Need help diagnosing problem with A/C

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I have a 6-year-old TempStar SmartComfort 2000 A/C unit that's generally behaved well up until this year. But now we're having serious problems and the two techs that have come out have not been able to resolve the issue. I'm not electrically inclined and I don't know much about HVAC in general, so I'm hoping someone might have some advice on this problem.
Basically, the symptoms are these:
* From an off state, I turn on the thermostat to Cool and the compressor starts up. About 20-30 seconds later, the blower on the furnace comes on. The air's good and cold -- no problems so far.
* Anywhere from 10 to 30 seconds later, the compressor and fan click off and then immediately back on. It repeats this 4 or 5 times, speced anywhere from 5 - 30 seconds apart. After that, the compressor/fan shuts down.
* As soon as the compressor stops, the furnace's blower kicks into high gear. It is then impossible to stop the blower by means of the thermostat. Turn it off, turn up the temp, turn it to heat, remove it from the wal, ... the blower keeps going. To turn it off I have to use the switch in the furnace cabinet.
* Now, even though it's off, if I turn the switch in the furnace cabinet back on, the blower comes right back on (compressor/fan still off) and will run indefinitely (as far as I know -- I've let it go for an hour once before shutting it off again).
I end up having to wait anywhere from an hour to a day or more before I find I can turn the switch in the furnace cabinet back on and NOT have the blower start. At that point, I can restart the whole process: turn on the A/C and the compressor comes on, etc.
The two techs that cme out both diagnosed the problem as the compressor overamping. Here's their exact diagnoses:
Tech #1: "Unit is way overamping. Rated at 18.6 amps, amping at 19.8 amps. Overamping due to burned contact points and wrong size fuses."
Tech #2: "While out by condenser running, compressor dropped out. When it reset checked amp drain. Compressor is overamping, will need to replace."
The second tech said the burned contact points and fuse couldn't be the problem and that the entire compressor would have to be replaced. Based on other feedback I've received, the consensus seems to be that neither tech is correct.
Thanks for reading all of that, and thanks for any advice you can give me. I'm scheduling a third tech to come out but would like to have more of a clue before he starts so hopefully I can steer him in the right drection.
Thanks - Ken
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tivolo wrote:

pressure equalizes the control closes the contacts and the condenser cycles back on.

If the contact points are burnt that will cause high resistance that will reduce available voltage & thus spike-up the amps. Voltage times amps = Watts. It may or may not be pulling excessive watts. Voltage should be checked on each side of the contact points to determine any drop. The high amp draw may not be due to the contactor points!

on the overload independent of the condenser fan motor. Pressures may not have equalized enough for the compressor to restart without over amping for too long a time period.
Is the condenser clogged with cottonwood or other debris?

It is probably a simple fix for a good trouble shooting tech. PJM is correct. It appears that, especially the one condemning the compressor "might" be pulling your leg for some quick cash.(?) - udarrell

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Thanks, udarrell --
When the compressor goes off, the fan always goes off as well. The condensor doesn't look clogged with anything -- the fins look very clear of deris inside and out.
One other thing I forgot to mention: sometimes when the compressor shuts off it does so with a very strong "bang" -- it sounds like someone kicked the side of the unit's cabinet. Also, from time to time it will run just fine. For example, it ran for almost two days straight this weekend before finally giving out. Since then, we can get it to run for more than a couple of minutes (and usually less than 1 minute).
Thanks again - Ken
udarrell wrote:

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The furnace blower should come on right away.

The fact that both the compressor and the outdoor fan shut off , plus the fact that your furnace fan is acting up, suggests to me that you may have either a faulty thermostat, or a faulty circuit board on the furnace.

It should be on high speed right from the start, unless it's a Coleman, which for some reason known only to their engineers and God, the default cooling speed used to be medium high.

If, when you remove it from the wall you mean disconnect the wires from it, then you have a faulty circuit board, or faulty t/stat wiring.

Circuit board or t/stat wiring...

So why is the outdoor fan shuting down??? And why is the furnace fan delayed in starting, and running on for hours after shut-down?
Furnace circuit board or thermostat wiring. Is this a Carrier furnace by any chance, with an HK42 circiut board?
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not necessarily.....could have a time delay on evap fan start up gives the system a higher SEER rating
wrote

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A delay on the outdoor unit to allow pressure equalization, but the outdoor unit starting up, and the indoor fan not???? Is that what you mean?? Never heard of it.
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Bob_Loblaw wrote:

Bob,
Controls can (and do) wait to bring on the indoor fan until the evap reaches a setpoint. I've seen this done with both suction line temp and pressure feedback from a ETXV.
It'll push efficiencies real hard on VS indoor fan motors... where we can 'modulate' the airflow to maintain a constant temp. range.
Is it possible that the evap. coil is so cold (or hot) that the control is telling the ID fan to run continuous? I don't understand the logic behind that... but it may very well be built into a board somewhere.
Figure this: Cooling call. The condenser is SUPPOSED TO BE running. Indoor board sees the evap. pressures out of tolerance... or the evap. temps. high. Would a programmer somewhere have decided the ID fan should run in these conditions?
I wonder....
Jake
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What system utilizes this?

Never seen or heard of an indoor fan deliberately not running while the A/C is powered.

Where would you find a sensor that monitors the surface temp of the coil on a residential application?

Honestly, if it is, it's new to me.

What's connected to the evap that's monitoring the pressures?? This doen't make any sense to me, Jake.
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I would agree with you on the time delay on start up but the blower staying on 24/7. This sounds crazy but it also sounds like a limit on the furnace has opened and the blower locks on low speed for safety purposes.
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A limit automatically kicks a fan to high speed when it's tripped.
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Thanks for the reponse.
Ever since the unit was installed there's been a 30 second delay from when the compressor started to when the blower starts. The same is done for the heating -- the furnace starts and heats up for 30 seconds before the blower starts, so I think this is normal operation. Similarly, the blower usually stays on for 30 seconds or so after the A/C compressor shuts off.
I've attempted to eliminate the thermostat from the equation by removing the control portion from the wall so it can no longer send signals to the furnace. With the themostat removed, I then put a jumper between the Y and RH posts. Using this technique I can reproduce the same cycle of events as when the t/stat was on the wall. And, even once I remove the jumper, the blower continues indefinitely.
I have checked the connections of the t/stat wires to the furnace circuit board and that all looked fine (which is not to say the circuit board isn't bad) -- just wanted to eliminate the possibility that a loose wire was causing the issue.
Thanks again - Ken
Bob_Loblaw wrote:

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If I were you I would put down the tools and walk away. Call some company that has a NATE Certified Tech and have them out.
You stated you jumped from RH to Y post? You jumped from power for the Heat to the Cooling connection. Now if you jumped from R to Y, I would not have thought twice.
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In my thermostat there is an RH and an RC, which are wired together, so I just picked one. But the point of your post is a valid one -- I have a tech on the way, but not until Aug 7 (because of the heat wave).
Ken
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Aug. 7th!!?? Where do you live? Christ! I could walk to your house by then,regardless of where you live!
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24 volts is 24 volts. The system doesn't care where it comes from. But jumpering only the Y won't bring the fan on.
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When I jumpered the Y only, the condensor kicked on and 30 seconds later the blower came on. The sub-base doesn't appear to be anything more than wire connected to a set of contacts for the pins from the t/stat.
When it gets into its final state of blower at high speed with the condensor off, removing the jumper has no effect -- blower keeps going. One other interesting note: in the times when the condensor has been running, I've never heard the blower running at high speed. It only gets to that level when the condensor goes out.
Ken
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True, but when he wrote RH it just should me he didn't know what he was doing and didn't want him to do any thing that might damage his system.
Anyway he got retail help coming.
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Overamping can be account of dirty condensor, or overcharge (too much freon). Might be tripping off, with a high pressure safety. Or the current sensing protector on the compressor. Needs someone to sit and watch it while it does its "routine". Find out what the problem really is. Hook up gages and ammeter, see what the thing is doing.
May also be multiple diagnosis. Like the other fellow said, possibly bad board. But the compressor overamping would be a problem in the outdoor unit. I've seen em appear clean, to all observation. But apply some coil cleaner, and the amps came down.
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Thanks for the response.
Since the unit's several years old and has never been recharged, I would hope the freon pressure hasn't changed. Of course, the condenser could be dirtier than it appears and I'll certainly give it a good cleaning.
Thanks again - Ken
Stormin Mormon wrote:

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That's a recipe for low on freon. Several years old, and not been serviced.
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