What parts to salvage from a old A/C unit

The compressor, for overload testing circuit breakers...

Other than the contactor and control transformer I think that's about it. There really isn't all that much in an A/C system.

Pete C.

According to Ignoramus1064 :

And -- if it were not dead -- the compressor as a source of compressed air, or as a vacuum pump. :-)

Keep the contactor -- for when you need to switch something high-powered.

Check out the time delay switch module. It should work nicely at low AC voltages, such as the 24VAC which your AC was using. Essentially, it first produces close to an open circuit between the terminals until the time has elapsed with voltage across it, after which it switches to low impedance and keeps current to the contactor coil, at least until the power is interrupted for a second or so.

There must be some use which you can find for it -- or keep it as a replacement for the one in the new unit when that fails -- assuming that it does still work. If the contactor closes as soon as your wife switches on the breaker, it may have indeed failed. Though it is probably running from a different breaker -- 120 VAC to the rest of the system.

You might want to salvage the valves from the old compressor.

And the outside coil could probably also be used as a cooler for the air compressor.

Enjoy, DoN.

The contactor is a disgusting POS. 1.5 pole contactor. I have a lot of much better contactors, although none is 24vac, but that's OK, better

24vac ones cost next to nothing.

The control transformer, etc will remain as part of the furnace and controller that I will keep.

i

Copper is at $3.50/lb today, aluminum $1.20. You may be better off at the recycler's.

Ok, so you mostly have scrap metal.

Pete C.

I don't think his unit has (had) the optional time delay module which is probably why it died from the momentary power hits.

Pete C.

Doesn't appear to be any "magic smoke" left to save.

Make sure the new condensing unit has a 3-minute "Delay On Break" timer inline with the compressor contactor coil for just such occurrences. The first time the unit starts immediately, but once the

24V line drops out the module goes open and will not allow a restart till the delay period passes.

Some of the fancier furnaces build that function into the computer control board inside. Even with that, adding one can't hurt.

And if it doesn't come with a high-limit pressure switch on the high side and a low-limit pressure switch on the low side, take the initiative and add them. The cheap 'Builder Model' units skip these two switches to save $20 wholesale - when they're putting up tract houses, $20 x 500 houses, and suddenly you're talking real money.

The high limit will shut down the compressor on a bad condenser fan motor before you blow a refrigerant line from high head pressure, and the low switch will cut the compressor off on low refrigerant charge - hopefully before the compressor overheats.

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Bruce, I will absolutely definitely do that! (as I do not trust other timers any more). I will ask our HVAC guy if the Trane unit has it, if not, I will ask him to put one in, and, worst case, I can always install one myself.

Just to clarify, an example of such relay could be ebay item

7590695541, right?

Our HVAC company will install a new thermostat with this function built in, but, I think, it does not properly save me from power sags.

Bruce, I am going to have a Trane XL15i outside unit, does it have these features?

See

I checked out their list and did not find information about these switches. Should I mention it to our HVAC guy?

I want, indeed, this unit to be protected from typical causes of breakdowns.

Makes sense. I will spend money, if possible, to get these switches installed. They should be installed prior to system charge, right?

i

go for jeans and a red shirt tomorrow.

That's the MARS one. Their "Buy It NOW" looks like full list price and I didn't even look at S&H fees, buy it locally or bid the $6 on it. Which raises the question of why they're selling supply house stuff like that on E-Bay in the first place...

(And don't cut the white wire loop unless you are using it on 240V directly! RTFM.)

If you have a newer furnace with a processor driven control board (little green blinking status LEDs and a 'Troubleshooting Chart' to interpret them) it probably has the time delay in it, and the break delay will only confuse it that the contactor coil is open, or one of the safeties has tripped open.

Gee, searched the Trane site and didn't find any mention - but that entire website is aimed at the consumer, everything we build is rock solid, all sunshine and roses, blow smoke up your ass...

They don't want to mention that the low-end units are not protected but the premium models are - that would get the retail customers annoyed when they find out just how cheap the low-SEER "Builder Model" that came with their new house is (and we'll buy Carrier next time).

When they're putting in your new unit, they should be able to open the access door on the condensing unit and point the two switches out. And they can be added later, if there are 1/4" Flare test ports inside the condensing unit to connect them.

They make Tee adapters with a male and two female test ports, and the switch mounts to one of the two female ports on the adapter. Hook them all in series with the contactor coil. They are light enough that no brackets are needed. (Robertshaw) Uniline and (Texas Instruments) Klixon make them.

The switches look like the oil pressure switch on a car. 1/4" male Flare fitting on one end, two leads or QC connectors. Reset button on the end if it's a manual reset - optional for the high-side switch, so it will cut-off and stay cut if the condenser fan motor fails.

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Bruce, yes, the price is not very attractive, I just want to see if that relay is what I need, basically. That's what I would like to know.

Oh, I see.

I am concerned about, momentary power outages (1 second blackout). The furnace may not notice it, but the A/C would get in trouble if the timer does not properly work.

Yeah.

Would that 15i be a protected one?

These are relief switches, is that what you are talking about? Just want to be clear.

thanks Bruce. I want to learn about this stuff and get something "well made".

i

Trust me, the computer on the control board will notice the power dropout - it runs off the 120V to 24V transformer itself, and has no capacitor 'carryover' on it's own power.

When the controller computer crashes from the power drop and then reboots when the power returns, it will NOT try to restart anything (heat or cool) until it goes through a time delay, and it will run the furnace section forced draft blower through a combustion chamber purge cycle for 30 seconds just in case it was running on a call for heat when the power dropped out.

I don't know. Read this part again:

No, they are pressure switches to cut off the compressor by opening the power to the contactor coil when the system goes out of whack, hopefully before something gets wrecked.

Most residential AC systems do not have a relief valve on the refrigerant system, because the valves have a tendency to develop leaks over time. If anything, they would put a rupture-disc type relief valve (like on an oxygen cylinder) that vents on a severe system overpressure.

"Well Made Residential AC Equipment" is an oxymoron that ranks right up there with "Military Intelligence".

Even "Commercial/Industrial Grade" isn't a reliable way to do it. The highest price points on mass-produced equipment will get you good quality, but 99% of the people out there would balk at the price of what I'd call a really 'Well Made' system.

You can get a really good, really efficient, and really foolproof custom system built for you from individual components - but it will cost you a ton and a half. And any maintenance or repairs will be easier - but will require someone who really understands the entire system, because there won't be an Instruction Manual for this one.

That knocks many of the "first-line" techs right out of the box, the ones at the "Duhhhh... Go to the freezer, get the box..." level of experience intelligence and training. You'll need to pry his Boss (the guy with 30 years of field experience) out from behind his nice comfy desk to come look at your system.

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