Lennox 13HPX problems...

[cvairwerks]

We've got a Lennox 13HPX system that was installed about 10 years ago. It's been reasonably trouble free until last year. We started to get random low pressure lockouts on it. We had the coils cleaned, charge checked and it seemed to quit for a few months. Starting in March, it began again. Tech checked charge pressures, verified them by the in unit charts for the configuration we have. In April, after it happening several times of a weekend, we had the tech out again and everything was within book numbers. The only thing he noted was a tiny ticking in one bearing on the condenser fan. Not bad enough to change, but something to be planning for.

Fast forward to June and the unit is going into lower pressure cutoff numerous times a day, like as many as 8-10 times. AC company owner had told me how to reset things back in March and said that they were starting to get more and more calls for the same thing. He suggested that if it continued, that we would need to swap the control board. Got frustrated enough last week and ordered a new, upgraded board and swapped it out on Sunday. Unit worked flawlessly til last night, when it started to go back into low pressure cutoff again.

I know if we get a slight power spike or droop, it will send the unit into this mode. Any idea of any power conditioning I can install in the unit to maybe stop this? The wife and youngest son are tired of having to go cut off the breakers, wait for a couple of minutes then reset them so the unit will reset. This is getting to be a huge problem as summer heats up and I'm not where I can drop $20K to replace and upsize the system right now. Nor could I deal with having the hose torn up for a week to do all the work it would entail.

 

[American Locomotive]

The first thing you need to do is actually find out is if the pressures are genuinely dropping too low. If it's doing it 8-10x a day, a tech should be able to see it happen. If you don't want to pay a tech to babysit your unit, you can buy a service gauge yourself. They aren't too expensive.

 

[chinboys]

If past checks show the high and low side refrigerant pressures to be in specs, a control board being replaced and now, power sagging... Perhaps the low pressure sensor needs to be checked and replaced. Or jump it out.
But you need to monitor the pressures especially the low side or suction pressure. It is important to have adequate "cool" lower pressured refrigerant vapor to cool your compressor.
Sagging power isn't great either as it will strain the compressor to elevate the refrigerant'pressure before your expansion valve drops it.

 

[4x4Pete]

I am unfamiliar with that particular unit, but I have experienced failed tx valves that cause low pressure conditions. The drive pins that open the valve or the valve itself was sticking, so that the valve wouldn't modulate correctly. Superheat and subcooling fluctuations would tell the tech that this is happening, but it needs to watched long enough to diagnose. He can't be in a hurry.

 

[cvairwerks]

Last two times we put the gauges on, we monitored them for about an hour each time. Pressures were rock solid. Didn't have a failure then or the following several weeks.

The only thing that hasn't been visually checked or sniffed, is the line set from where it penetrates the outside wall to the a/c closet penetration. To get to it between those two locations would require significant destruction.

When we've had sagging power, it's almost always for under a couple of seconds and rarely drops below 210 VAC. Below that, and I've got a bunch of 120 VAC stuff that will reboot after a several seconds of low power.

May talk to the a/c guys next week and discuss simply shotgunning it and replace the high, low and tx valves to see if it cures things.

 

[fitter30]

Recording low pressure app alert. $75 with problems like your having could be a low pressure sensor going south and till it fails completely changing it may or may not fix the problem. Expansion valves don't normally fail like this. Bulb lose charge they fail closed. Biggest problem I've seen is a bulb not in correct place, loose on the pipe, not insulated or corrosion between bulb and pipe. This manual looks like it dates from 9/05. Page 7 & 8 low pressure control in this unit is a out of refrigerate control tripping at 25 lbs ( if that is true I'd bypass it for a day or two). High pressure is a true hp control.
www.amazon.com/Elitech-PGW-500-Wireless-Pressure-Waterproof/dp/B07514PS6Z/ref=asc_df_B07514PS6Z/?tag=hyprod-20&linkCode=df0&hvadid=693071814688&hvpos=&hvnetw=g&hvrand=13889306306162216578&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9023792&hvtargid=pla-763179794869&psc=1&mcid=02f817f819ac3577b2d1285fb204eebd&gad_source=1

https://www.google.com/url?q=https://www.hvacpartsshop.com/content/lennox-air-related-manuals/13Hpx%2520Series.pdf&sa=U&ved=2ahUKEwjTnu7GrK6HAxVRlIkEHZMfAn4QFnoECAUQAg&usg=AOvVaw03k6LKChB3uNgLqmW9os5D

 

[Jim greengo]

We've got a Lennox 13HPX system that was installed about 10 years ago. It's been reasonably trouble free until last year. We started to get random low pressure lockouts on it. We had the coils cleaned, charge checked and it seemed to quit for a few months. Starting in March, it began again. Tech checked charge pressures, verified them by the in unit charts for the configuration we have. In April, after it happening several times of a weekend, we had the tech out again and everything was within book numbers. The only thing he noted was a tiny ticking in one bearing on the condenser fan. Not bad enough to change, but something to be planning for.

Fast forward to June and the unit is going into lower pressure cutoff numerous times a day, like as many as 8-10 times. AC company owner had told me how to reset things back in March and said that they were starting to get more and more calls for the same thing. He suggested that if it continued, that we would need to swap the control board. Got frustrated enough last week and ordered a new, upgraded board and swapped it out on Sunday. Unit worked flawlessly til last night, when it started to go back into low pressure cutoff again.

I know if we get a slight power spike or droop, it will send the unit into this mode. Any idea of any power conditioning I can install in the unit to maybe stop this? The wife and youngest son are tired of having to go cut off the breakers, wait for a couple of minutes then reset them so the unit will reset. This is getting to be a huge problem as summer heats up and I'm not where I can drop $20K to replace and upsize the system right now. Nor could I deal with having the hose torn up for a week to do all the work it would entail.

Did they ever try replacing the pressure switch?

 

[bonneyman]

Did they ever try replacing the pressure switch?

Good point. Even if that's not the original problem a pressure switch has cycled on and off several dozen times it could start to get weak and trip at a different pressure than it's rating.
Same thing can happen with electrical switches, like circuit breakers.

 

[pcmeiners]

"When we've had sagging power, it's almost always for under a couple of seconds and rarely drops below 210 VAC."

Assuming this during the day, most power anomalies are in the wee hours of the mourning. Aside from making sure the switch is pressure OK, what is your unit drawing in amps, how far from the main box it, what is wire size.
If the a fore mentioned are in spec, and the utility company is at fault, contact them. 210 vac is more than a sag... it is denial of service.
Try getting the utility to remedy the problem, if they do not respond, call and write your state utility commission.

 

[brewchief]

210 volts won't present an issue to the condenser, it will be more of a problem on the low voltage control side.
Every Lennox condenser I've seen in recent years has a voltage tolerance from 200 to 253 IIRC. They do this so it can be used in buildings with 3 phase that supply 208v.

The indoor fan doesn't stop running shortly before it drops out on low pressure by chance does it?

 

[bonneyman]

Some years ago now locally we had power "sagging" issues, especially on the outer edges of the city. During the summer those folks living on the outskirts of the city on the east and northeast side had more issues with brownouts and power outtages. It got to be if folks in those areas called me noon to mid afternoon with no A/C I'd recommend they turn their stats off, just sit tight till sundown and try their units again. Rarely can I recall those customers calling the next day saying they were still out. Once the demand dropped and the power company fixed the grid issues power came back up and stuff worked fine.

 

[American Locomotive]

210V is way out of tolerance - that's a nearly 17% drop. That could definitely cause issues if the Lennox controls are running off a 24v transformer. You might need a logging multimeter and have it monitor voltage, and see if voltage sags correspond with the errors the unit is generating.

 

[fitter30]

210V is way out of tolerance - that's a nearly 17% drop. That could definitely cause issues if the Lennox controls are running off a 24v transformer. You might need a logging multimeter and have it monitor voltage, and see if voltage sags correspond with the errors the unit is generating.

Post 6 for manual
Unit rated not at 240vac but 230 - 208 vac. Page 1 model number
Page 4. Under control box 24vac comes from indoor unit. Don't know how many units I've worked on and the 240 vac transformer tap was never changed to 208 vac on older equipment. Would be a good idea to check the trans to see what primary voltage is and see if there's a tap. If the voltage is 240 vac like to know what the secondary volts are?
Look at third paragraph down from top 20.4 vac

https://www.google.com/url?q=https://www.nhp.com.au/-/media/Project/NHP/Sites/Shared/White-Papers/Files/NHPTNL54.pdf&sa=U&ved=2ahUKEwjT6qTUoLGHAxWWlYkEHY1ZBDoQFnoECAUQBg&usg=AOvVaw2rlo84yh0_W1iT6DAEljVE

 

[American Locomotive]

Keep in mind that "208-240v" doesn't necessarilly mean 208-240v while in operation. Voltage and sensor references are often established on initial power up for example.