Air conditioner question

Steve@Advance

Well-known Member
Looked at a coworker's home AC unit this evening. It's a 3 ton, R22, older system with orifice tubes, the condenser unit has been replaced with a newer scroll compressor.

This system has a history of a slow leak. In the past it has worked well when fully charged. I had the evaporator out 2 years ago repairing a condensate leak, and the coils were cleaned then.

Yesterday he asked if I could add some refrigerant, it wasn't cooling properly.

Went by this evening and it was about 80 in the house, blowing cool but not cold air. The return line was sweaty cold back to the compressor. Put the gauges on, 90PSI on the low, 300 high. It was about 97* outside. I told him it didn't need refrigerant, he wanted me to put some in anyway, so I did just to see, but it did nothing but raise the high to 320PSI.

The air coming off the condenser coil is barely warm and the compressor is very quiet, like it's not working quite as hard as it should. I turned the unit off for a few minutes, let it unload pressure, and when I turned it back on the compressor sounded like it was pumping as it should (already had the gauges off), then in about 3 seconds something sounded like a pressure relief valve popped off, making a hissing sound that somewhat diminished but continued to hiss. Whatever it is is internal, nothing was escaping. BTW, this is a straight AC, no heat pump.

Any ideas what is going on?
 
With a condensing temp of 97º the high side pressure should be under 200 PSI.

The condenser is dirty, or the fan isn"t working properly, or the system is overcharged or there"s air in the system.

It would be interesting to zap the condenser with an infrared thermometer.
 
The history with leaks sends up a warning of possibility for air & moisture from guages and hose being put in during some of the recharges and/or at time coil was removed.
There might be an ice blockage at one or more metering tubes. A good deep 10+ hour vacum and new drier might help it. I assume you looked for dirty condenser coils. Always look for split coils as in two seperate layers of coil and fin. Those things can look clean on both sides but when pulled apart be totaly clogged in between. It would have been good to had an amp meter on compressor during your observation to see if amps changed along side sound.
 
This System is seriously overcharged. Refrigerant nweeds to be recovered. system evacuated and recharged to correct levels
 
I'm with Chuckles. The pressures seems high for low side as well. Did you have a tempreture probe on low line to compare the line temp with the gauge temp? I bet at 90 psi on the low side, superheat is nonexistant.
 
The scroll compressor has an internal bypass that is activating due to excessive pressure. The smoking gun is your statement that within a few minutes you hear a pop and continual hissing sound...

Go with the above listed suggestions as far as recovering and recharging the refrigerant. Air (non-condensible) in the system will show a swinging head pressure...it will not stabilize. Along with the swing in head, the suction will also swing. Once the internal bypass releases, the compressor does little if any appreciable cooling.

Possibly consider finding out the subcooling requirement and charge to that temperature on the liquid line. That will ensure the proper refrigerant level in the system as accurately as utilizing the superheat method but its not quite as difficult to get dead on.

Somewhere inside the electrical panel there should be a charging chart that directs you to superheat, subcooling or at least the factory charge which should be able to accomodate the evaporator plus 15' of line set. Of course, the chart will probably be damaged or totally missing.
 
Do the inside coils have an txv(expansion valve)? Had to replace mine on both units(up and down stairs). High head pressure and low suction.
 
My first guess is with 90 psi on the suction side and condensate on return line back to comperssor is unit is over charged, especially with 300 psi head pressure.

I would have to look at guage to give you the exact suction pressure. I would expect perhaps 70-75 psi on a hot day.

Reclaim some of the freon slowly. You still want some condensate on suction line, especially on a hot humid day.

Check to see if the condensor is clean. That could up the head pressure, boost the suction and lose cooling in a very hot day.

My 14 year old rudd, r22, has an expansion valve and pressure switches. So far no leaks. Had to clean condensor once.

I read the new 410a systems won't hold up if they have a slow leak, suck in a little moisture.

The older r22 systems are more forgiving. IMHO, it a fact of life that sooner or later all refrig, dehumidifiers, ac and HP will leak and some leaks are impossible to find.

I was determined to find the leak in some small unit. Removed all electrical and put it under water. The last dehumidifier had over 30 pin hole leaks in the evaporator. I scrapped it out.

Let us know what you find.
 
Massey Man, the internal pressure relief, that makes sense, that's exactly what it sounds like is happening.

Whatever has happened did it on it's own. The system worked all summer. Last time anything was done was last fall, I added some refrigerant. The gauges are stable, so I don't think there is air in the system.

If the orfice tubes are iced or clogged, wouldn't that be the same as a stuck shut TXV? That should show low low side pressure, but my low side is high. Always has been high, even when it was working. Last fall when I charged it I just charged until the low line flashed cold. Since the condenser unit and the evaporator are not matched, would the superheat/ subcooling method still be applicable?

I need to get back over there and do some more troubleshooting, check some temps, look things over closer.

Thanks for the help!
 
Simple to figger......... Ambient temperature at condenser plus 40 should equal the discharge pressure at condensing unit. Ex. 90 Deg outside temperature + 40 equals 130 deg. Using a pressure chart for R-22 the discharge pressure should be approx. 297 pounds, gauge. for 130 deg. The suction pipe should be cool and sweaty at the condensing unit with indoor fan turning and thermostat calling for cooling.

The evaporator (inside coil) pressure should be at approximately 40 to 45 deg. The suction pressure at the compressor should be approximately 69 pounds, gauge.

This is a general procedure for all R-22 systems, regardless of make.

I would assume the condenser fan is turning ok. also, the condenser is clean of dirt.

Sometimes the compressor bypass (over pressure valve, internal) will "pop-off" if there is a restriction somewhere in the system that makes the compressor pressure too high.

Moral to the story....go with the temperatures and pressures, first. An overcharge will make the head pressure too high, while the evaporator pressure will be too high, also.

HTH John,PA
 
Make sure the system was re-filled with R-22 or equivelent after the compressor change out.

These days, there are a lotta of refrigerants out there and sometimes they are used to replace the R-22. Are you sure they didn't use R-410a in the system. Otherwise the pressures will be all outta wack.

John,PA
 
(quoted from post at 12:46:26 08/28/14) Massey Man, the internal pressure relief, that makes sense, that's exactly what it sounds like is happening.
The gauges are stable, so I don't think there is air in the system.

If the orfice tubes are iced or clogged, wouldn't that be the same as a stuck shut TXV? That should show low low side pressure, but my low side is high. Always has been high, even when it was working. Last fall when I charged it I just charged until the low line flashed cold. Since the condenser unit and the evaporator are not matched, would the superheat/ subcooling method still be applicable?

Thanks for the help!

What you may have, with the inclusion of the statement that its always ran a bit high on the suction side is the possibility of an improperly sized fixed orifice.....IF in fact it has the fixed orifice metering device and not just capillary tubes from years ago.

Is there a brass bodied "socket" that requires two wrenches to crack open?? If so, inside that socket is a "fixed restrictor" that may be the culprit causing the continual high suction under NORMAL conditions.

Its high now because of the bypass condition though. I'd clean the condensor thoroughly first then proceed with gages on and monitoring while the water evaporates off of the condensor surface. Have an amprobe on the compressor common leg and look for full load amps (or close to it) just prior to internal relief. If there are no non-condensibles in the system, the head will remain steady without fluctuation and slowly rise to the point of bypass if overcharged.

However, in the bypass condition, the head pressure may NOT fluctuate because it is bypassing. You will be able to determine the evidence of or lack of non-condensibles while monitoring the pressures as the condensor dries out just prior to entering bypass.

As far as superheat and subcooling, the answer is yes, it is still applicable but you'll have to "interpolate" to get it dialed in as it is NOT a matched set. That'll be the "seat of the pants" method.

If the condensor is a standard 9.0 or 10.0 SEER with a mixmatched coil the 35 degree over ambient method should get you in the ballpark...but monitor subcooling during the adjustment as if it is waaaaayyy too high or waaaaayyyy too low it should be fairly obvious. 3 or 4 degrees sub cooling is on the low side and 25 or 30 degrees subcooling is on the high side. If it were me I'd shoot for 12 to 16 degrees sub cooling to start. The TD across the evaporator should be near to 20 degrees as possible when your are done.

If some of the capillaries are restricted or partially so, the resultant suction pressure will be low as you suggested above.

Apologizing for the lengthy response.....Good Luck sir and let us know.
 
John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
 
(quoted from post at 17:26:23 08/28/14) John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
don't suppose this unit is old enough that it has valves that allow you to shut off feed to evap so as to allow you to judge whether the compressor is capable of pulling a vacuum? A poor compressor can't generate much differential.
 
(quoted from post at 15:10:27 08/28/14)
(quoted from post at 17:26:23 08/28/14) John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
don't suppose this unit is old enough that it has valves that allow you to shut off feed to evap so as to allow you to judge whether the compressor is capable of pulling a vacuum? A poor compressor can't generate much differential.

Unless something has changed with the newest generation Scroll compressors, it is generally NOT recommended to pump them down like an old reciprocating compressor. The manufacturers typically warn that damage to the scroll internals would/could be the result.

Thats the first thing we'd do with a semi-hermetic compressor or an old recip to ensure it had the capacity to pump though, if the valves were suspected bad.
 
If you are areading 90 # pressure on the low (suction) side, the evaporature is approx. 55 deg. According to the R-22 scale.

I assume this is a capillary fed evaporator.
I would tend to believe that the system is still overcharged to put that pressure on the evaporator. To bring the temp down, I would probably remove some R-22 to make the evaporator pressure in line with a 40 deg. pressure.

Sometimes the condenser will hold more refrigerant without being "overcharged".

So, keep removing a few pounds of R-22 from the system and see how the head pressure holds up to the ambient temp without being too low.

You stated that the condenser did NOT match the evaporator. Sometimes it can get tricky to try to put a replacement condenser to some systems. Some of the newer equipment will be capable of putting off more BTU's than the evaporator can stand without matching up the expansion devise. Sometimes the device is simply an orfice (piston) that was sized to the original manufacturer's spec's.

For instance, changing a 3 ton condenser (EER of 10 or higher) to an older evaporator can cause too much cooling for the evaporator, so, lots of times we go by the pressure charts rather than the orig. factory charging scale for the orig. equipment.

So, I would go by the evaporator temp (40 deg) and do not worry that the condenser is reading a lower head pressure than normal. Probably you will still have a sweaty suction pipe at the compressor.

Hope you get her running.
 
(quoted from post at 19:49:36 08/28/14)
(quoted from post at 15:10:27 08/28/14)
(quoted from post at 17:26:23 08/28/14) John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
don't suppose this unit is old enough that it has valves that allow you to shut off feed to evap so as to allow you to judge whether the compressor is capable of pulling a vacuum? A poor compressor can't generate much differential.

Unless something has changed with the newest generation Scroll compressors, it is generally NOT recommended to pump them down like an old reciprocating compressor. The manufacturers typically warn that damage to the scroll internals would/could be the result.

Thats the first thing we'd do with a semi-hermetic compressor or an old recip to ensure it had the capacity to pump though, if the valves were suspected bad.
K, ......so how do they propose that one determine the condition of the compressor?
 
Thanks Massey Man, that gives me several things to
check. I'll get back over there this weekend and
see what I find.

Thanks again!
 
(quoted from post at 20:18:47 08/28/14)
(quoted from post at 19:49:36 08/28/14)
(quoted from post at 15:10:27 08/28/14)
(quoted from post at 17:26:23 08/28/14) John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
don't suppose this unit is old enough that it has valves that allow you to shut off feed to evap so as to allow you to judge whether the compressor is capable of pulling a vacuum? A poor compressor can't generate much differential.

Unless something has changed with the newest generation Scroll compressors, it is generally NOT recommended to pump them down like an old reciprocating compressor. The manufacturers typically warn that damage to the scroll internals would/could be the result.

Thats the first thing we'd do with a semi-hermetic compressor or an old recip to ensure it had the capacity to pump though, if the valves were suspected bad.
K, ......so how do they propose that one determine the condition of the compressor?

At the seminars I attended the manufacturers recommend a pump down to not less than 20 psi on the suction side to determine its ability to "pump" adequately. In the old days, a recip could be pumped well into a vacuum... The compressor could be used to "pump itself over" so work could be done on the low side of the circuit...repair/replace evaporator, change LL solonoid, replace TXV etc. But not anymore with the scrolls.

So I guess in short, a pump down could be used to determine the compressors viability if you strictly adhered to the 20 psi limit. So in that essence I stand corrected.

In this case where we mostly agree there is an excess refrigerant charge, it wouldn't be recommended until a percentage of r-22 is removed I'd think. There's limitations to what the condensor can contain and limitations to what the scroll can pump into it without entering bypass during the process.
 
(quoted from post at 08:26:34 08/29/14)
(quoted from post at 20:18:47 08/28/14)
(quoted from post at 19:49:36 08/28/14)
(quoted from post at 15:10:27 08/28/14)
(quoted from post at 17:26:23 08/28/14) John, our calculations agree. The 300 PSI on a 97* day is ok. The 90 PSI on the low side is not normal.

The evap coils are clean, good air flow. The condenser coils look good, air is flowing but it's picking up very little heat.

Something must be restricted for the low side to be that high and the compressor bypassing, but what? If it were clogged/frozen metering orifices wouldn't the low pressure be too low?

Whatever it is happened on it's own. It worked all summer no complaints. He says no one has worked on it since last fall when I added some refrigerant.

Thanks!
don't suppose this unit is old enough that it has valves that allow you to shut off feed to evap so as to allow you to judge whether the compressor is capable of pulling a vacuum? A poor compressor can't generate much differential.

Unless something has changed with the newest generation Scroll compressors, it is generally NOT recommended to pump them down like an old reciprocating compressor. The manufacturers typically warn that damage to the scroll internals would/could be the result.

Thats the first thing we'd do with a semi-hermetic compressor or an old recip to ensure it had the capacity to pump though, if the valves were suspected bad.
K, ......so how do they propose that one determine the condition of the compressor?

At the seminars I attended the manufacturers recommend a pump down to not less than 20 psi on the suction side to determine its ability to "pump" adequately. In the old days, a recip could be pumped well into a vacuum... The compressor could be used to "pump itself over" so work could be done on the low side of the circuit...repair/replace evaporator, change LL solonoid, replace TXV etc. But not anymore with the scrolls.

So I guess in short, a pump down could be used to determine the compressors viability if you strictly adhered to the 20 psi limit. So in that essence I stand corrected.

In this case where we mostly agree there is an excess refrigerant charge, it wouldn't be recommended until a percentage of r-22 is removed I'd think. There's limitations to what the condensor can contain and limitations to what the scroll can pump into it without entering bypass during the process.
hank you.
 

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