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Discussion Starter · #1 ·
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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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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Discussion Starter · #3 ·
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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Energy mover
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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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Discussion Starter · #5 ·
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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Energy mover
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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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Energy mover
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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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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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Discussion Starter · #11 ·
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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Discussion Starter · #13 ·
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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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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Discussion Starter · #17 ·
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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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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Discussion Starter · #19 ·
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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Mechanical Contractor
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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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