Weekend Adventures in HVAC Repair

"Aremmes" (aremmes) 07/11/2020 at 19:50 • Filed to: HVAClopnik

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Last evening as I was winding down from WFH’ing I noticed a rattling noise coming from the direction of my neighbor’s house. I didn’t think much of it, other than assuming that said neighbor had set up some kind of machinery that converts electrical energy into rattling noises, and who am I to judge how said neighbor wishes to spend his electricity budget. As it didn’t anyone in the house, I left it at that.

Of course I didn’t leave it at that, though. Why do you think I’m writing this post in the first place? The rattling noise kept rattling into the night and lightly intruding into my Oppo-reading activity, so I walked out to see if I could find the source of that noise. As I turned the corner I began to notice that the sound was coming not from the property of my neighbor with the three fifth-gen Altimas of different colors, but from my house’s air conditioning condenser unit. And it wasn’t just a noise like that of a bad motor bearing, but a full-on maraca band that I had never heard before. Not Good®.

Hold up. It’s not hot inside the house, why is the outside unit running? Time to check the thermostat. Three full degrees below the programmed threshold. Bugger. Maybe my thermostat is bad? Shut it off. No change. Pull it from the wall. No change. Pull the batteries, put them back in, reinstall the thermostat. No change. Go downstairs and check the heat exchanger. It’s not running. This. Is. Sparta Bad. I can already feel my sphincter clenching in anticipation of the HVAC repair bill.

Who drags a condenser unit out to the driveway for repairs? That guy right there.

Thinking that maybe the noise is caused by the compressor hitting some pressure threshold due to the heat exchanger not heating the gas on the low pressure side, I switched the air handler from Auto to On and checked the vents, confirming cold air coming out. About a minute later, the rattling subsided, although the outside unit was still running. The temperature in the thermostat was still lower than the set point, though. Hhmmm. So I turned off the fan and cut the power to the outside unit at the outside switch and the breaker panel and sat down to investigate (read: hit the Googles). I quickly found an answer, pointing to the contactor welding itself closed and preventing the compressor motor from shutting off when the thermostat has de-energized its coil. Ooooh .

Now that I had a something to try, I left it powered off overnight so I could look further into it today. After taking the wrong brake parts to FexEx to RMA them back to RockAuto, I took a few tools out and went to the outside unit to check it out. Just four sheet-metal screws held the side panel in place, which when removed revealed the prime suspect in plain sight.

That’s some old-ass shit.

After taking a few pictures that had nothing to do with planning to post to Oppo I swear to dog, I pulled the wires, unscrewed it from the frame, and then started to look for a hardware store that may have these in stock. I found a few places, but most close on Saturdays. One was open, and a phone call revealed that they have many types in stock. It’s a 21-mile drive there across twisty mountain roads — yay Miata driving time. They close at 4pm, though, and it’s 2pm when I called the store to inquire. Shit, gotta move.

So I got there with the old contactor in hand and they ask me what type it is. Sure, it’s a 40-amp double-pole. What coil voltage, they ask. Record scratch noises. Apparently I needed to know this ahead of time or test it in place to know what voltage the thermostat sends to energize the coil. Sure, I could do that, but I ate 45 minutes getting there, and there was no way that I’d be able to drive back home, test the voltage, and drive back before they close for the day. Meanwhile the clouds parted and the house has begun to resemble a lime kiln. They also don’t open on Sundays. Helpful fellow there suggested to buy a bunch of them and install the one that matches. They’re cheap enough, so $85 later I had three contactors and a receipt.

Back home, I hooked the multimeter up to the thermostat signal line, turned the thermostat on, and got a 24 VAC reading. Nice. So I started to hook one of the new contactors up according to the pictures that I took, right up until one of the spade connectors for the wires leading to the coil decided that 30 years is a long enough life and decided to break and fall off. Shit, what to do now. I remembered that I had some leftover spade connectors in the garage from when I was doing electrical work in the boat I sold last year, so I walked over there and dug around. Ten minutes later I had two female spade connectors of the right size, which I crimped onto the newly bare wire.

All wired up, I buttoned everything back up and went to do a smoke test. Power to the air handler was on: check. Flipped the breaker to the outside unit, no smoke: check. Outside switch to on, no smoke, compressor doesn’t start immediately: check. Set the thermostat to cool, compressor starts and doesn’t release the magic smoke: check. Put a hand on a vent and confirm cool air: check.

YYYYAAAAAASSSSSSSSSSSSSSSSS.

With that done, I sat down for a beer and contemplate how much beer I can buy with the money I saved not having to call an HVAC technician. It's a lot of beer.

MM54 > Aremmes 07/11/2020 at 20:02

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Nice work! Welded contact s are definitely a thing but I’m surprised to see one on something so relatively-light-duty. Good thing you noticed it was a problem, probably saved you burning out the motor/compressor from ignoring it all night.

ranwhenparked > Aremmes 07/11/2020 at 20:06

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My system is a good 37 years old at this point and is running purely out of habit. Pumps out almost as much Freon as it does cold air, and has a condenser coil that looks like the chassis of one of Dave Tracy's Jeeps. I've decided the next time I call an hvac tech will be when it fails completely and won't come back on no matter what

Aremmes > MM54 07/11/2020 at 20:23

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Thanks. I count myself lucky this time, but I'll still keep an eye on it and see if performance decreases, and call a tech for a checkup if so. But for now, the house is back to comfy.

Aremmes > ranwhenparked 07/11/2020 at 20:27

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Mine is not much older at 30 years. In fact, the old contactor is date-marked “07/90". The components don’t look terrible, so I think I can maybe get another 10 years out of it. The one in my previous house was 42 years old and still running strong when I moved out.

VincentMalamute-Kim > Aremmes 07/11/2020 at 20:39

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Good work.  But what was making all the noise?  Surely just the compressor not turning off wouldn’t do that?

BrianGriffin thinks “reliable” is just a state of mind > Aremmes 07/11/2020 at 21:00

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My system  is 30+ years old and I live in fear of this one day. Probably tomorrow 

Aremmes > VincentMalamute-Kim 07/11/2020 at 21:11

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My guess is there's a pressure relief valve was opening due to a frozen evaporator.

Roadkilled > Aremmes 07/11/2020 at 21:13

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I’m not surprised a contactor had problems after 30 years. Let’s assume that your system is used 100 days a year, and it cycles on and off twice an hour. That would be 50 operations a day and 5000 in a year. 30 years of operation would be 150,000 cycles, which is a pretty good life for a contactor. 

jminer > Aremmes 07/11/2020 at 21:16

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Way to go!

This is always an especially satisfying repair, in the last couple years I’ve replaced my air handler motor, couple capacitors, condenser motor and an igniter and they’ve always made me feel like a million bucks when done.

ranwhenparked > Aremmes 07/11/2020 at 21:25

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I think things were built better then. A couple years ago, I looked at a house from 1934 that still had its original furnace, apparently in working order with a recent service tag/efficiency audit. Only 65% efficient, but, still, you can buy a lot of natural gas for what a new furnace costs every 15-20 years.

RacinBob > Aremmes 07/11/2020 at 21:28

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Actually, I think because the compressor was on but the air handler was off, what you were hearing is liquid refrigerant that couldn’t be boiled flooding back to the compressor causing it to slug as it is trying to compress a liquid. That is why it stopped doing it when you turned the air handler back on.

As for the contactor. It is a single pole single throw contactor.220 volt power is two hot 110v wires across the motor . Y ou only need to switch one leg of 220 volt as if you open one leg, you open the circuit. I had not though about that once and worked on a compressor without opening the breaker and touched the other unswitched leg. It educated me in a way I won’t forget.

If you look at the picture. The red side is the contactor. You notice the arrow showing the bar you can push to manually make the contactor close. Notice it is down when I assume it is off, yes it appears to be welded on.

The blue line is the other 110 v circuit. As you can see, it is just a copper bar and not a contactor. A double pole would have a parallel contact instead of the bar. 

Snuze: Needs another Swede > Aremmes 07/11/2020 at 21:37

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Thats almost as old as the Jankwagon!!!

Eric @ opposite-lock.com > ranwhenparked 07/11/2020 at 21:37

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How do you get that long out of them?! Ours is like 12-13 years old and the HVAC guy said we’d be lucky to make it another 5 before it needs replacement. It looks decent, aside from some hardcore sun baking due to the side of the house it is on.

Snuze: Needs another Swede > Aremmes 07/11/2020 at 21:40

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Well done!  I get an occasional rattling in my system, but so far its always been small rodent carcasses from some damn bird that keeps dropping them in there!

smobgirl > ranwhenparked 07/11/2020 at 21:49

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I just pulled the original furnace in my house a couple years ago. 

Aremmes > RacinBob 07/11/2020 at 22:06

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Thanks for the detailed analysis. Your explanation of the source of the noise makes sense. I figured it had to do with trying to push gas where it can’t, but I don’t know enough about thede things to give more than just a guess.

As for the contactor, I assumed it was a DPST precisely because it's switching 240V split-phase. It doesn't make sense to me that half the motor should be live at all times.

Aremmes > Snuze: Needs another Swede 07/11/2020 at 22:14

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I would have been lucky if I just had to clean up animal or plant matter that hit the fan blades. :D

ranwhenparked > Eric @ opposite-lock.com 07/11/2020 at 22:19

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I have no freaking clue. This house has the original oil furnace and Magic Chef air conditioning from 1983. The furnace was serviced last year and is apparently in perfect shape, the external a/c compressor unit is almost scrap metal - the bearings are shot and the condenser coil is corroded to paper thin Swiss cheese, but it somehow still runs and cools. I had it recharged with Freon last year, but the tech basically condemned it, could fail any time.

When I moved in in 2018, I called an HVAC service that a friend recommended to schedule a service appointment, and when I gave my address , the guy told me it would be $12,000 - he looked at it a year or two earlier with the previous owner and recommended total replacement of heat and air, wouldn’t even come out and look at it again.

One thing that is going on with furnaces is that the modern, super efficient burners have to be made with thinner metal that has a much shorter service life than the thick, heavy, cast iron used in older furnaces. You get lower operating costs, but they only last 1/3-1/5 as long. For a/c systems, I think its just cheaper components and planned obsolescence. 

Pops > Aremmes 07/12/2020 at 09:25

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While you were at it a split capacitor would have been a good investment. It is the number one failure , in our area , and relatively cheap to replace.

I also clean or replace all terminals relating to a contactor when replacing one. Poor conductivity can shorten the life of a new c ontactor or  capacitor. This can easily be checked by checking for a voltage drop at the contactor.

Eric @ opposite-lock.com > ranwhenparked 07/12/2020 at 17:06

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The A/C compressor units (the equivalent of the one you’ve gone 37 years on) are the thing that go faster, apparently. The furnace is surprisingly long-lived. He said it’s probably at least 10 years from needing replacement, maybe further.

But I don’t get why they can’t just upgrade them. If they’re properly sized and the coolant doesn’t change, there’s no reason to replace the radiator. If the fan still runs properly, no reason to replace it. The compressor is the wear item... My parents have one that is at least 20 years old that is still running fine.

Apparently mine lacks a protective circuit/sensor, so I’ve been thinking of ways to build something out of a Raspberry Pi, some sensors, and some relays to ensure everything is running correctly in the system when it’s running, then turn it off automatically if anything goes off. Years of historic data of how it runs could also inform when components are failing.

Dave > Aremmes 07/12/2020 at 18:02

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The 120 volt side that is shunted live is for a compressor heater circuit that either runs thru the windings of the motor during off cycle, ( or is a belly band wrapped around the base of the compressor) to vaporize any refrigerant that migrates back to the compressor when thermostat is satisfied or unit turned off.

ranwhenparked > Eric @ opposite-lock.com 07/12/2020 at 18:51

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Sometimes you can get away with replacing just the external unit, if you can get one that matches perfectly with the rest of your system, and, as you mentioned, uses the same refrigerant. Would probably compromise your warranty, though. And, in my case, its old enough to still use Freon, so the whole thing would have to be replaced anyway. 

Eric @ opposite-lock.com > ranwhenparked 07/13/2020 at 13:01

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Yeah, you’ll never get another freon one, so you’d need new coils/radiators/tubes . Still, the electrical parts last indefinitely, the main wear items are theoretically easy to replace and the radiators shouldn’t go bad from use even over many decades. The coil mounted in the heater should last essentially forever provided you change your filters (even then, vacuuming them out like once every quarter century shouldn’t damage them).

It’s just the obsession with efficiency for me. This is some of the most industrial equipment in a typical house, so like industrial equipment I feel like you should only replace components of the equipment when they go out, not the entire piece of equipment for the failure of a single component.

ranwhenparked > Eric @ opposite-lock.com 07/13/2020 at 13:48

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Yeah, I hate modern stuff that’s designed to be replaced completely, rather than serviced and repaired. A lot of mechanics are like that now, too. They don’t want to rebuild or refurbish, just bolt the old part, throw it away, bolt the new one on. If a new part isn’t available from their preferred supplier, either they’ll turn you away, or park it out back for a few months while they try to figure out what to do.