Low Head High Suction

[ayreon]

Neighbor asks me to check his a/c the other day ..
Last winter he had his other hvac buddy put in a furnace and A-Coil . He asks me to check it and that its not quite cooling the upstairs very well ..

Heres what i found:

Ambient temp 94%
Head pressure 190
Suction Pressure 90
Suction line temp 54
inside temp 75
wetbulb 69

So ive been thru this problem b4 with the low head high suction so i assume piston or a-coil . I open up the duct and the other hvac guy has put in a 3ton acoil . I told the neighbor that he should replace the acoil with a 2 1/2 ton .
He called his hvac buddy again to come look at it and apparently he told my neighbor that everything is ok and nothing needs to be done . Am i retarded or is 190 head on a 94% day a bit low :P

Any advice for me ? or am i completely wrong here ?

[tinknocker service tech]

inproper orfice or txv bulb in the wrong location

[pipedope]

the suction is to high. I agree wrong metering device.

[Jultzya]

You don't give condenser specifics, but if it's a 2.5 ton cond with a 3 ton evap coil... the 3 ton coil is NOT the problem!

So, what is the Make and Model of cond and evap?
I figure that it was a piston coil... since you didn't give the LL temp? (when diagnosing a system, you really should look at this too)

[lowtemp]

high suction and low head and high superheat. BAD suction valves in compressor

[BaldLoonie]

Many brands call for 3 ton evap on 2.5 ton condenser. Being a moonlighter install, is it a Janitrol/Goodman? I would suspect oversized piston too. What SEER is it? Head does sound low unless high SEER.

[Special Ed]

Originally posted by lowtemp
high suction and low head and high superheat. BAD suction valves in compressor


I agree. Let's keep it simple, guys. Often times it's the simplest solution that's the right one.

[rob10]

Bad valves.

[ayreon]

Well its a 2 1/2 ton Airquest and not sure of the a-coil brand at this time. I did pull the original piston on the coil and it was a 67 and the condensor called for a 65 so i did have one on the truck and replaced it but there was no change in pressures ! It is a 12 seer scroll compressor and it pumped down fine twice so i didnt suspect valves right away since it seemed to be working and pumping down without any leaking in the valves .. Something is wrong i know that much.. Let me know if u still think i should take action on the valves still after you've read this new info !! and thanks for the advice!

[jacob perkins]

Originally posted by ayreon
it pumped down fine twice so i didnt suspect valves right away since it seemed to be working and pumping down without any leaking in the valves .. Something is wrong i know that much.. Let me know if u still think i should take action on the valves still after you've read this new info !! and thanks for the advice!

This is a heat pump?What was the amp reading after the last "pumpdown"?

[Freezeking2000]

I would suspect the blower is running too fast, slow the blower and re-adjust the charge and see what happens.

[gbfromsd]

seems overcharged
Just finished a 12Seer this afternoon.
Startup per the charge chart was
190/70 at 75* ambient, suction approaching 80 for
90* ambient so your pressure arent completely whacko
but still off. Back off the charge to get 10* sh and
see what happens.

think about installing a TXV as a piston metered coil
has trouble with extreme ambients.

[hvac r us 2]

That does not look like bad valves to me at all. No way would you have a 54-degree suction line temp with bad valves.

Actually bad valves (with a fixed metering device) will give you low superheat, not high. Sounds crazy but true. Think about it, low compression, low head, high suction, and warm suction line…

Example, bad vales low head, high suction. Lets say 125-PSI suction, and a warm suction line lets say 72 degree suction line temp.

125 PSI R-22 saturated is about 72 degree’s (I don’t have a PT chart in front of me, got to be close though) minus 72 degree suction line temp is 0 degree superheat.

Why does that happen? Well, a compressor with bad valves becomes inefficient. Its pumping ability is less than designed which makes the fixed metering device oversized.

The trick is if the pumping ability is low there wont be enough refrigerant in the coil for all the heat that is passing over it. That translates into a warm suction line; cold suction line means more refrigerant that heat that can be absorbed by the refrigerant.

This job sounds to me like an oversized metering device. Head is low due to the inability to fill the liquid line, high suction and cold suction line from a flooded evaporator.

I would install a TXV,, IMO


[Edited by hvac r us 2 on 06-25-2005 at 09:53 PM]

[classical]

Bad valves in a Scroll yeah thats it!

[a\c don]

Originally posted by ayreon
Well its a 2 1/2 ton Airquest and not sure of the a-coil brand at this time. I did pull the original piston on the coil and it was a 67 and the condensor called for a 65 so i did have one on the truck and replaced it but there was no change in pressures ! It is a 12 seer scroll compressor and it pumped down fine twice so i didnt suspect valves right away since it seemed to be working and pumping down without any leaking in the valves .. Something is wrong i know that much.. Let me know if u still think i should take action on the valves still after you've read this new info !! and thanks for the advice!

If its a scroll compressor it doesnt have valves.

Maybe leaking internal bypass.

OOPs, that is a valve.:)

[tinknocker service tech]

to start off scrol compressors do not have valves. so i rule out bad valves. the orbiting disc i dont think can give you the same afect as valves will. could be to much air flo and over charge. stop playing arround and put in a txv and be done. i personaly feel a scrol compressor will preform better with a txv then a piston. you will get better mettering to the coil and you td might even drop
you will also pull out more humidity. 2.5 condenser,3 ton coil. what size is the blower.

[ayreon]

K, well i did check blower speed and it is on med for cool and ya i know thers no valves in scroll :P but it all the same concept ! Any way been the blower speed route already .. And i doubt the overcharge cause reclaimed and vaccumed then slowly charge while watching the pressures and they were off all the way if anything id say its a lil low since i stopped early on charging just to keep the suction from creeping over 90 when the suction was around 70ish the head was equallly low . Ya txv will be my next step i guess :P I thought i would see a differnce when i put the smaller piston in thinking id get my head up fill up the LL but nothing changed was quite disappointed after the fact! Well thanks for help i think ill stab a txv on her and go from there.

[tinknocker service tech]

stupid question here
did you check your gauges. i am only asking because one of my guys called me and said the unit he was working on wouldnt take the charge and he had low head. when i got there turned out even whit both knobs closed the high side was bleading through and giveing false readings
brand new man was he pissed

[ayreon]

Good question but yes i did put another gauge on it was the first thing i did cause i just replaced my highside a week earlier.. Grabbed my old set and it was the same :(

[dpatty]

Since you replaced the piston and the pressures remained the same I bet the piston is not sealing,maybe a defetive seat or some trash in there. Replace it with a txv and I bet the prob will go away. Be sure to blow it with nitrogen just in case it's trash.

[ayreon]

Well, stabbed in a txv this afternoon after work. And it works like a champ. Now i just got to write up the bill :P Thanks for the advice!

[binford]

That does not look like bad valves to me at all. No way would you have a 54-degree suction line temp with bad valves.

Actually bad valves (with a fixed metering device) will give you low superheat, not high. Sounds crazy but true. Think about it, low compression, low head, high suction, and warm suction line…

Example, bad vales low head, high suction. Lets say 125-PSI suction, and a warm suction line lets say 72 degree suction line temp.

125 PSI R-22 saturated is about 72 degree’s (I don’t have a PT chart in front of me, got to be close though) minus 72 degree suction line temp is 0 degree superheat.

Why does that happen? Well, a compressor with bad valves becomes inefficient. Its pumping ability is less than designed which makes the fixed metering device oversized.

The trick is if the pumping ability is low there wont be enough refrigerant in the coil for all the heat that is passing over it. That translates into a warm suction line; cold suction line means more refrigerant that heat that can be absorbed by the refrigerant.

This job sounds to me like an oversized metering device. Head is low due to the inability to fill the liquid line, high suction and cold suction line from a flooded evaporator.

I would install a TXV,, IMO


[Edited by hvac r us 2 on 06-25-2005 at 09:53 PM]

Ok so its an old post, but it was scary close to what I have.
( Google found it)
R22
Suction pressure 125, temp 75 ( 125=67° ) so 8° superheat.
Liquid line 215
outdoor temp 94
I figured it could be a bad compressor valve. Decide to just double check everything. its an Orifice vs TXV and the evaporator coil was clean enough.
I could feel the liquid line surging a bit too. Went back outside close the liquid line and watch the gauges. It started to drop like you would expect, but then started to slow down and would not drop below 55 psi and was holding steady. I open and the liquid line and pressures went back as noted above, re closed the still not dropping below 55. :gah:
The renter was not happy to say the least, I sure the owner won't be either.:deadhorse:

I like the new smiles

[Joker]

Ok so its an old post, but it was scary close to what I have.
( Google found it)
R22
Suction pressure 125, temp 75 ( 125=67° ) so 8° superheat.
Liquid line 215
outdoor temp 94
I figured it could be a bad compressor valve. Decide to just double check everything. its an Orifice vs TXV and the evaporator coil was clean enough.
I could feel the liquid line surging a bit too. Went back outside close the liquid line and watch the gauges. It started to drop like you would expect, but then started to slow down and would not drop below 55 psi and was holding steady. I open and the liquid line and pressures went back as noted above, re closed the still not dropping below 55. :gah:
The renter was not happy to say the least, I sure the owner won't be either.:deadhorse:

I like the new smiles

Looks about right to be a bad compressor. 125psig is about 73degrees F.

What was subcool?