Hvac/r

[tswiczko]

Got a question I had been a service tech for about 15 years. my S.I.L. asked me to look at her A/C the other day because she has someone coming to replace the compressor. He says it's worn out.

complaint is, It does not keep up and runs constantly.

I don't think it is the compressor. What do you guys think?
installed 1993
2.5 ton
fixed orifice
both coils are clean and in good shape
amp 6.5 of 9 fla
head 200psi. out door temp87*f
suction 100psi.
in door temp 77*f
temp split across the coil 13*f
super heat is 8*f

when I pulled my low side manifold line off, there was liquid (mist) not oil.
compressor sounds quiet,(not rattly) and sweating on can
no one has put any refrigerant in it to cause an overcharge.

I suspect the piston is stuck or the seal on the end of the piston is damaged.
causing the flooding back and causing the low head and high suction and flooding back.

it has been my eaxperience that a worn out compressor causes a higher than normal amp draw and doesn't cause flooding back.

 

[mike243]

Re: Hvac/r

is it a heat pump? ,

 

[mike243]

Re: Hvac/r

a dirty restricked evap with cause the suction to be high & a no cool condition,clean the evap even if it dosent look dirty & make sure fan is running,

 

[tswiczko]

Re: Hvac/r

is it a heat pump? ,

Not a heat pump

A lack of air flow would cause a low pressure ot the return side and freezing on the evaporator

I am seeing a low side pressure of 100+

This is an R-22 system

 

[SS MAYFLOAT]

Re: Hvac/r

I would say something is worn on the inside the compressor. More than likely the valves not seating causing leakage. The low amp draw tells me the compressor is having an issue with building pressure on the high side. Sorta like taking a spark plug out of your lawn mower engine that makes it real easy to pull vs a bit more harder to pull with the plug in.

With the unit being that old, I would tend to think of a whole new more efficient condesner unit with a complete warranty.

 

[tswiczko]

Re: Hvac/r

Thats what I thought SS but I don't think it would be flooding back, Would it?
( I blew through the A coil with Co2 and nothing came out so I'm pretty sure it is clean)

 

[SS MAYFLOAT]

Re: Hvac/r

Your liquid is coming back through the bad valves from the high side within the compressor. It doesn't mean that you are getting flood back from the "A" coil.

 

[hrdwrkingacguy]

Re: Hvac/r

Lower then normal high side pressure(at 87degrees should be 245#-260#ish) and higher then normal low side pressure(at 77 degree indoor and guestimate wetbulb temp of 62ish pressure should 65-69#ish) That condition is always classified as a internal bypass weather it be reversing valve(which you don't have) or bad compressor valve, or somewhere else in the system like a check valve(that you also don't have)...

If everything was normal and all of the sudden you have high low side pressure and low high side pressure you have a bad compressor...The way to check it is with gauges on close the liquid line service valve and run it, pump it down to like 10psi low side and watch if the pressure rises and you can hear hissing...

PS a "worn out" compressor that doesn't pump causes lower amp draw because it isn't doing any work...Compression ratio determines amp draw and when you have the pressure you do the ratio is low and amp draw goes with it...

You have low amp draw and pressure indicating, bad compressor valves...Make sure whoever fixes it owns a micron gauge and removes all the driers and strainers in the system...

One other thing...If by fixed orifice you mean a piston(not cap tube) the piston being wrong size or the unit being mismatched could cause that same situation...

 

[tswiczko]

Re: Hvac/r

Isn't that kinda like water flowing uphill ?

 

[hrdwrkingacguy]

Re: Hvac/r

a dirty restricked evap with cause the suction to be high & a no cool condition,clean the evap even if it dosent look dirty & make sure fan is running,

Not trying to start a war but this is only true in the heat mode...Lack of heat transfer(meaning dirty filter,dirty coil, panel door off, bad motor) in the cooling mode causes low pressures, low superheat,low sub-cooling, and freezing condition...

In heat its a different story because it is essentially the condenser coil it is the complete opposite high pressures, high sub-cooling, overheated compressor...

 

[tswiczko]

Re: Hvac/r

Ran O.K. for 17 years. I haven't tried a pumpdown, I will try one this weekend if they don't have the compressor replaced by then.

what do you think about the super heat?

I expected if it were weak or bad valves it would be up aroud 20* or more

 

[hrdwrkingacguy]

Re: Hvac/r

100# = 67 degrees...6 degrees of superheat means your suction line is 73...Your house is 77 degrees...Superheat is irrelevant at that point...Your suction line is 4 degrees warmer then your indoor temp...Normally if a system is running 68# = 40degrees and the suction line is 52 on a txv...The room is 78...26degree difference between the suction line and the indoor temp...Heat moves from a hotter place to a colder place...bigger the difference the more efficient the transfer is...

Readers digest abridged version = your unit is screwed...

 

[mike243]

Re: Hvac/r

shut the high side valve & pump it down till it bottoms out,pull the power off it & see if the pressure equalizes,depending on the lenght of the lineset it can hold all of it in the condenser more than likely,no war here,a lot of times the basics mess folks up,mike243

 

[tswiczko]

Re: Hvac/r

Thanx for the input guys

the guy didn't show up today so I went over there this evening

I did a pump down and it held so I went to the storage unit and found a TXV I had stashed and replaced the piston and lo and behold the head pressure returned to normal and they have a 19*f delta T on the "A" coil

I haven't done any refrigeration since my wreck in 06

totally forgot about pumping it down to check the valves

my SIL is happier now that she doesn't have to pay for a compressor

 

[hrdwrkingacguy]

Re: Hvac/r

As long as you have 8ish degrees sub-cooling and a suction line in the high 40's low 50's you are golden...

 

[tswiczko]

Re: Hvac/r

Thanks A/C guy I appreciate it Lo side Pressure 66# to 70# it hunts a little at first but settleslout in about 10 to 15 minutes Hi side is 221# sub cooling on condenser is 5*f but it was evening and cooling down (84*f odt) but I expect that to drop a little as it gets warmer Super heat is at about 8-9*f

it might be a little short on charge but probably less than a half a pound
what I need to do is put a sight glass on it now

 

[hrdwrkingacguy]

Re: Hvac/r

Sight glasses are worthless...You seem to be a little overcharged actually...Possibly due to a little less airflow then you need or a dirty filter...To much refrigerant in the indoor unit and the outdoor unit is a little low, based on superheat and sub-cooling on a TXV...Is the bulb between 11 o'clock and 1 o'clock and strapped really tight and insulated??? If its an adjustable txv I would set it to 10 - 12 if the lineset isn't super long and see if the subcooling gets to like 8 or 9...running 5 degrees of subcooling you could lose your liquid seal in the liquid line...

It seems really close though and probably isn't worth any more trouble...