# high head pressure low suction



## tcbaker72

i am working on a trane condensor when I arrived at the job site I found the eveporator frozen solid. I thawed it out replaced the filters and cheked the coil it was fairly clean. I then found the pressure at around 45 psi on the suction and 185psi on the head. it was 90+ degrees out so I proceeded to add some refridgerant to the system and raised the head pressure to around 285 but could not get the suction above 50 psi. the superheat never fell below 18 degrees. I am thinking I have the wrong or missing piston or the compressor is not working properly. any ideas would help


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## JohnH1

Need to know the sub cooling but it sounds like you are stacking up refrigerant in the condenser and the orifice is plugged. You may be over charged now. If you were missing it you would be running a high suction not low. Are you sure it is not a TXV?
High head is normaly dirty condenser or substantilly over charged.


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## tcbaker72

ya its a piston not a txv but i think you are right about the over charge that is what concerned me and prompted me to post this.


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## supercool

even with piston type/ still need subcool, 
all trane systems have a check valve/ could be inop!
most trane systems never get cleaned very well cuz the panels are a pain! sounds like a double issue, john's right on it.


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## Yuri

1)I would wash the condensor. 

2)You don't know how much freon you have in now so you may want to remove it and weigh it back in with a scale. Lot less aggravation that way and then you have a good reference point to work with.


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## supercool

after you recover, flush system w/nitro - then after you calc. for lineset and factory charge, clean outdoor coil and watch as the head presure drops, if not suction will flutter and the check valve needs replaced!


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## JohnH1

supercool said:


> after you recover, flush system w/nitro - then after you calc. for lineset and factory charge, clean outdoor coil and watch as the head presure drops, if not suction will flutter and the check valve needs replaced!


Ok What check valve?:blink:


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## heatgain

It probably has a partial restriction and now you have overcharged it. I would start at the filter drier. Trane usually has a factory copper filter drier installed. Look for temp drop across it.


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## RoBoTeq

I agree with the filter/drier being a probable cause, but if you are still getting a solid line of liquid through the filter/drier, you may not be able to tell a difference in temperature. Your system subcooling will however tip you off to a partially blocked filter/drier.


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## mechanicalDvr

supercool said:


> even with piston type/ still need subcool,
> all trane systems have a check valve/ could be inop!
> most trane systems never get cleaned very well cuz the panels are a pain! sounds like a double issue, john's right on it.


 
I find it easier to pull the fan and spray in cleaner from the inside of a Trane condenser. You don't always have the room to pull off the outer panels.


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## scooter

Most Tranes dont get cleaned very well because of patented "Spine Fin " coils which are superior to Everyone elses coils because Blah Blah Blah.
tc if its over charged, who did it and why. 
Checking temp accros the filter is a great diagnostic tip but should be done in the first few minutes of running befor the whole line gets cold. with the numbers you put up it sure looks like a liquid line restriction but you are on the front line. 
back to basics. start fresh. Verify the complaint. listen to the customer!!!!!! he may tell you all you need to know.
I see it has been a few days? have you found anything yet?
Scooter


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## RoBoTeq

I believe I remember seeing posts about cleaning Trane/A-S spline fin coils using a blow torch. This is a public service post by someone who does not sell Trane or A-S:001_tongue:


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## mechanicalDvr

RoBoTeq said:


> I believe I remember seeing posts about cleaning Trane/A-S spline fin coils using a blow torch. This is a public service post by someone who does not sell Trane or A-S:001_tongue:


 
Lucky no HO tried it a blew his face off in the process, the lawsuit could have been real bad.


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## RoBoTeq

mechanicalDvr said:


> Lucky no HO tried it a blew his face off in the process, the lawsuit could have been real bad.


We could use a few incidences like that to keep HOs from buying direct from contractors selling on the Internet.


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## bwalley

tcbaker72 said:


> i am working on a trane condensor when I arrived at the job site I found the eveporator frozen solid. I thawed it out replaced the filters and cheked the coil it was fairly clean. I then found the pressure at around 45 psi on the suction and 185psi on the head. it was 90+ degrees out so I proceeded to add some refridgerant to the system and raised the head pressure to around 285 but could not get the suction above 50 psi. the superheat never fell below 18 degrees. I am thinking I have the wrong or missing piston or the compressor is not working properly. any ideas would help


I had the same problem on a 5 ton Trane package unit.

Non condensible's will cause this, pull the charge, remove and replace the drier, pull a vacuum to less than 450 Microns and make sure it holds, recharge the system and it should take care of the problem.


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## RoBoTeq

bwalley said:


> I had the same problem on a 5 ton Trane package unit.
> 
> Non condensible's will cause this, pull the charge, remove and replace the drier, pull a vacuum to less than 450 Microns and make sure it holds, recharge the system and it should take care of the problem.


And if the OEM filter/drier is on the inside of the unit, replace it with a piece of tubing and install a new filter/drier in the liquid line between the service valve and the indoor coil.


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## hvactech

I agree with the last 2 posts but what check valve are the others talking about? I have never seen a check valve in a split system or any other refer sys. unless 1 condenser serving multiple evaps.:blink:


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## bwalley

hvactech said:


> I agree with the last 2 posts but what check valve are the others talking about? I have never seen a check valve in a split system or any other refer sys. unless 1 condenser serving multiple evaps.:blink:


They are talking about the F.C.C.V.


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## RoBoTeq

hvactech said:


> I agree with the last 2 posts but what check valve are the others talking about? I have never seen a check valve in a split system or any other refer sys. unless 1 condenser serving multiple evaps.:blink:


 Carrier used to require a solenoid valve be installed in the liquid line close to the coil for bleed type TXV systems. Could this be what is being referred to?


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## bwalley

RoBoTeq said:


> Carrier used to require a solenoid valve be installed in the liquid line close to the coil for bleed type TXV systems. Could this be what is being referred to?


This is a Trane system that is being discussed.


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## beenthere

hvactech said:


> I agree with the last 2 posts but what check valve are the others talking about? I have never seen a check valve in a split system or any other refer sys. unless 1 condenser serving multiple evaps.:blink:


Trane uses check valves instead TXVs with built in checks.
A hold over from when they boought GE.

ICP also uses, or used check valves.

They are installed in a line the by passes the metering device when it switches to the opposite mode of what that metering device is for.


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## bwalley

beenthere said:


> Trane uses check valves instead TXVs with built in checks.
> A hold over from when they boought GE.
> 
> ICP also uses, or used check valves.
> 
> They are installed in a line the by passes the metering device when it switches to the opposite mode of what that metering device is for.


The Trane FCCV is the metering device.

On the 13 SEER and above they are not used, they now use a TXV.


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## RoBoTeq

bwalley said:


> This is a Trane system that is being discussed.


I understand that. Not ever having been a Trane dealer, I don't know that Trane did not do the same thing.


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## beenthere

bwalley said:


> The Trane FCCV is the metering device.
> 
> On the 13 SEER and above they are not used, they now use a TXV.


Talking about the older ones, that used seperate metering and checks.


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## RoBoTeq

beenthere said:


> Talking about the older ones, that used seperate metering and checks.


Ahhhhhh (the bell chimes)

You are talking about the bypass check valve that goes around a metering device when the coil is being used as a condenser.

Check valve goes bad and opens, oversized metering.......

.......would cause low head and high suction.


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## bwalley

RoBoTeq said:


> Ahhhhhh (the bell chimes)
> 
> You are talking about the bypass check valve that goes around a metering device when the coil is being used as a condenser.
> 
> Check valve goes bad and opens, oversized metering.......
> 
> .......would cause low head and high suction.


In this case the guy had high head pressure and low suction pressure, which leads me to believe it is non condensibles.


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## beenthere

RoBoTeq said:


> Ahhhhhh (the bell chimes)
> 
> You are talking about the bypass check valve that goes around a metering device when the coil is being used as a condenser.
> 
> Check valve goes bad and opens, oversized metering.......
> 
> .......would cause low head and high suction.


Ya, that be the one.

I didn't mean to imply that is what is wrong in this case.
just answering anotehr poster that never heard of it.


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## RoBoTeq

bwalley said:


> In this case the guy had high head pressure and low suction pressure, which leads me to believe it is non condensibles.


That is what I am figuring on as well, which is why I suggested emptying the system of refrigerant, changing out the filter/drier and evacuating to remove any and all non-condensibles. This would require the system to evacuate to below 500 microns but not below 250 microns and to hold below 1000 microns with the evac pump off.


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## RoBoTeq

beenthere said:


> Ya, that be the one.
> 
> I didn't mean to imply that is what is wrong in this case.
> just answering anotehr poster that never heard of it.


I understood that. I just was not getting where the check valve was located until you brought up the metering by-pass.


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## hvactech

the check valve must only be used on heat pumsp? and up here in MI we dont see too many heat pumps! my lack of experience in this really shows now LOL:laughing:


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## bwalley

hvactech said:


> the check valve must only be used on heat pumsp? and up here in MI we dont see too many heat pumps! my lack of experience in this really shows now LOL:laughing:


The FCCV are in Pre 13 SEER, straight cool systems,Trane and American Standard units as well.


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## RoBoTeq

bwalley said:


> The FCCV are in Pre 13 SEER, straight cool systems,Trane and American Standard units as well.


What does FCCV stand for? I assume the second C and V stand for Check Valve, but what does the FC stand for? What was the function of this check valve.


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## bwalley

RoBoTeq said:


> *What does FCCV stand for?* I assume the second C and V stand for Check Valve, but what does the FC stand for? What was the function of this check valve.


Flow Control Check Valve


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## RoBoTeq

bwalley said:


> Flow Control Check Valve


So this FCCV was actually the metering device? 

Sounds more like a fancy name for a piston.


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## bwalley

RoBoTeq said:


> So this FCCV was actually the metering device?
> 
> Sounds more like a fancy name for a piston.


Yes it is the metering device for the indoor coil, it does more than act as a fixed orifice metering device, that is why it is called an FCCV.


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## mechanicalDvr

hvactech said:


> the check valve must only be used on heat pumsp? and up here in MI we dont see too many heat pumps! my lack of experience in this really shows now LOL:laughing:


 
I have worked on thousands of heat pumps and haven't heard of that term "FCCV", it means nothing to me.


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## bwalley

mechanicalDvr said:


> I have worked on thousands of heat pumps and haven't heard of that term "FCCV", it means nothing to me.


Ever work on GE Weathertron, American Standard or Trane units?


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## mechanicalDvr

bwalley said:


> Ever work on GE Weathertron, American Standard or Trane units?


I have worked on many of them but most had TXVs. I go back to the old tan GEs with the controls in the top shell with the linset coming out the very bottom. I am close to 50 and have been doing this stuff since I was a kid in a family run business, where if you could walk you could work. I got a loaded toolbox for Christmas at 5 yrs old.


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## scooter

has any body heard from tc yet wether or not he found any thing?


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## RoBoTeq

bwalley said:


> Yes it is the metering device for the indoor coil, it does more than act as a fixed orifice metering device, that is why it is called an FCCV.


What else does it do? Is it electrically operated? Thermally? Does it change the metering somehow?


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## RoBoTeq

mechanicalDvr said:


> I have worked on many of them but most had TXVs. I go back to the old tan GEs with the controls in the top shell with the linset coming out the very bottom. I am close to 50 and have been doing this stuff since I was a kid in a family run business, where if you could walk you could work. I got a loaded toolbox for Christmas at 5 yrs old.


I never doubt some of the ways systems used to be operated. Those old GE heat pumps, as well as some Rheem/Ruud heat pumps, had air pressure switch controlled defrost controls in them.


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## mechanicalDvr

RoBoTeq said:


> I never doubt some of the ways systems used to be operated. Those old GE heat pumps, as well as some Rheem/Ruud heat pumps, had air pressure switch controlled defrost controls in them.


 
Oh man that is a blast from the past.


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## hvactech

Wow, 3 pages and the original question was never really answered, Or was it? Where the hell is TC and did he get the answer he was looking for? :laughing::yes::blink: I sure hope so after all that fuss!


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## bwalley

RoBoTeq said:


> What else does it do? Is it electrically operated? Thermally? Does it change the metering somehow?


No it is a mechanical (orifice) metering device in the cooling mode and when the unit is turned on in the heat pump mode, it allows the refrigereant to go around it, so it will not impeded the flow. 

I will see if I can dig one up and take a picture of it.


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## RoBoTeq

bwalley said:


> No it is a mechanical (orifice) metering device in the cooling mode and when the unit is turned on in the heat pump mode, it allows the refrigereant to go around it, so it will not impeded the flow.
> 
> I will see if I can dig one up and take a picture of it.


So it is a bypass only for a fixed orifice rather then for a TXV. That makes more sense. Must have been between fixed metering using cap tubes and sliding pistons that allow full bypass when slid in one direction.


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## Peal

I think bwalley is correct. 3 things will cause high head pressure; poor air flow across condenser, overcharge, or *non condensable* in system. Recover charge, check system for leaks, pull vacuum, and weigh in new charge.


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## scooter

too small a piston, too much airflow over evap coil, restriction in liquid line (filter/drier) condensor way below coil, condensor under a deck, condensor located in very hot envoiroment, there is alot more then three!


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## Peal

Scooter:
too small a piston, restriction in liquid line (filter/drier)

Ever put a unit into pump down. This is compete blockage of the liquid line. During pump down, no high discharge pressure. Besides if there is a partial restriction, the suction pressure will be low because the evaporator is being starved. Low suction pressure, low discharge pressure because of restriction. Unless overcharge, poor air flow across condenser, or non condensable in system. 

scooter
condensor located in very hot envoiroment

Are you talking about the unit having a higher discharge head pressure on a hot day compared to a cooler day? Sure, on hotter days the discharge pressure will be higher. But this is not abnormally high head pressures. These are normal head pressures associated with hot days. If the pressures are higher then the normal hot day pressures, then it is because of poor air flow across condenser, overcharge, or non condensable in system.

Scooter:
condensor under a deck

Poor air flow across the condenser.

scooter:
too much airflow over evap coil

I agree that the discharge pressure will be higher, along with a higher suction pressure. But tcbaker72’s opening statement was, *“**high head pressure low suction”*


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## scooter

TC is MIA
I am mearly trying to point out that all to often tunnel vision sets in and that there are no two systems that can be repaired with a cookie cutter repair. 
you are obviously convinced that there are non-condensables in the system, great, good advice, my point is that there are never X number of answers in such a dynamic industry.
what if the furnace/air handler fan is quiting, due to a relay or open winding, what if the blower wheel is so filthy or has a shoping bag stuck in it that its capacity is 1/2 what it should be. Unless TC answers these questions and any more that you throw his way then we are all just peeing in the wind without being able to see the system first hand.
Sorry if I stuck a burr under your saddleblanket.
Scooter


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## Peal

scooter said:


> Sorry if I stuck a burr under your saddleblanket.
> Scooter


If my replay was callused, I am sorry.


scooter said:


> what if the furnace/air handler fan is quiting, due to a relay or open winding, what if the blower wheel is so filthy or has a shoping bag stuck in it that its capacity is 1/2 what it should be.
> Scooter


Scooter, this is what I think. If the evaporator fan is not running for whatever reason, or if the squirrel cage capacity is reduced, then the evaporator heat absorption would be reduced. All of the liquid refrigerant would not be evaporated. Some of the liquid refrigerant would be returning to the compressor. This would show up as low suction pressure, one of the diagnoses reported, but there also would be low superheat.

This is what tcbaker72 said:



tcbaker72 said:


> . the superheat never fell below 18 degrees.


You are correct; there should be more information to make a better judgment call, but based on what he reported, I will stick with non condensables for now.


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## rico52177

tcbaker72 said:


> i am working on a trane condensor when I arrived at the job site I found the eveporator frozen solid. I thawed it out replaced the filters and cheked the coil it was fairly clean. I then found the pressure at around 45 psi on the suction and 185psi on the head. it was 90+ degrees out so I proceeded to add some refridgerant to the system and raised the head pressure to around 285 but could not get the suction above 50 psi. the superheat never fell below 18 degrees. I am thinking I have the wrong or missing piston or the compressor is not working properly. any ideas would help


 
If you add freon and the head pressure goes up but, not the suction...ou more than likely have a bad txv


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## chrisfrost

Also a semi-stuck reversing valve can restrict refr flow and to the previous poster that said that the refr is only metered in 1 direction would be a new 1 to me as I live and work in Phoenix where the heat pump is king and I've never seen a heat pump that was'nt metered both in cool and heat mode between evap and cond . Oops , I just noticed this is an old thread ,,,,,,


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## Residentialtech

Sounds like the txv is bad


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## MajorNelson

*High head*

I have an AmerStd with an accumulator. Works well in cooling but head goes straight up in heat. Low suction and I assume non cons but was wondering about the sizes of the new condensing coils vs evaporate coils?


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## beenthere

MajorNelson said:


> I have an AmerStd with an accumulator. Works well in cooling but head goes straight up in heat. Low suction and I assume non cons but was wondering about the sizes of the new condensing coils vs evaporate coils?


Sounds like a restriction at/in the outdoor metering device.


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