high head pressure low suction - Page 3 - HVAC Site

RoBoTeq · 07-08-2009, 11:47 PM

Quote:

Originally Posted by mechanicalDvr

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.

mechanicalDvr · 07-09-2009, 01:08 AM

Quote:

Originally Posted by RoBoTeq

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.

hvactech · 07-10-2009, 12:36 AM

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?

I sure hope so after all that fuss!

bwalley · 07-10-2009, 10:28 AM

Quote:

Originally Posted by RoBoTeq

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.

RoBoTeq · 07-10-2009, 11:48 PM

Quote:

Originally Posted by bwalley

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.

Peal · 07-12-2009, 09:52 PM

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.

scooter · 07-13-2009, 12:40 AM

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!

Peal · 07-13-2009, 08:31 PM

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”

scooter · 07-14-2009, 11:35 PM

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

Peal · 07-15-2009, 01:25 AM

Quote:

Originally Posted by scooter

Sorry if I stuck a burr under your saddleblanket.
Scooter

If my replay was callused, I am sorry.

Quote:

Originally Posted by scooter

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:

Quote:

Originally Posted by tcbaker72

. 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.