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Hvacrmedic is the guy who wrote what gravity mentioned.

Another trick is that when the unit has been overcharged the increased sc tends to help mask restrictions.

So the trick is kill the indoor fan and possibly recover some of charge and that will cause SC to drop which will cause more of a temp drop across suspect part.

there is a thread floating around here somewhere describing why you wont always have a temp split.

Originally Posted by gravity

i have a video of a drier i just found restricted. a carrier 28ton rtu. circuit #1 had pressures of 40/600. 600psi before the drier and 250 after the drier. this was a new microchannel coil. no temp split across drier but a pressure drop of 350psi! if i wouldnt have been able to check across that drier i would have said the condenser was restricted.

Wait? A pressure drop across the filter dryer didnt cause a temp drop? How is that possible? P/T relationship? Being that there is no load on that causing it to gain or lose heat just pressure drop should of cause temp difference? I had one last week that had a 50 degree drop across it, frosted on one side... Must be a rare one then.. Like to know on that, been a service guy for 2-3 years or so now residential and commercial RTU. Please enlighten me. Not saying your wrong at all, just want to learn more! LEARN EVERYDAY!

Originally Posted by beenthere

Old 8 and 10 SEER condensers could hold a lot og refrigerant. Micro channels can't hold nearly as much. Try pumping one down to itself.

I don't want to hijack this thread so I'll give up until this comes up in another thread.

Originally Posted by garyed

From what I've seen the microchannel units act no different than any tube & fin unit. They just hold less gas which makes them more sensitive to charge & they leak a lot. They probably hold the same amount of gas as an older 8 or 10 SEER might. I don't see how that would make that much of a difference. I've pumped down plenty of microchannel units before I ever knew I wasn't supposed to & they pumped down just fine. On long line sets I had to remove some gas first no different than I would any other type of unit. I'm not arguing that they can hold as much gas in the condenser as a regular unit but just that there was already less gas to compensate for in the system if the charge was correct so I don't see how that changes the basic principles.

Old 8 and 10 SEER condensers could hold a lot og refrigerant. Micro channels can't hold nearly as much. Try pumping one down to itself.

Originally Posted by beenthere

RTU and a split system are different, hen it comes to having a high head with a restricted LLFD. Microchannel condensers will have a high head as they just don't hold much volume, so there is no room for all the liquid refrigerant to stack up in them.

From what I've seen the microchannel units act no different than any tube & fin unit. They just hold less gas which makes them more sensitive to charge & they leak a lot. They probably hold the same amount of gas as an older 8 or 10 SEER might. I don't see how that would make that much of a difference. I've pumped down plenty of microchannel units before I ever knew I wasn't supposed to & they pumped down just fine. On long line sets I had to remove some gas first no different than I would any other type of unit. I'm not arguing that they can hold as much gas in the condenser as a regular unit but just that there was already less gas to compensate for in the system if the charge was correct so I don't see how that changes the basic principles.

Originally Posted by garyed

I 100% agree, we seem to have an argument about once a year about whether a liquid line restriction can cause elevated head pressure without the system being over charged. They obviously don't teach that in class so only those who have experienced it in the field can attest to it.

RTU and a split system are different, hen it comes to having a high head with a restricted LLFD. Microchannel condensers will have a high head as they just don't hold much volume, so there is no room for all the liquid refrigerant to stack up in them.

Our company has had a lot of 3 to 6 year old good man coils develop pin holes, Goodman rep called it formic corosion also said with r 410a so sensitive to moisture anytime the system is opened CUT out the dryer and replace it, never torch it out you would release any moisture it has trapped. Straight from the manufacturer on keeping the warrnty valid.

text book also teaches to take temp split across driers. i have seen only one drier in my lifetime that was dry on one side and sweating on the other. i have diagnosed all my other driers by taking a pressure difference across it.

Originally Posted by gravity

the unit was not overcharged. i weighed the tank when i recovered it and it was exactly what nameplate called for. only thing i can think is the suction piping and evaporator can hold more refrigerant then the microchannel condensor which is why it acted the way it did.

i have seen regular split systems with correct charge show low suction and low hi side pressure due to restricted llfd. i have also seen units overcharged with restricted llfd which shows low suction and really high hi side. each system is different. this is where experience takes over in the field

I 100% agree, we seem to have an argument about once a year about whether a liquid line restriction can cause elevated head pressure without the system being over charged. They obviously don't teach that in class so only those who have experienced it in the field can attest to it.

the unit was not overcharged. i weighed the tank when i recovered it and it was exactly what nameplate called for. only thing i can think is the suction piping and evaporator can hold more refrigerant then the microchannel condensor which is why it acted the way it did.

i have seen regular split systems with correct charge show low suction and low hi side pressure due to restricted llfd. i have also seen units overcharged with restricted llfd which shows low suction and really high hi side. each system is different. this is where experience takes over in the field

Originally Posted by gravity

i have a video of a drier i just found restricted. a carrier 28ton rtu. circuit #1 had pressures of 40/600. 600psi before the drier and 250 after the drier. this was a new microchannel coil. no temp split across drier but a pressure drop of 350psi! if i wouldnt have been able to check across that drier i would have said the condenser was restricted.

Was the unit over charged too?

Was told in school that every time the system is opened period you replace the drier, weather it had a leak or replacing any part that the refrigerant goes thru.


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Originally Posted by carmon

I have not and will not install the drier inside.... I see no point..... i like it outside so I dont have to braze in the customers home if repairs are required..... why do manufactures install them in the condensing unit now..... who is teaching this install the drier by the coil..... i dissagree

Inside the home is the last place I want to put a dryer.

It belongs outside at the condenser. I replace the dryer when I open the system.

i have a video of a drier i just found restricted. a carrier 28ton rtu. circuit #1 had pressures of 40/600. 600psi before the drier and 250 after the drier. this was a new microchannel coil. no temp split across drier but a pressure drop of 350psi! if i wouldnt have been able to check across that drier i would have said the condenser was restricted.

Just an update,after weighing everyones opinion and recomendations I pumped down the condenser leaving the original llfd and changed the evap coil.Normaly if there is a llfd outside the condenser I would have pumped down the unit removed the llfd and installed a new one at the new evaporator. Thanks for the input this is a good controversial subject like merv 6 filters vs the old fiberglass lol.

Do notget me wrong iam a advocate of replacing driers ,if i find a unit low charge due to a leak in evap coil and gas it up untill coil can be replaced if there is no indication of a problem with the drier i flat rate it for a pump down. If the drier is inside the unit it stays if it is in the liquid line it gets replaced and i do not add a 2nd drier. If i suspect the unit ran in a vacuum the drier gets replaced ,if it is in a vacuum i dont gas them up

Originally Posted by kangaroogod

How many times do you guys see a plugged/restricted drier? Honesty I Have never come across a ll drier plugged. It makes me wonder how many times I have missed it.

On residential maybe a couple times a year. Refrigeration much more often

Originally Posted by catmanacman

Replaceing a filter drier inside a unit that there is nothing wrong with is adding a expense that is not needed. On a evap coil replacement i pump the system down to about 25 close it off recover the rest .

How do you know there is nothing wrong with the LLFD. Its not like you added a access fitting to check for PD across it. Or know if it is at it saturation limit with moisture.

Originally Posted by kangaroogod

How many times do you guys see a plugged/restricted drier? Honesty I Have never come across a ll drier plugged. It makes me wonder how many times I have missed it.

Ran into a brand new Goodman Friday with a plugged drier. It took forever to diagnose cause you can't easily check the temp drops with it inside the unit. Sad thing is we had just uncrated and hooked it all up like 30 minutes earlier.