Goodman Rooftop PHK024 High head pressure

[hockey]

I have an R22 Goodman Rooftop PHK024-1. Seems to work fine in cooling, but head pressure rises to above 400 psig in heating mode. I have to abort the defrost cycle because the head pressure rises higher than that. It is charged exactly (weighed in, checked twice). Any ideas? It's ~ 7 years old.

[skpkey9]

Check air flow ,make sure filters are clean.
Unit may be overcharged to compensate for an impacted evap coil.
Thats where I'd start.

[skpkey9]

By the way ...
What are the suction pressures in cooling and heating?

[hockey]

In heating mode: 90 psig; cooling mode: 50 psig. Sounds low, huh?

[Jabarco]

In heating mode: 90 psig; cooling mode: 50 psig. Sounds low, huh?


What is the external static pressure?

http://i199.photobucket.com/albums/aa214/jabarco/duct_p21.gif

[skpkey9]

Sounds like someone has some cleaning to do....:D :D :D

[hockey]

The airflow is good. This unit is sitting on the floor of a school with no ductwork. Let me now ask: to check a heat pump (hot gas method), the discharge temperature should be 126 degrees hotter than the ambient. If the ambient is 70 degrees, the measured temperature should be 70+126 = 196 degrees. This corresponds to a pressure of almost 600 psig. Doesn't this mean that the high head pressure is "normal"? I'm not used to 500 psig on any R22 system. I will measure the air temp in cooling and heating tonight.

[tatersalad]

where did you get the ambient plus 126 degrees? 600 psi....great googlie mooglie:eek:

[skpkey9]

Yeah if you want to know how long it takes to burn up a compressor:D
Evap coil is impacted and you system is overcharged. Like I posted earlier someone overcharged it to compensate for the impacted evap coil...

[Jabarco]

The airflow is good.

You really think so, huh? In the cooling mode the indoor coil is the evaporator and you have a low evaporator pressure (a sign of a low or restricted air flow).

Then when in the heating mode, the indoor coil becomes the condenser and you have a high condenser pressure...(another indication of a low or restricted air flow). So, why not just get your guages and check the pressures....the "external static pressures"..that is. Or, if for some reason, you can't find your gauge, open the unit and look at the indoor coil.

http://i199.photobucket.com/albums/aa214/jabarco/duct_p21.gif

Hey, I can't help it if you don't own a Magnehelic gauge!

[hockey]

There is no filter. The unit has no ducts. It is sitting on the floor in open space. It's never been outdoors! I can feel terrific airflow from the supply air. I got the 126 degree info from another Goodman heat pump document: CPLE24-1a (a split system). If a heat pump is supposed to supply 110 degree air at the register, and the refrigerant is 30 degrees hotter than that (140 degrees in the condenser), that is 337 psig.
Another post also states that the discharge line should be ~100 degrees hotter than ambient for a rough check.

[hockey]

I do have a magnahelic!

[skpkey9]

if I remember correctly the 100* above outside ambient pertains to goodman heatpumps only...

[hockey]

The unit is charged by weight. In fact, it's a 1/2 lb light!

[skpkey9]

Try to shine a flashlight through the evap.
If you cant ... impacted coil
and all over the coil not just one spot..

[hockey]

I'll buy the fact that if the indoor coil is clogged then the suction pressure will be low in cooling mode. But in heating mode, when the indoor coil is the condenser, if no air can get through the indoor coil, the head pressure should rise because it's not able to release its heat. I think that is what's happening. But shouldn't the outdor coil (now the evaporator in heating mode) have a higher pressure because the head pressure is higher?

[Jabarco]

I do have a magnahelic!

Hmmm, I don't remember seeing you at the HVAC Techincians Who Own A Magnehelic Convention last month. http://i199.photobucket.com/albums/aa214/jabarco/SanbarCroud.jpg

[heatingman]

There is no filter. The unit has no ducts. It is sitting on the floor in open space. It's never been outdoors! I can feel terrific airflow from the supply air. I got the 126 degree info from another Goodman heat pump document: CPLE24-1a (a split system). If a heat pump is supposed to supply 110 degree air at the register, and the refrigerant is 30 degrees hotter than that (140 degrees in the condenser), that is 337 psig.
Another post also states that the discharge line should be ~100 degrees hotter than ambient for a rough check.

If there is no filter, the inside coil becomes the filter. It needs to be cleaned.

100 degrees over ambient is a good benchmark. On any heat pump if you have no design data. 100 + 70 is 170 which puts you in the 400 lb range. I think part of the reason the pressure is high in heat, and the suction is low, is that there is no load at 70 degree incoming air, but the bigger issue is the coil being the air filter.

[hockey]

Hmmm, I don't remember seeing you at the HVAC Techincians Who Own A Magnehelic Convention last month. http://i199.photobucket.com/albums/aa214/jabarco/SanbarCroud.jpg

GET OFF MY BOAT!

[hockey]

Even though I feel great airflow, I will check the indoor coil and clean it. I'll let you know.

[Jabarco]

Even though I feel great airflow, I will check the indoor coil and clean it. I'll let you know.


Instead of using the beer can method to troubleshoot, get your Magnehelic on it and tell us the ESP!
http://i199.photobucket.com/albums/aa214/jabarco/duct_p21.gif

[mikelcs]

refrigerant restriction @ filter/drier or metering device?

[hockey]

We checked the metering device. MAYBE the drier is restricted...

[heatingman]

We checked the metering device. MAYBE the drier is restricted...

Take temp drop across the drier. If less than 2 degrees, its Ok. What kind of metering device do you have?

[vibration]

the discharge temperature should be 126 degrees hotter than the ambient. If the ambient is 70 degrees, the measured temperature should be 70+126 = 196 degrees. This corresponds to a pressure of almost 600 psig. Doesn't this mean that the high head pressure is "normal"? I'm not used to 500 psig on any R22 system. I will measure the air temp in cooling and heating tonight.
refrigerant from compressor is superheated, so dont use temp and T-P chart to find pressure.

[vibration]

There is no filter. The unit has no ducts. It is sitting on the floor in open space. It's never been outdoors! I can feel terrific airflow from the supply air.
check the supply and return air temp, if there is no duct there, maybe short cycle. check the evap coil if there is no filter.

[hockey]

You are correct: discharge is superheated so PT chart does not apply. I will check temperature drop/rise across indoor coil. It May be dirty!

[hockey]

I cleaned both coils (ID coil had a little dust). We found that the Goodman has two flow-check piston metering devices. ONe is 047 DIa, the other is .061 dia. Does anyone know what size they are supposed to be?

[raymoni]

I'm new here and thought i would respond to the known facts given. I do not think the coil is to blame.

1st problem- its a goodman.

2nd problem- heat pumps in heating are meant to run @ below 65 F. You are absorbing to much heat into the condenser coil assuming it is warm outside where you live.

3rd problem- you stated the AH is sitting on the floor with no ductwork-hence no static pressure or friction drop. the air is passing through the AH to fast and not able to reject the heat so your head pressure climbs.

4th problem- you state that in cooling you suction is low. again refer to #3, NO static pressure. air is moving pass the coil to fast and the coil is unable to absorb the proper heat in cooling. that is why the suction is running low.

This is how i see it with the info given and the fact that you live in MA and should be warm there.

to test the unit even with the above normal operating condition in heating. i would take a piece of card board and try adjusting air flow on the front side or return side of coil to try to get proper static. either use a magnehelic gauge or your gauges to get it in the ballpark.

[bamatech]

Why are you trying to run heat in middle of summer????????????
Like stated above you are trying to operate outside of design conditions.
If they need heat try bringing in some outside air that ought to do 'em...

[hockey]

Whoops! Sorry. We are a school. I am showing the students (and teachers) how a rooftop unit works. The room is 65 degrees. Surely that isn't too far out of heating spec.

[raymoni]

you are correct in the fact that 65 is not to warm, but it is pushing the design limits.

BUT the indoor temp is a bit unimportant. The outside temp is what matters sinse that is where the unit is absorbing heat to be rejected to the inside air. The warmer the outside air the more heat that the outside coil absorbs. once the refrigerant is compressed the indoor coil must reject the heat to the indoor air (heat pump in heating mode- medium air).

I think you are missing the MAJOR point. these types of units are disigned to be ran with DUCTWORK. The ductwork distributes the conditioned air into the space. A duct calculation is done off of the total cfm of the unit. the duct calculation takes into account- total length of run, friction loss, and proper cfm for return, and supply. This is what gives you the PROPER STATIC PRESSURE. This is to provide proper airspeed accross the coil.

with no ductwork your air is moving to fast accross the coil. The unit is absorbing alot of heat because the ambient is high.

with no ductwork on the unit the air is passing through the indoor coil to fast and the air unable to absorb enough heat (the heat that was introduced to the system from outside). if you ar not able to get rid of the heat at the indoor coil through airflow the pressure rises.....

[raymoni]

just a side note....when i said inside air is not important that is not waht i really meant. as long as the indoor air is cooler then the inside coil temp it is not a main issue. only if the indoor air temp was warmer then you would not be able to absorb heat into the air. you would actually be rejecting heat from the air to the coil.

the only other thing that i would mention ONCE you get the static pressure correct- is to ensure that the indoor fan is operating at proper speed and that when the unit was charged that is was charged properly and that there are no non condensables in the system. a quick way to check for non condensables, is to turn off the unit and hook your gauges up. wait for the unit to equalize. check your static pressures and ensure that they equal ambient temp. if the pressures are higher then the coresponding ambient then you have non condensables

[hockey]

Thanks for the added info. A heat pump becomes more efficient as the difference between indoor and outdoor temperature gets smaller. I have a case where a rooftop heat pump is in a room where the ID and OD temps are equal! The system is charged properly with no non-condensables. Readings are normal in cooling mode (supply is at 53 degrees and pressures are normal). In HEAT mode, the head pressure is above 400 psi (R22). But, the discharge line is approximately 120 degrees above saturated temp (normal for Goodman) and the supply air is 110 degrees (room is 65 degrees). This says the airflow and ESP is NOT the problem.
Original question: what is a normal head pressure in heating mode?
Newer question: what is the correct flowcheck piston sizes?
Once more: What is the normal head pressure in heating mode?