What Causes Compressor Leads to Burn Off of Terminals?

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Ken Hall wrote:

one thing to do with HVAC besides sit at the computer and post non stop bullshit to a HVAC newsgroup.
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On Sat, 30 Sep 2006 11:25:00 -0500, Ken Hall

We know its baffling to you. That's why you're here. Trust us. We know what we are talking about. Now go get a new thermostat. You might want to also install one of those new ReverseFlow@ductboosters while you're at it.

Clack? Oh shit! Never mind. You need to replace your system immediately. Bubba
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He was actually giving away a possible cause of the problem. What sometimes happens is that the stat starts the compressor - that's the "one solid clack" you hear. Now, the system comes up to normal operating pressure. The thermostat might have a problem (it might not even be the stat's fault - think door slamming near a mercury stat) where it momentarily allows the contactor for the compressor to open. Now it closes the contactor again. We've got head pressure, so you wind up with a locked rotor condition. If the compressor is running, it draws - oh... something less than the rating of the breaker feeding it. During a start, and while you are in a locked rotor condition, it sits there drawing whatever it feels like - some large multiple of the recommended breaker rating until something gives. That would be one of the thermals, the breaker feeding it, or the wiring to it, or the windings. Something is wrong with this picture. It could very well be the thermostat. The real expensive, good ones are recommended for a good reason - they generally have a parameter that allows the knowledgable installer to control the minimum cycle time.
From what you've said, it's been happening every six months for the past 12 years. That means - to me, anyway - that six months after you had this unit installed, it burned it's first set of leads off. After the second time it happened - and certainly during the 7th, 8th, or 9th year it happened - you should have been asking a few questions about why it keeps happening, and what they plan on doing when the manufacturer's / installer's warranty is over. The wire to that you are trying so hard to re-attach is so badly corroded, and contaminated with Hydrochloric acid from the burned PVC that there is no hope of a permanent repair with the present wire. You need to find someone who knows what they are doing to look at the unit, and assess whether the terminals are too far gone, whether there's an issue with the control system, and whether it's just time to say goodbye to it. That would likely be someone other than who's been out there between 12 and 24 times for the "same" problem.
Somewhere along the line, did they at least suggest replacing the compressor, and you didn't want to pay the labor? When you are messing with those terminals, are you using correct PPE? Remember that there's 50-100 PSI - when it has been off for a while - behind those innocent looking little studs. The glass seals have likely been stressed by the heat, and a nice R-22 / oil injection into your hand might be the most minor thing that could happen. BTW, you could lose fingers / hand later due to gangrene if it lets go, and the conditions are right.
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Thanks for your reply.

This thermostat cost $125 12 years ago. It uses a thermistor not a mercury switch. It has a cut-out timer in it such that if the signal to the a/c unit is lost for any reason there is a 4 minute delay before it will call for cooling again. Also, there is a similar, redundant, cut-out timer in the condenser unit that won't let the compressor start again after a power dropout for about 3 minutes. I never see this one in action because the delay in the thermostat is longer.

This lead is the Term-Loc lead that was installed about 6 weeks ago. They only burn back about 3-4 inches from the compressor terminals. I cut this off when I redo them.

No.
Thanks for the warning.
-- Ken
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replying to Ken Hall, Big pemp in wrote: Yes I know when someone said t-stat was causing that issue .... I usually well change the contactor and the cap just saying
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"Big pemp in" wrote in message
replying to Ken Hall, Big pemp in wrote: Yes I know when someone said t-stat was causing that issue .... I usually well change the contactor and the cap just saying
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Ken Udarrell have gave you good explanation I had few of those myself but so far none repeated, these is what I do when you replacing terminal (stay-cons) first make sure you wires are rated for current require, crimping wire some time it is not enough you may need to solder in and then make sure that terminal fits on tight you can also squeeze in terminal part that goes on to log before it is pushed on, after that is complete you can add small glob of silicon compound on to each terminal preventing getting moisture on and helping keep rust off. Good luck from Dido

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IF the super boost was correctly installed, it *might* help, so would correctly wiring that replacement run capacitor(it *IS* the correct value, isn't it?)...however, the contactor looks like it has been arced across and it should probably be replaced and the original problem corrected. Unless I miss my guess, its a Goodman unit that has been repeatedly hacked over by the lowest bidder and then screwed with by the owner.
Its pointless to ask what kind of metering device does the system have?? When the compressor *IS* running, what is the SST and superheat?? What is the LLP and subcooling?? What is the amp draw on the compressor??
Best you can hope for is to call a *competent*(not cheapest), licensed, insured, professionally trained, HVAC technician to come straighten out your mess.
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Thanks for your reply.
wrote:

It's a Copeland compressor in an Amana condenser unit.
The "hacking" I've done is: changed the contactor once installing inadequate connectors (same as the original installer used) when they burned off shortly thereafter installing the Term-Loc wires -- at your suggestion if I recall correctly installing the inadequate connectors twice more in the last couple of weeks after the Term-Loc wire burned off.
The last two events prompting me to post this question.

This depends on the conditions. The last time I made measurements these were the conditions and results:
indoor temp         74     outdoor temp        95      low side             pressure        67 saturation temp    38 suction line temp    45 superheat        7 superheat should be    7 per manufacture's pamphlet

18 amps -- about right for the conditions per manufacturer's pamphlet
-- Ken
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Subcooling *maybe* with a TXV but not superheat.

Part of your problem is that the system is overcharged and the compressor is sweating and most probably causing the terminals to be wet all the time causing high resistance connections. With a 67 PSI SP, I would look for an SST of approximately 58 degrees with a fixed oriface(piston) metering device. Recover the refrigerant overcharge, and try again.
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wrote:

You're wrong. I have the pamphlet that came with the unit in front of me.
-- Ken
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Ken Hall wrote:

wrong! If the compressor is sweating too much it can create problems with the terminals. Superheat does not mean anything if the airflow is too low or there is an insufficient heatload going through the evaporator coil.
It could be overcharged, -read the linked page! http://www.udarrell.com/airconditioning-excessive-airflow.html
I have not read all the posts so don't have enough info to make any meaningful assessments! - udarrell
--
Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/airconditioning_eer_ratings_over_seer_ratings_central_systems.html
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wrote:

I said he was wrong about the superheat of 7 not being correct. In effect I said he was wrong in saying *I* was wrong about the superheat. Maybe you want to tell me how I misread the superheat chart I linked to.

I didn't say he was wrong about that.

I don't disagree with that. Some *other* problem making the factory specified superheat meaningless was not the issue. Other problems can cause all kinds of difficulties. The issue was whether the superheat I quoted is what the manufacturer specified, and it is.

Thanks for the link. It seems to deal with systems that are performing below rated capacity. I don't have that complaint.
-- Ken
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On Sat, 30 Sep 2006 23:36:10 -0500, Ken Hall

Ok genius, what's the wet bulb, dry bulb, cfm, return duct size, filter size and tonnage of the system? Yep, thought so.
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On Sat, 30 Sep 2006 20:45:44 -0500, Ken Hall

lmao. he's an expert with a set of gauges!
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I should have added, you're right that the suction line sweats all the way to the compressor. I've attributed that to the fact that it's Houston and Houston has high humidity.
-- Ken
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Ken Hall wrote:

Ken,
I've read all this back and forth and can't really answer your question... except to give you another avenue to look at...
I'm an electrician and NOT a HVAC guy, so take it for what it's worth.
What you describe are classic symptoms of a low voltage condition on startup.
Look at the side of your condensing unit and see what the required current is.... and then compare it to the wire size you have going out there.
Check all of the connections from the breaker, to the disco, to the unit. Clean and re-tighten all of them (with the breaker off, of course). Open/close the disconnect.. and while open inspect the thing.
Does your home have a adequate (in these days meaning at least 200 amp) service?
Did the contractor make the aluminum/copper wire transitions correctly (if applicable)?
Starting current is one heck of a lot than what it takes to run the thing... and I'd surmise that's where the problem is... a low voltage condition on start due to bad feed capacity or poor connections somewhere.
Just my 2 cents worth.
Jake
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On Sat, 30 Sep 2006 21:02:14 -0500, Ken Hall

DOH!
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wrote:

If I'm reading the chart wrong, please explain. Here it is:
http://img86.imageshack.us/img86/3365/superheatua7.gif
-- Ken
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What kind of metering device do you have?? What is your LLP and LLT??
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