[NA] Broken AC Question

[Ted]

Since this is my go-to place for household items...

The compressor on our AC is broken (2008, Lennox 4-ton). The AC tech said that there was a weird compressor design they made about that time period that was a complete POS and if it overheated would trip an internal breaker that would basically run the freon around in a circle (instead of having a high side and a low side), but wouldn't actually shut off the compressor or condenser fan. IOW, all of the energy consumption, no indication other than your vents stop blowing out cold air. Will keep on running until you shut it off. If it cools down enough, it works again, but that seems to take around 12 hours. It picked a great time to quit on us. It was in the 90s over the weekend, in the 90s today, high of 99 tomorrow. I drove to work because it was too hot to ride the motorcycle... at 7:30 AM (ok it would've been fine riding in, but this afternoon would've roasted me).

Adding to that, our system is R-22, which apparently they don't make anymore (thank you, EPA) and the conversion ends up requiring a whole new unit (inside and outside). There is a possibility that the guy I just called can get an R-22 compressor/condenser/outdoor unit and just replace that. Our system is a 4-ton that has three zones - two downstairs (probably could get away with just one) and one upstairs. It is a combination AC/heat pump.

If it turns out we have to buy a whole new unit (hoping not, but we'll see) I'm wondering if it makes sense to get rid of the zoning and split the house up into two smaller units. Looking at the setup, I think it wouldn't be too difficult to do. The zoning ducts are all in the basement, so I think you could probably just remove the zone flappers and then disconnect the duct going upstairs, then connect it to a second unit.

The guy who came to diagnose the issue said that he sees this a lot with zoned units. Basically you have the same refrigeration capacity, but the zoning doesn't provide enough airflow to dissipate the cold from the cold side, and eventually you can get liquid refrigerant getting back to the compressor, which can cause the issues we had. I have no idea if this is true or not - I've never run into that in automotive AC, but I don't know any of the nuances of home AC. He mentioned one other option that he'd expect to be more reliable (and more efficient, something like 20 SEER vs 14-16) is a unit that will scale up and down depending on how many zones are open.

One other issue (which may just be perception) is that it feels like the upstairs vents aren't getting much airflow.

Interested in opinions on what makes sense to do. I'd rather just get this fixed less expensively vs putting in a whole new unit. Since the rest of the unit is only around 8-10 years old (house built in 2005, the setup was upgraded and zoning added in 2008 because they undersized it initially) I would rather not replace everything.

 

[Clark1961]

You are a twin guy, get 2 smaller units...

Mostly joking but a higher efficiency unit will drop the utility bill significantly. Just have to look at the $$ and make the call.

 

[Ted]

You are a twin guy, get 2 smaller units...

I tend to like that setup for multiple reasons, mostly that I think it ends up working better. Just like with airplanes, I don't mind if the utility bills are higher for a better solution.

Mostly joking but a higher efficiency unit will drop the utility bill significantly. Just have to look at the $$ and make the call.

So you're suggesting a single, higher efficiency unit over the two smaller units?

 

[rpadula]

Ted,

I'd suggest the hvac-talk website (http://hvac-talk.com/vbb/forumdisplay.php?1-AOP-Residential-HVAC). Got some good feedback and found a great installer on there when mine conked out last year. The equipment is not necessarily the deciding factor; you need someone who knows what they are doing.

There's probably no good reason to switch to two smaller units. That would be more expensive. You'd have to run a complete set of everything (wiring, pipes, circuit breakers, etc) for the second unit. If you haven't been having comfort problems, just fixing or replacing with new would be your best bet. 10 years is kinda at the edge of the fix/replace decision.

I looked at the advanced variable units that could hit 20+ SEER. Decided against it. They're DC drive motors with a bunch of electronics in the outside unit. Really skeptical of the longevity of those control circuits. That's a tough environment for electronics to operate. I wouldn't get twirled up about the extra efficiency.

P.S. What model #'s do you have on the indoor and outdoor units?

 

[Ted]

Thanks, Rich.

I wasn't having comfort problems with the current setup. It seemed to do the job just fine and we got the temperatures we wanted (until it broke). The comment the tech who came out said is that having a zoned system without a variable speed motor will shorten the life of the compressor. So that pointed towards one of the more efficient units. I, too, wonder about the longevity of the more complex items vs. just your standard "run it" setup.

I've never priced doing a total new unit or upgrading. In 10 years of home ownership (in 3 homes), this is the first time we've had an issue of this sort. The house in Ohio needed a new blower motor for the HVAC, but that was all. Obviously the two units would be more involved, and probably make more sense if we were building/installing new vs. repairing.

Laurie also reminded me that we have a home warranty still (bought the house 10 months ago), so we're going to call them to see if this is covered. They would obviously do the cheapest fix, but even if that gets us a few more years before needing to do a more significant repair, that'd be worthwhile since it's effectively free.

 

[bikert]

Another vote for going for higher efficiency units. I replaced my old 11 Seer units with 21 Seer variable speed units a couple of years ago and have been staggered at how much my electricity bill went down... I also installed Nest controllers at the same time. My summer electricity bill dropped to 1/3 of where it was. The whole process of installing the new units (inside and outside) may have introduced other benefits like fixing any ducting issues, insulation, etc.

 

[Ted]

Another vote for going for higher efficiency units. I replaced my old 11 Seer units with 21 Seer variable speed units a couple of years ago and have been staggered at how much my electricity bill went down... I also installed Nest controllers at the same time. My summer electricity bill dropped to 1/3 of where it was. The whole process of installing the new units (inside and outside) may have introduced other benefits like fixing any ducting issues, insulation, etc.

I'm fairly certain I have some ducting issues currently. I'm not sure what the current Seer rating is on this unit, but it does seem to me like it's on the lower end of the efficiency side. The bills so far this year have surprised me as I feel like they should be lower compared to the previous two homes and current cost of electricity still being fairly low.

 

[SCCutler]

2008 Ain't that old.

But the stuff Mr. AC Guy is telling you is riddled with bogosity. R22 is readily available, and I have never heard of a compressor that fails to a recirc mode like that.

Call the home warranty folks, report back.

 

[Clark1961]

I tend to like that setup for multiple reasons, mostly that I think it ends up working better. Just like with airplanes, I don't mind if the utility bills are higher for a better solution.



So you're suggesting a single, higher efficiency unit over the two smaller units?

Yes. A system with fully variable speed blower would probably deal with the zoning concerns assuming the ducting is set up correctly for balanced flow.

Unlike the poster who was concerned with motor controls I have no worries. The electrical side is pretty bullet proof short of a lightning strike. Variable speed drive technology is mature, just make sure it is fed the correct voltage. You shouldn't have to worry about voltage from your utility company just mentioning it because I've seen 1 situation where the drive failed and it happened to have slightly below spec voltage. That was 1 drive out of a hundred we were using.

I have whole house surge protection and assume you do too. If you don't have it, get it.

 

[Ted]

2008 Ain't that old.

But the stuff Mr. AC Guy is telling you is riddled with bogosity. R22 is readily available, and I have never heard of a compressor that fails to a recirc mode like that.

Call the home warranty folks, report back.

R22 is available, he said that the parts for R22 systems aren't anymore unless you can find New Old Stock. No idea if that's true.

Home warranty company has been called. They're coming out on Wednesday. Of course, that only covers up to $2k, so they'd likely end up saying they want to put in a whole system, but it'd at least be $2k cheaper than the base quote. I'll have several quotes by Wednesday and then we can make a decision.

In the mean time, I think I'll shop for a boat that has air conditioning. That seems like a good plan.

 

[SCCutler]

Again, my BS-O-Meter is pegging. When you get yourself home, send me a picture of the dataplate for the outdoor unit.

 

[Matthew]

Ugh. At least our AC failed to before if got too hot a few years ago.

Our neighbor has 2 smaller units, one for downstairs and one for upstairs. They seemed OK with it until one compressor failed and the other started to go (about 15-20 years old). Just because they are smaller doesn't mean they are proportionately cheaper.

 

[Clark1961]

2008 Ain't that old.

But the stuff Mr. AC Guy is telling you is riddled with bogosity. R22 is readily available, and I have never heard of a compressor that fails to a recirc mode like that.

Call the home warranty folks, report back.

I deleted my comment about the tech before posting because it wasn't constructive.

There are some simple things Ted could do and the tech should have done to tell him what the system is doing. The first is to check the system pressure and operating temperatures. Also need to check for leaks. AC is simple, a pressure gauge and thermometer get you pretty far. Then ya just call the tech and tell'em what ya need...

 

[Ted]

I deleted my comment about the tech before posting because it wasn't constructive.

There are some simple things Ted could do and the tech should have done to tell him what the system is doing. The first is to check the system pressure and operating temperatures. Also need to check for leaks. AC is simple, a pressure gauge and thermometer get you pretty far. Then ya just call the tech and tell'em what ya need...

He did check the temps and pressures initially when he came and it was working (since it works intermittently). Said the temps and pressures were good once he added a pound of freon (it was a hair low). I noticed no observable change in behavior.

 

[Clark1961]

He did check the temps and pressures initially when he came and it was working (since it works intermittently). Said the temps and pressures were good once he added a pound of freon (it was a hair low). I noticed no observable change in behavior.

I wonder where that pound of freon went?

It's been a long time since I worked on cooling systems. Leaks were rare. Contamination much more common. I'll see if I can dig up some numbers for R22 system.

 

[GlennAB1]

Over the years I've fixed my own A/C a few times. Twice, it's been the start/run capacitor, once it was the fan shaft/bearing not allowing the motor to run, and once it was the outside unit heat exchanger clogged up with dust and grass clippings.

 

[Ted]

Over the years I've fixed my own A/C a few times. Twice, it's been the start/run capacitor, once it was the fan shaft/bearing not allowing the motor to run, and once it was the outside unit heat exchanger clogged up with dust and grass clippings.

I'd thought about the outside heat exchanger being clogged as well. It's remarkably clean, fortunately (or not). It also seems to be doing its job very well. The high side isn't very hot when it gets back to the unit in the basement, so all that heat is being dissipated outside. The low side line is cold (when it's running) as it should be.

 

[Clark1961]

Everything you wanted to know about R-22 but were afraid to ask. See attached files.

 

[denverpilot]

I'm a bit skeptical too. Why would it "trip a breaker" internally if it wasn't having some sort of over current condition? And if it is, why?

I suspect there's a valve in there since it's a heat pump also to switch from
condenser to evaporator and I'm smelling a tech that doesn't know how or doesn't want to troubleshoot the valves.

 

[denverpilot]

Oh PS: my HVAC guy has no trouble at all getting R-22. He's required like all refrigerants to completely evac the system and pressurize with nitrogen to check for leaks, and then recharge, but R-22 is readily available.

 

[Ted]

The issue isn't the R-22, it's the parts for R-22 system (per his explanation).

So, I got home and took a look around the HVAC in the basement and outside. Found a few things.

1) This is a 13 SEER unit, so pretty inefficient. Probably why I think it uses more electricity than it feels like it should

2) There's a vent in the return duct in the basement (about the size of a floor vent) that was closed. I opened it up, and it sure did suck a bunch of air in.

I turned the AC on when I got home (4 hours ago) and it's been working fine since, and gotten the house down colder than it has the past few nights, and it's still getting things colder and working. I'm wondering if it wasn't a return airflow issue that was causing the evaporator to freeze up, and then tripping the compressor.

We'll see how it does. The house is getting down to the temperature where it would be expected to freeze up if it does. Tomorrow is going to be a high of 99. I'll be kinda annoyed if I ended up buying this wall unit AC and it ended up getting used for one day and not being necessary, but that just means I'll have to figure out another use for it.

 

[SCCutler]

When you need a new AC, you'll want to get an efficient one, but the 2008 13 SEER Lennox is not - should not be - "obsolete," yet, and parts are readily available, except to an AC guy who talks out of his azz to sell you a new unit. When you decide to buy a new system, trade with someone else.

 

[Matthew]

Do you think there's restricted return air flow, somehow, that causes the evaporator coil to ice over? Opening up that vent seemed to make a difference.

 

[Ted]

Do you think there's restricted return air flow, somehow, that causes the evaporator coil to ice over? Opening up that vent seemed to make a difference.

He had not claimed that the evaporator was icing over. However, to be fair, by the time he showed up it likely wasn't iced over. Per his description of the breaker for this compressor, once it trips the compressor work again until it cools way down. Well, if given a few hours (which is about what it was), the evaporator will probably melt off, but the compressor won't have cooled off unless it was shut off. All evidence gone by then.

So, given what I understand about the failure mode, I could see the following order of events.

1) Evaporator ices over due to lack of airflow
2) Compressor overheats since there's no airflow over the evaporator, breaker trips
3) Because of the compressor design, the compressor continues to run. The thermostats say the AC needs to stay on, so it stays on
4) Without any cold freon going through the evaporator, the ice melts off the evaporator, leaving no evidence

It's a logical progression. We'll see if it holds true overnight.

 

[GlennAB1]

Awesome! Hope that's all it was.

 

[SCCutler]

Awesome! Hope that's all it was.

Me, too.

Have never heard of a compressor which, when it trips on overheat, keeps running. It simply makes no sense, at all. Still think he's on the Fleece Ted and Laurie campaign.

Not unusual at all for the fan to continue running, even when the compressor overheat is tripped. But a compressor that trips to some recirculate mode?

 

[Ted]

Me, too.

Have never heard of a compressor which, when it trips on overheat, keeps running. It simply makes no sense, at all. Still think he's on the Fleece Ted and Laurie campaign.

Not unusual at all for the fan to continue running, even when the compressor overheat is tripped. But a compressor that trips to some recirculate mode?

It seems like a horrible design that makes no sense. However, the diagnosis does match the symptoms exactly (and this was the diagnosis provided without giving him full information on what happened), so it's hard to say. Even though I did automotive AC professionally and can tell you a good bit about that, I've not done house AC before.

The system seemed to have made it through the night. This morning when we woke up, the house was at the appropriate temperautres, and the system was off. Today's going to be in the 90s, so I think we'll find out pretty quickly if that was the problem. If so, I'll be out $500 (the initial call out and the window mount AC that I will have then used for one day...), but that beats what I would've paid for a new unit.

That said, I'm highly unimpressed if he didn't notice that right off the bat as something obvious to check.

So, assuming this is fixed, I have a 5000 BTU window mount AC, only used once, to figure out what to do with.

 

[Skip Miller]

2) There's a vent in the return duct in the basement (about the size of a floor vent) that was closed. I opened it up, and it sure did suck a bunch of air in.

Check the status of the return air vents upstairs. They may have been closed/sealed off. A properly designed system has return air ducts upstairs as well, so that if you close a bedroom door, for example, the a/c will still function in the closed off room.

But discovering the high suckage at the downstairs vent is a good find. Normally the supply side needs to be balanced so that the cool air flow is balanced room to room and floor to floor. You need to do the same with the return supply although balancing the suckage is not as important.

Suckage is now an aviation term. After all, we have suckage gauges in the cockpit, right?

-Skip

 

[Matthew]

I used to have some decent referrals for A/C guys in the area. Anymore, places are more interested in selling new than troubleshooting old. With A/C being more complicated than simply checking some pressures, you do have to consider airflow volumes both in and out, and I think those "system" things are over some guys' heads.

 

[Ted]

Check the status of the return air vents upstairs. They may have been closed/sealed off. A properly designed system has return air ducts upstairs as well, so that if you close a bedroom door, for example, the a/c will still function in the closed off room.

But discovering the high suckage at the downstairs vent is a good find. Normally the supply side needs to be balanced so that the cool air flow is balanced room to room and floor to floor. You need to do the same with the return supply although balancing the suckage is not as important.

Suckage is now an aviation term. After all, we have suckage gauges in the cockpit, right?

I'll give another look-see around the upstairs return vents, but I'm pretty certain that all of them are fine. Good thought.

I used to have some decent referrals for A/C guys in the area. Anymore, places are more interested in selling new than troubleshooting old. With A/C being more complicated than simply checking some pressures, you do have to consider airflow volumes both in and out, and I think those "system" things are over some guys' heads.

I've gotten that impression as well. It seems that technology in general has continued to head that direction. Just take a look at how complex cars have become. My wife's BMW has more computers than I can count, and some of the failure modes on it get to be extremely bizarre.

Automotive AC is more complex in some ways, simpler in others. You don't turn the fan on and off, but the compressor kicks on and off to prevent the evaporator from freezing up. Basically tries to keep its temperature around 35F. Home AC seems to not do that, and then just rely on having enough airflow to keep the evaporator from freezing.

 

[Matthew]

We were looking into adding extra attic insulation and called a "home environment specialist" or whatever his title was. Recommended by our roofer, he worked for an insulation company. He first went around the house to ensure all the HVAC vents, ducts, returns, and anything else was working properly. His reason: no sense in adding insulation if the HVAC isn't working right. He had a small non-toxic smoke pencil that he wanded around the house, looking for drafts. He showed me lots of areas to fix. We have ceiling vents in the upstairs - they had gaps around them that allowed air to transfer around them into and out of the attic. The recessed light fixtures in the upstairs ceilings also allowed air infiltration. A whole lot of aluminum tape solved that. The downstairs vents are floor mounted but they also let air in and out of the unfinished basement below. None of the ductwork in my house was sealed at the seams, so I went all through everything I could access. He gave me some other tips, too. Eventually I probably closed off the equivalent of 2 square feet of open space on the return ducts, the out bound ducts were already pretty tight. There's still a draw somewhere that I can't find. When I turn on the HVAC fan, and stand next to the basement door and crack it open, there is a negative pressure in the basement that indicates somewhere there is a leak in the return system - I just can't find it. The guy also took his needle nose pliers and bent the vanes on my vents to direct air into the room instead of along the walls. After all this he gave me a quote on the insulation.

It took me a few days to seal everything up and make all the adjustments he suggested, and I could tell the difference in airflow and A/C balance through the house.

Also, I removed the covers from all the cold air returns and inspected inside the walls for any obstructions or anything else that didn't look right. I found a lot of construction debris (nails, sawdust, other) that I cleaned out, but that wasn't really enough to affect airflow.

 

[Caramon13]

We just replaced the A/C in our home too, with a 16 SEER Daikin unit. The one we had was the builder's special from when the home was built in 2005, so it really hung in there. Especially in FL that's amazing.

Got a 12 year warranty with it too, which is unusual, but awesome. The A/C failing is such an amazing inconvenience during the year, but can be deadly down here in the summer.

Hope you got it sorted out!

 

[GlennAB1]

So, assuming this is fixed, I have a 5000 BTU window mount AC, only used once, to figure out what to do with.

I have family that have been through a similar scenario. They have two window AC units that they store and have been able to lend to friends and family when they've needed them.

 

[Ted]

I have family that have been through a similar scenario. They have two window AC units that they store and have been able to lend to friends and family when they've needed them.

That's more or less what I'm leaning towards at this point. And I'll probably come up with temporary uses for it here and there.

 

[timwinters]

I don't know how I missed this Ted, but I did. Just a couple of quick thoughts:

1) What Clark and Spike said. The only thing I'd add that I didn't see mentioned is that if you go back with one big unit then it'd be wise to have a multi stage compressor to go with that variable speed fan. Scroll compressors were the going thing when I installed new units in my house a few years ago and are pretty much infinitely variable.

2) You don't need return air in every room. Return air path is accomplished in many homes by simply undercutting the doors about an inch or so. That affords 30 sq. in. and that's about the same as a 6x10 RA grill assuming it has 50% free area.

I have a unit upstairs and down. My house has a fairly open floor plan and the downstairs unit almost never runs in the summer. My upstairs never runs in the winter. In fact, when I replaced my units about 4 years ago I didn't even put heat in the upstairs unit. It's cooling only.

AS an aside, if I ever build again, I'm going with mini-splits. Good commercial mini-splits, not the cheap residential brands. Some commercial models allow you to run multiple indoor units off of one outdoor unit and the great part about this is that if one room needs heat when another need cool, then the outside compressor might not even need to kick on. The indoor units can just swap heat through the refrigerant. And all the ductwork and a lot of other hassles are eliminated.

 

[Theboys]

In my Florida house I have two systems. One for the bedroom wing that is 4tons and one for the living entertainment wing that is 5 tons. I love it and keep them at separate temps, as I like to sleep cooler. When I was looking to replace mine I had bids as high as 22000 and several in between the one I picked, which was 10000 to replace everything. Went with higher end system and don't regret at all. My new system blows so much air you can feel a breeze on your face and cools whole house down in maybe a hour. My electric bill was chopped almost in half and I figure if one ever go's out I can be comfortable anyway. I would probably never have a house again with single system.

 

[Ted]

Good info, thanks to all.

So far it looks like opening that return duct in the basement fixed the issue. The system has been operating perfectly since last night with no problems.

However, I'm pretty sure that there are some leaks within the upstairs vents given the ridiculously low airflow up there. So, I may do some investigating with aluminum tape to see what I can find.

Now I have this window unit... we're thinking we might add a window in the garage (I'd like natural light in there anyway) and then could do the window unit with that.

 

[Matthew]

Interesting about that extra airflow from the basement return air and how that seems to have solved the problem. Do you have any outlet vents down there to balance out the return?

My unfinished basement has a single outlet, probably code, but no return other that whatever leaks in the system cause a low-pressure in the basement when the unit runs (and I tape around the air filter, too). If I can ever find that and seal it off, I wonder if the pressures in the whole circuit would add extra airflow to the living areas (2-story).

 

[Ted]

There's one outlet vent in the basement, but I keep it closed. It's normally cooler down there anyway in the summer. In the winter, we bring blankets. It's unfinished for now but we keep the TV down there. The airflow down there to balance the return I'm guessing comes from the leakage around the basement door (it's about 1" above the floor) and leakage in the ducts.

Given that it's all worked well today, though, I think we'll call off spending any large amounts of money.

 

[vkhosid]

There's one outlet vent in the basement, but I keep it closed. It's normally cooler down there anyway in the summer. In the winter, we bring blankets. It's unfinished for now but we keep the TV down there. The airflow down there to balance the return I'm guessing comes from the leakage around the basement door (it's about 1" above the floor) and leakage in the ducts.

Given that it's all worked well today, though, I think we'll call off spending any large amounts of money.

Why do you hate capitalism?