Looking for some tech advice with A/C compressor overloading

[SumGuy]

I'm hoping there's some HVAC guys here that can follow this.

I've got a Lenox condensing unit (LSA090C) that is rated for 7.5 tons and looks to have been installed 1998 - 2004. R22. 3-phase compressor.

Nameplate RLA (Run-load amps?) says 24.7. Not sure if that's all 3 phases added or not. My clamp on meter says each phase is drawing 20 - 25 amps.

Nameplate also says design pressure is 144 / 278 (psi, lo / hi).

I'm measuring about 75 psi on the suction side at the compressor. I haven't measured the high side, I probably don't have a gauge that can do it.

This unit has worked perfectly for the 2 decades that I've owned the premesis, has never had any service (except by me). I seem to have wired-out a high-side cut-off switch, could have been 10 years ago.

Two days ago, something happened. The compressor went into thermal overload. So I cut the power to it. After a few hours I powered it up again, it ran for maybe 15 minutes and cut out again. While it was running, the liquid line between the unit and building was warm, suction line was cold. Ambient temp probably 90. Exhaust air from unit was hot. There was some cooling inside the building, but air didn't seem to be as cold as I remember. Shut the unit down for the rest of the day. Early this morning, ambient was maybe 75, the unit ran for 30 minutes before again thermal overload, shut down.

So Like I said, I measured low-side pressure to be 75. It has a sight glass in the liquid line running beside the unit. Indicator color is green (no legend, I'm assuming green = no water). But I see a fast-moving stream. I guess these are commonly called bubbles? I'm not supposed to see this - right? I'm not supposed to see anything? This would ordinarily mean low charge? But can I have low charge and a correct low-side pressure? Would a low charge cause compressor overload?

Would adding more freon clear up the bubbles, and not raise the low side pressure, and solve the compressor overloading?

Or is the problem in the expansion valve? (it's thermal, with bulb). These are adjustable, is it worth going there?

 

[CDX825]

Low side pressure is in the ball park. The bubble in the sight glass and compressor over loading sounds to me like a head pressure issue. Dirty condenser coil or the condenser fan isn't moving enough air. Need to verify what the high side pressure is running.

 

[Nukeman7]

Low side pressure is in the ball park. The bubble in the sight glass and compressor over loading sounds to me like a head pressure issue. Dirty condenser coil or the condenser fan isn't moving enough air. Need to verify what the high side pressure is running.

^^^^This right here. You should clean the condenser coil fins if not done this season. Don't need anything fancy, just follow the video below.

 

[SumGuy]

Condenser coils are clean. The fan moves a lot of air.

The evap coils were a mess, on the inside, I did clean them today. Compressor still went into overload.

I understand that R22 high-side pressure has a wide range, not sure how useful that measurement would be. I know that when recharging my car A/C system from a can, that a low low-side pressure is 100% indicator of low freon, but when low side pressure is correct, and nothing else in the system has changed, it's got to be the TXV - no?

 

[SumGuy]

When the system pressure is measured when it hasn't been running for a while, presumably from either the low or high port (because they're going to be at the same pressure?) - does this pressure have a name? Like some sort of static charge pressure? Does it tell you anything?

I'm going to put the TXV bulb in hot water and see if that does anything.

If I remove the nut that's holding the spring, will the pin pop out on me? Will I lose any freon? Even if just for a second, and then I put the spring and nut back in, maybe if there's any junk in there - it will get cleared out?

 

[CDX825]

Standing pressure won't tell you much.

Don't pull the TXV apart unless you know what you are doing. Yes you will lose freon if you take it apart.

If the txv was stuck closed your low side pressure wouldn't be in range. Very possible you have a restriction before it such as a plugged filter drier.

Again if you could take a high side reading it would give more insight as to whats going on. Condensing temperature should be roughly 30 degrees over ambient temp with and R22 system.

Its also very possible the compressor is just on its way out and nothing else is wrong with the system.

 

[oil pan 4]

This is how I do it.
Assuming it's running like yours.
Always check the air filter. Look for primary and secondary air filters, about 96% of the time there's one, sometimes there's two singles working in parallel about 1% of the time there's a primary and secondary not located on top of each other.
Check the fan and air handler, for ice and heavy dust. Sometimes someone will run it without a filter then suddenly remember it doesn't have a filter when it stops working and put one in after everything is clogged up with dust. Obviously it still don't work.
If it's got low psi on the low side and the evap is iced and the fan or fins aren't too dirty it's probably got a low charge.
For the outside unit make sure the fan is blowing good and make sure the fins are straight, not covered with grass or packed with dirt. If you had a weak condenser fan or clogged fins your low side pressure would be high.

 

[JHZR2]

Standing pressure won't tell you much.

Don't pull the TXV apart unless you know what you are doing. Yes you will lose freon if you take it apart.

If the txv was stuck closed your low side pressure wouldn't be in range. Very possible you have a restriction before it such as a plugged filter drier.

Again if you could take a high side reading it would give more insight as to whats going on. Condensing temperature should be roughly 30 degrees over ambient temp with and R22 system.

Its also very possible the compressor is just on its way out and nothing else is wrong with the system.

Static pressure will simply tell you if you have liquid in the system, or if the unit is severely undercharged.

The tables for R22 vs ambient should be anywhere.

I can’t imagine trying to diagnose more than this and cursory low side number without a set of proper gauges.

OP should get some and report back all relevant numbers, ambient temp, static pressure after a long sit, high and low side operating at steady state, coil temperature, etc.

 

[SumGuy]

The condenser coils might have been dirty after all. I washed them down with a garden hose, with a fan spray nozzle. Funny thing - the few times I ran the unit after that, I really couldn't feel any heat coming off the condenser fan breeze.

Compressor amps were down a little. At 208/3-phase the rated load amps is 24.7 and I was seeing 20.

With the TXV bulb in cold water, the liquid line was warm, there was some ok cooling coming off the evap coils (the first 1/4 or 1/3 of it). Sight glass was still showing a stream, so a mix of air and liquid I guess. Really can't tell which direction its flowing. Compressor still went into overload after about 10 minutes. Have to wait an hour or two for it to reset.

With the bulb in hot water, the liquid line felt cold at the evap coil, maybe even also near the sight glass. The tiny distribution tubes (about a dozen of them) coming of the TXV were ice cold, too cold to touch for more than a few seconds, dripping with condensation. Evap coils still only partially cold. Sight glass still showing an air/liquid stream. I let it run for 5 minutes and then shut it down.

This model condensing unit has a reciprocating compressor, the model under this one has a scroll compressor. So I'm fairly confident I don't have a phase issue. This got me thinking if any power utility has ever changed the phases maybe during an outage / repair and not tell anyone. That would be - bad.

I'm having an HVAC guy come by tommorrow and do a diagnostic. I talked to him for about 20 minutes, told him what I knew about the system, he says with a low-side pressure of 70 psi he can't see how the system is low on R22. He also didn't think that seeing air/fluid in the sight glass was abnormal. I wonder about that - I thought the liquid line had to be totally liquid, especially at the TXV.

 

[facility1]

plugged or kinked cap tube?

 

[Fitter30]

Condenser coil is probably a split coil. To see if it is need to pull the top of the unit and it will two coils back to back. Opposite piping end the two coils will be held together by clips or screws or plastic wire ties. The inside coil will be dirty on the face of the coil The two coils will split about 80%. Piping end the coils will be 14" to 18" together when split. Wear gloves while splitting the coils fins can cut. Can rest the coils on a 1" board to wash underneath coils.

 

[SumGuy]

Ok, here's what happened.

I cleaned the condenser coils, and right away there was no heat blown out of the condenser by the fan. Put plastic bags coving all the coils, then there's heat again.

Had a tech guy come by, first visit he just connects his guages and reads some temps. Suction line and liquid line pressures are lower than they should be. I thought suction line pressure was ok (about 70 psi) but since cleaning the condenser it dropped to I think 50. Sight glass still shows a "visible" stream, so not a full liquid stream (which sort of looks like nothing is there).

The plan - obtain a new tank of R422b, remove any existing R22, fill the system with R422b, change a few schrader valves, and dump in a serving of "AC leak freeze pro" ready to use leak sealant.

This was done today. The installation guide for this unit says that with a 24 ft line set, the system should have 15 lbs R22. We pulled out 3.5 lbs (!). Didn't pull down to a vacuum, left it with some positive pressure and then dumped in 15 - 16 lbs R422b. Turned the system on - it ran and ran, compressor is not going into thermal overload. Yay! Sight glass showed a bit of a stream (so some bubbles) some times, other times no bubbles. Premesis temp and humidity came down quickly.

The remainder of the R422b was pumped into another can (because of ridiculous deposit on new can). I now have a can of about 10 lbs of R422b and 3 lbs of R22 that I can do with what I please. If my home A/C needs a top-up with some R22, I now have some. I'm told this stuff goes for $200 a pound (Can-Bux) on the grey market. The 25 lb can of R422b cost me $900 but I still have 40% of it left over. Paid the guy a few hundred cash, and everybody's happy.

 

[mk378]

The compressor is cooled by the cool gas returning from the evaporator, so with a very low charge it can overheat. This also happens in car systems.

The dirty condenser that you thought was clean was keeping the pressure up thus complicating the diagnosis.