A/C not putting out enough cooling, gauges not happy

[Larry2]

Well, the old hands around here will recall quite a while back, I was working on my Lennox heat pump/ Air con unit which was producing inadequate cooling while the gauge pressures didn't seem quite right. That system also had endured repeated shutdown on compressor temp due to the condensor fan motor shutting down. That issue was solved, but who knows what damage occured to the compressor?

Today temperatures were cool enough to risk a tinker on my unit and I finally assembled the recycling gear, vac pump, parts and whatnot to proceed. The issue before was inadequate cooling with low high side pressure and high low side gauge readings. Folks will recall back then I throttled back the blower, adjusted charge and measured system performance numerous time, all to no avail.

I obtained a factory 4 ton R22 expansion valve for this system. So this morning, I vacuumed out a new recovery tank, set up my Promax Minimax and recovered the system charge. I'm a newbie at this recovery biz, we used to open the manifold and walk away 30 years ago. So I don't know why I was surprised, but through the process, I had to stop, put cooling fans across the recovery tank and let pressures and temperatures of the tank drop. Finally, with the charge pumped out, I installed a factory fresh 4 ton expansion valve in place of the 3 ton valve that was configured before in this 3.5 ton system. Next I vacuumed the system for two or three hours, closed the valves, watched gauges and vacuumed some more. When I was happy the vacuum was solid, I recharged the system using as much of the old charge as would return from my recovery tank and then added additional charge from my service tank. This left me with 80 PSIG in my recovery tank. I would like to know how much R22 in pounds remained in this tank which seems to be 1400 cubic inches. How would I calculate this?

Anyway, I continued charging, checking amperage draw, subcooling and whatnot. The low side gauge is too high at 80 PSIG +/- which is worse than before. The high side gauge is only 140 PSIG with outdoor temps today of 85 degrees F. I'm getting around 12 degrees drop across the evaporator which is similar to before. The suction line was around 62F with a suction line pressure between 78 and 82 PSIG. Superheat is still too much.

I attempted charging to subcooling specs for the condensor and as I add more charge, the high side creeps up but the low side stays mostly unchanged. I get a subcooling of 7 degrees while the spec is 12 +/-2. As I add more charge, mostly the low side gauge creeps higher and the high side gauge stays unchanged. I could add more until subcooling is right, but past experience with this unit is it won't make significant difference. It was a few pound charge between bubbles vanishing and finally stopping work tonight with 7 degrees subcooling. I'm having an intermittent lead in my thermometer, so I don't have a full set of system temperature readings tonight.

Am I looking at excessive internal pump leakage in a worn out scroll compressor or should I direct my attention elsewhere?

[Brian_UK]

Larry, you can't calculate the amount left in your recovery tank by checking the gas pressure.

You should have weighed the amount that you took out and weighed back in the same, or correct amount.

[Larry2]

Thanks Brian. I guess that's why I didn't find any info in the texts other then weighing the cylinder. I thought if there was only gas, it could be calculated. This cylinder's a bit stout and my digital scale doesn't go that high.

I found some fog in the cabin too. The high side gauge wasn't reading correctly because of a problem in the shrader valve for a high side safetly switch I was adding. That safetey switch piece is a kit with a copper loop Tee between the service valve the switch and creates a new service valve connection. It's a Trane piece I thought I would add for high pressure compressor protection. Anyway, I now have subcooling on the money with a high side gauge of 173 and low side gauge of 73. I think the readings are still wrong for the temps tonight. I'll buy a new digital thermometer tomorrow and get some system performance calculations done.

[Andy]

Well, the old hands around here will recall quite a while back, I was working on my Lennox heat pump/ Air con unit which was producing inadequate cooling while the gauge pressures didn't seem quite right. That system also had endured repeated shutdown on compressor temp due to the condensor fan motor shutting down. That issue was solved, but who knows what damage occured to the compressor?

Today temperatures were cool enough to risk a tinker on my unit and I finally assembled the recycling gear, vac pump, parts and whatnot to proceed. The issue before was inadequate cooling with low high side pressure and high low side gauge readings. Folks will recall back then I throttled back the blower, adjusted charge and measured system performance numerous time, all to no avail.

I obtained a factory 4 ton R22 expansion valve for this system. So this morning, I vacuumed out a new recovery tank, set up my Promax Minimax and recovered the system charge. I'm a newbie at this recovery biz, we used to open the manifold and walk away 30 years ago. So I don't know why I was surprised, but through the process, I had to stop, put cooling fans across the recovery tank and let pressures and temperatures of the tank drop. Finally, with the charge pumped out, I installed a factory fresh 4 ton expansion valve in place of the 3 ton valve that was configured before in this 3.5 ton system. Next I vacuumed the system for two or three hours, closed the valves, watched gauges and vacuumed some more. When I was happy the vacuum was solid, I recharged the system using as much of the old charge as would return from my recovery tank and then added additional charge from my service tank. This left me with 80 PSIG in my recovery tank. I would like to know how much R22 in pounds remained in this tank which seems to be 1400 cubic inches. How would I calculate this?

Anyway, I continued charging, checking amperage draw, subcooling and whatnot. The low side gauge is too high at 80 PSIG +/- which is worse than before. The high side gauge is only 140 PSIG with outdoor temps today of 85 degrees F. I'm getting around 12 degrees drop across the evaporator which is similar to before. The suction line was around 62F with a suction line pressure between 78 and 82 PSIG. Superheat is still too much.

I attempted charging to subcooling specs for the condensor and as I add more charge, the high side creeps up but the low side stays mostly unchanged. I get a subcooling of 7 degrees while the spec is 12 +/-2. As I add more charge, mostly the low side gauge creeps higher and the high side gauge stays unchanged. I could add more until subcooling is right, but past experience with this unit is it won't make significant difference. It was a few pound charge between bubbles vanishing and finally stopping work tonight with 7 degrees subcooling. I'm having an intermittent lead in my thermometer, so I don't have a full set of system temperature readings tonight.

Am I looking at excessive internal pump leakage in a worn out scroll compressor or should I direct my attention elsewhere?

Hi Larry

What about using you recovery unit to pump the gas out of the bottle into the condensing unit

Sound like with low head and high back pressure that the expansion valve is wide open, whats your superheat like?

You probably have to remove some charge



Kind Regards Andy

[Larry2]

Part way through tinkering on the system, the remote thermistor on my thermometer became intermittent. So I never got a chance to measure superheat. I was planning to return here with some readings once I bought a new thermometer but meanwhile the temperatures have turned cool. I get another shot at this next week and then I think we are done for the cooling season.

I did decant gas off to the cylinder once I discovered the problem getting the high side gauge to read correctly. I adjusted the charge for 12 degrees subcooling which is the procedure outlined on the unit door. This seems pretty particular about charge with subcooling value changing fairly quickly with charge. Subcooling changes quite more rapidly than suction side temperatures or pressures.

When I worked on this earlier in the season, the superheat was excessive. I have a hunch that with the 4 ton txv replacing the 3 ton that situation is even worse now.

Last time, with the 3 ton txv installed, decanting charge out of the system didn't improve performance and really only caused minor changes to the suction side pressure and temperatures. The subcooling changed quickly with charge amount but superheat didn't change much.

Both indoor and outdoor coils are clean and air flow appears to be adequate. A problem with air flow would cause low suction and problem with this system. I've juggled fan speed lower with no improvement.

What else could be causing loss of performance? Thanks!

[dirtyboy103us]

ok how about some more reading's like indoor wet bulb, dry bulb, amps on heater if any, amps on compressor you know the basic's
model # on units

80 psi on suction does not sound high on start up
but 140 sounds low, what's the compressor rated for
in amp draw and what's it pulling, type of compressor recip or scroll

going from a three ton valve to a four ton would only increase your suction

these are just guesses here with out the needed info

[Larry2]

We have some warm weather coming up. I'll come back with a full set of carefully done measurements.

I caused some confusion with my original post. The shrader valve wasn't opening properly for my high side gauge so the reading of 140 was incorrect. With that fixed, I was running around 185-190 PSIG high and 80 PSIG low. Subcooling was 12 after adjusting charge. Then my thermistor probe took a dump and progress stopped.

[dirtyboy103us]

With those pressures it does not sound to bad
still need others though to get it going, how's your light
bill, is it a little high, could you have a broken heat strip
or bad sequencer pulling a few amps and sending a little heat into the house with the cooling giving you a small t/d seen this many times. Just a few directions to go in to start with.....

[Larry2]

Well, I never got around to further tinkering. Last night it was around freezing outside and in heat pump mode, the system put out amost no warmth.

I'm thinking the compressor is at fault. The system worked quite a bit better before the repeated shut-downs of the condensor fan motor.

Getting cold now and resistance heat is costly. I guess it's time to get serious about solving problems.

[Jase]

larry,
I assume that the tev fitted is of external equalised type?
Is the phiall strapped onto the pipe sufficiently and is it a fixed orifice?

regards
Jase

[Larry2]

There is a txv in the condensor unit for the heat pump cycle and a txv in the evaporator for the A/C cycle. Both have external equalizer tubes. The evaporator txv includes a check valve for refrigerant path during heating cycle. The condensor contains a check valve in a filter/drier next to that txv.

I replaced the txv in the evap from a 3 ton to a 4 ton type, both VGA for R22. The larger rating valve made things worse. The system is 3-1/2 tons rating with a scroll compressor. It's not working well on heat or cooling.

[Jase]

Larry,
can you perform an efficiency test on the compressor?
Check and see if it holds a vac. Other than that you should maybe revert back to original design capacity of unit and alter gas charge.

regards
Jase

[Larry2]

How do you test a scroll compressor efficiancy?

The problems with poor efficiancy have plagued this system since installation but not as bad as now. It's possible the installer didn't do a proper evacuation. If there were non-condensibles in the system from the original installation, they are still there because I recycled the original charge rather than charging virgin R22 when replacing the txv. How would non-condensibles effect performance?

The performance problems were much worse following the repeated episodes of the condensor fan motor shutdown. This is the first time for using heat cycle since correcting the condensor fan shut-down problem and heat is not working well at all.

I have measured temperatures at the reversing valve. I don't see changes that indicate leakage in either heat or cooling configuration. I think this valve is okay.

Heat cycle passes through the bypass valve of the indoor txv bypass, so the system is configured exactly as original when switched to heat cycle. I checked subcooling again yesterday during cool weather and again get 12*. With cool weather, suction temperature and pressure were normal. They are both to high when the system can't keep up during summer. Yesterday, the evaporator was lightly loaded because the upper floor was not overly warm.

Is the scroll compressor design durable against high head pressure and overheating caused by condensor fan failure or does the scroll assembly loose it's precision and therefor develop higher internal leakage?

[taz24]

The two points you mention are.

1. Testing for air. Air in the system can be checked by shuting the system down and allowing the gas pressure's and temps to equalise. Do a pressure test on the discharge and measure the temp of the discharge line. Compare the standing pressure to the actual temp on a comparater or chart. Compare the difference. If the actual gauge-temp reading is higher than the ambient temp then it has a non condensable in it.

2. in cool weather the cond is more efiecent due to the greater temp diff over the cond. In the summer the ambient temp is higher and therfore the diff over the cond is lower causeing the system to stuggle if air is inside.

Cheers taz.