 2009)

always refer to the data plate on the unit. it usually specifies150 low side test pressure value for r22 and 250 low side test pressure for r410a. but go with what the manufactorer recommends.


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## hvac2010 (Jun 27, 2010)

Thank you for the help next time I will know better.


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## ccc256 (Jul 31, 2010)

if you had a bad burnout debris from the compressor bbq got caught in the distributor tubes causing a restriction by adding more refrigerant you stack the condenser raising your head pressure this will compansate for the restiction but if it clears the head pressure will go sky high a good rule of thumb for any refrigerant is 100 110 condensing temp .195 psig for r22


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## hvac2010 (Jun 27, 2010)

I went back up on the roof and took a look at the unit to see what else the other contractor might have done and he also put a fan cycling control on and he had it set for the fan to come on at 300psi and to shut off around 280psi I diidnt get hook my gauges up because I wasnt thier to work on that unit again but the fan was running constantly so that tells me the head pressure has to be above 280psi.


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## ccc256 (Jul 31, 2010)

that unit will not last for very long.


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## hvac2010 (Jun 27, 2010)

I hope it lasts at least a year so i dont have to warrnty the compressor thats the 3rd compressor thats been put on that unit in 6 years that I know of.


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## ccc256 (Jul 31, 2010)

you should not be liable to replace compressor if it fails any company can get the waranty info thru the serial # there is a real problem in that unit .to many comp in a short time the problem could be simple or a real nightmare you info the customer with the problem and thats all you can do since he called another company looks like you don't need his business anyways theres no trust there but from what you say you have done all you can do at this point.


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## hvac2010 (Jun 27, 2010)

Thanks I will keep that in mind when that compressor takes a dump:shifty:


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## coolmen (Jun 4, 2009)

BURNOUT,
Do you still got some jnk in the system


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## hvac2010 (Jun 27, 2010)

I think thier is because the evap is restricted hine site I should have ran a system flush since it was the 3rd comp in 6 yrs.


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## artco (Oct 3, 2010)

Is there any obstruction in the return air such as a plugged grille. This will cause the low suction.
Are all the supplies open and have good air flow.

Was there a strainer in the original liquid line, this may be partially plugged.


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## hvac2010 (Jun 27, 2010)

The return air supply was in good shape and i replaced the liquid line filter as far as a strainer I diidnt see one their could have been one right before the evaperator orfices but i never got take the evaporater apart to see.


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## nH3man (Nov 3, 2010)

I recently had a carrier that had a burn out, I replaced the compressor and charged it up an the unit was doing the same thing. What I didnt notice was carrier installed these very small liquid dryers that unless you were looking for it would go unnoticed. My problem was easily noticable becuase it was almost completely stoped so it froze up right after it. This compressor was also replaced 2 or 3 times and all the techs before me missed it also. I just ripped out the liquid dryer the past tech put in and the small dryer that was factory was never removed. It was only about a 1/2 inch dia. and blended in well. Are your sure your not running into the same problem.


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## hvac2010 (Jun 27, 2010)

I dont know were was this filter located on the unit?


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## hvac2010 (Jun 27, 2010)

I dont know were did find this filter at on the unit?


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## nH3man (Nov 3, 2010)

It was located a short distance from where the liquid drain comes out of the condenser and goes to the evaporator. It was the smallest dryer I have ever seen and was completely stopped up.


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## hvac2010 (Jun 27, 2010)

Next time im on that job i will take a look at that thanks for your advise


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## nH3man (Nov 3, 2010)

No problem man, this carrier I was working on was a little older but techs before me that had changed the compressor and missed it and so did I. If it is in fact on there you are going to be completely shocked how small this thing is.


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## reese (Nov 18, 2010)

*Whos right*

Can't believe nobody asked what subcooling was? I realize it's a cap tube system but the subcooling will tell you if overcharged. It shouldnt be higher than about 15 degrees. Any higher its overcharged or restricttion.


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## costello (Dec 17, 2010)

I would say that the filter screen or dryer in front of the cap tube is clogged with carbon. I would have flushed or at least blown with nitrogen throught the suction line to reverse the flow to see what comes out. I had a unit that had a burn out that after i replaced the compressor i blew out system and installed new dryer on suction and liquid. The liquid dryer was clogged in 15 min. I replaced the dryer again and also found one infront of txv that is like the one the other guy described. After i replaced the dryer a second time it still got partially clogged again. This spring before they need cooling i have to go back and replace both dryers again. I would remove refrig and blow out lines and also install a filter dryer if had not done so before. Also the head pressure fan cycle switch should be set at 260 or so and cut off at 200 i would say. 

Thought if you do not have a filter dryer inline either factory or otherwise your cap tubes are clogged and they might need to be replaced or modify and put a txv on it instead.

just some thoughts'


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## repj2y (Dec 31, 2010)

*Agree with nh3man*

Check all U-bends for sweating to assure refrigerant feed.
Then; do a static pressure test with your manifold to see how fast your
system equalizes. If it doesn't equalize within 10 seconds -or- less, you;
need to remove the silica sieve drier in the liquid line -or- screen in front
of the distributor hub assembly. That restriction and probable oil
logging from subsequent compressor change-outs was definitely the
problem. "Been there" "Done that" ! Might happen again !

Gary Clemens
Another Air Conditioning Co. LLC
Ft Myers, Fl CAC027350


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## familyairman (Feb 24, 2011)

what are you talking about? fail to see anything about H.V.A.C. on this post at all>:blink:


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## familyairman (Feb 24, 2011)

Hi thats a major problem when you run on a job thats had multiple changeouts.just to cover yourself plus gain a customer for life,you really have to ck the system out for the true cause of the problem.Also need to go to the extremes of cleaning up the system so it doesnt attack your new compressor.I find in Az a big problem is system design.Lets face it air flow is a big factor on an effecient system.A duculator does help to ensure proper sizes esp in high seer makes.The next problem is system cleanup.How many people remove the accumulater and dump the nasty crap thats in there after a burnout! Youd be surprised the people that dont.If a burnout is very acidic you should go ahead and isolate the evap and condensor and clean seperately and definitly blow it out with nitro.Back in the day when freon was cheaper and there was no recovery laws it didnt take long to clean uop a system.Dont do that now fines are stiff so it does take longer to do.Package units are easier but split systems you do need to dial the freon charge in and take a superheat and subcooling test.If you truly understand this method those babys tell you whats going on with your system and it can be a very useful tool for you and excellent service for your customer by providing a effecient and economical running system.


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## familyairman (Feb 24, 2011)

Hi thats a major problem when you run on a job thats had multiple changeouts.just to cover yourself plus gain a customer for life,you really have to ck the system out for the true cause of the problem.Also need to go to the extremes of cleaning up the system so it doesnt attack your new compressor.I find in Az a big problem is system design.Lets face it air flow is a big factor on an effecient system.A duculator does help to ensure proper sizes esp in high seer makes.The next problem is system cleanup.How many people remove the accumulater and dump the nasty crap thats in there after a burnout! Youd be surprised the people that dont.If a burnout is very acidic you should go ahead and isolate the evap and condensor and clean seperately and definitly blow it out with nitro.Back in the day when freon was cheaper and there was no recovery laws it didnt take long to clean u:thumbsup a system.Dont do that now fines are stiff so it does take longer to do.Package units are easier but split systems you do need to dial the freon charge in and take a superheat and subcooling test.If you truly understand this method those babys tell you whats going on with your system and it can be a very useful tool for you and excellent service for your customer by providing a effecient and economical running system.


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## refermadness (Jun 23, 2011)

why would someone put a head pressure control on a unit that is already at 300 pds hp?


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## hvac2010 (Jun 27, 2010)

I asked them that and they told me it was because when it is cooler outside the temperature in the 70s the suction pressure drops down to low and thw unit looses more of its cooling capacity.


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## refermadness (Jun 23, 2011)

yes but at the time you didn't need it because your head pressure was already too high. Just like the dude who sold you that bill of goods.


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## refermadness (Jun 23, 2011)

sounds like you need to add a txv, doesnt matter this post is history


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## beenthere (May 30, 2009)

hvac2010 said:


> I asked them that and they told me it was because when it is cooler outside the temperature in the 70s the suction pressure drops down to low and thw unit looses more of its cooling capacity.



Thats when you should have told them that symptom is indicating a problem in the system. And the other contractor is only covering it up.


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## hvac2010 (Jun 27, 2010)

The one thing i have learnrd from this make sure you tell the customer that replacing a compressor that is shorted out dosnt garrentte that the unit will run write.


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## spinfisher (Nov 29, 2010)

Sounds like the owners have gone thru several tech and are still having problems, don't no how they are paying you but this might be one to walk away from. If you can't do a full system check then you're no better than the people before you. Wether that is your decision or the boss's, if this has been a prior burn-out (even multiple burn-outs) I would treated as a new install and start from scratch! Just my opinion!


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## hvac2010 (Jun 27, 2010)

Actually I did give them a quote for new system but they didnt want to spend that kind of money. How do you do a full sytems check if the compressor is already shorted out?


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## spinfisher (Nov 29, 2010)

You Don't!


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## superfittertech (Sep 22, 2011)

unless it's ancient that Carrier RTU doesn't have a cap tube it has multiple pistons in the evap header. more than likely one or more are plugged or the liquid line screen (it's not a dryer) is plugged up. The easiest way to tell is to remove the belt off the blower or disconnect power to the evaporator motor if it's direct drive and then run the compressor. You should have equal frost on all of the orifice tubes. The ones that are not are restricted or if the liq line screen is plugged it will have a temperature drop across it. If it's the orifices replace the whole evaporator. It's a real pain to replace the orifice tube header


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## superfittertech (Sep 22, 2011)

also reason other tech installed head pressure control is to raise the head pressure high enough to raise the suction pressure to prevent freeze up. Probably running about 300 or more head pressure


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## DirectComfort (Dec 9, 2011)

*A Super Heat and Sub Cool Reading*

A super heat and sub cool reading would have told you every thing that was wrong with the refrigerant side of the system. You can not properly diagnose a problem like this with out a sub cool reading. The sub cool reading would have told you if it was under charged, or it was a restriction.


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## hvac2010 (Jun 27, 2010)

Thank you for your advise. I will check the subcooling next time.


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## user2561 (Dec 29, 2011)

> I think thier is because the evap is restricted hine site I should have ran a system flush since it was the 3rd comp in 6 yrs.


This is the dead give away. Diagnose why the compressor has been replaced so many times. It is never good to simply replace the compressor....that is the symptom of a bigger problem. 

1)Check air flow for proper static pressure
2)Check that there are no "hidden" dryers that others techs may have installed or left behind.
3)Check the temperature of each capillary tube while in operation. They should all be relatively close. If one or more are way off..well, there's your answer.
4)If all of them are icing up and you are positive that the correct charge has been added and you have eliminated air flow issues and other possible causes...then the manifold for the cap tubes is the culprit.
5)If the unit is utilizing a compressor with manual service valves make sure they are not either broke or partially closed/opened.
6)Make sure the blower wheel is turning in the right direction.
7)Make sure the condenser fan prop or motor have not been incorrectly installed or sized by prior techs.
8)Depending on the ambient temperature during which the unit is cooling you do need a fan cycle switch however the setting you described would be incorrect. Most manufacturers will tell you what subcooling they are trying to achieve of the high side. The switch should be set accordingly. For example if this is a hair salon in a bustling mall or unit for a restaurant with a large heat load in the kitchen, they will be using cooling during the winter months. When ambient temperature get too cold and the equipment is trying to cool without a fan cycling switch the evaporator and metering device will ice up. The symptoms would be very similar to an undercharged situation even if the equipment was properly charged.


To help in properly troubleshooting it is very helpful to have dianostic sheet where you can add data and look at it collectively. This helps make sure that you are looking at all possible causes and allows you to have a comparitive look.


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