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#1
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HVAC question...
Guys, I have a fairly new system for the upstairs - heat pump, R410/puron, scroll compressor. When it was installed, it was supposed to a fairly high end unit.
Well now, about 6 years later, it won't start. When the compressor tries to run, it just buzzes for about 5 seconds then clicks and quits. Then, about 10 seconds later, it does it again and keeps repeating but never gets started. I can probably figure it out eventually, either the starter capacitor or contactor but if anyone knows for sure, it would sure save me a lot of time. Thanks for any help you can give!
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 Last edited by KarTek; 01-30-2011 at 07:13 PM. |
#2
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I've seen this problem with some AC units.
There are a few pressure switches ... usually one on each side of the compressor. One's a High and the other's a Low Pressure switch. With the system off, the pressure on both sides of the compressor will "even out" - since it's a closed-loop system, the pressure will equalize the longer the system is idle or not pumping. But, when the pump starts, there's usually a "delay" switch that will prevent the compressor from shutting off for a preset time until the system has a chance to build up the right pressures on both sides of the compressor...lower pressure on the supply-side to the compressor and high-pressure on the exit side of the compressor. If the "delay shut-off" relay drops out and either one of the the pressure switches is in an "off" state or "THERE'S SOMETHING WRONG HERE!" state, then the compressor shuts off for a predetermined time, then it will either try again or in a more expensive situation, trip out and then send an alarm to a monitoring point or station. Since it's been 6 years since you've had it installed, the question, first, would be: When was the last, if ever, time you had the unit serviced? If never, now's the time to call in the calvary. The best time for doing any of this work is usually during the begining of the cooling season for ACs...the service techs like to see the ambient air temperature around 75° to 80° and a relative humidity level of something just about the top end of "comfortable" - whatever that is... As for a HP? That's their call. They probably have a "balance point" for ambient air and humidity that's an all-around good testing/setting-up point that works both sides of the seasonal setup for their gear. GL and let us know what happens! BTW: I've seen AC Techs use a standard tire guage just to check to see if the system has ANY gas in it. CAUTION; NEVER WHILE THE SYSTEM WAS ON/RUNNING. ONLY WHEN IT WAS OFF AND THE SYSTEM HAD A CHANCE TO "BALANCE OUT" - through years of experience, some of the techs were able to tell if a particular system had enough "juice" or not by just what the stick told them...and usually, after cleaning the fins and compressor out, they'd be within 40-60psi on the high-side and about 0-5psi on the low-side. Experience shows!!!
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. . M. G. Burg'10 - Dakota SXT - Daily Ride / ≈ 172.5K .'76 - 450SLC - 107.024.12 / < .89.20 K ..'77 - 280E - 123.033.12 / > 128.20 K ...'67 - El Camino - 283ci / > 207.00 K ....'75 - Yamaha - 650XS / < 21.00 K .....'87 - G20 Sportvan / > 206.00 K ......'85 - 4WINNS 160 I.O. / 140hp .......'74 - Honda CT70 / Real 125 . “I didn’t really say everything I said.” . . . . . . . . . . . . . . . . . . ~ Yogi Berra ~ |
#3
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First:If the fan does not turn then that is the problem.
Second: Remove the side panel and see if the capacitor is swollen,if so replace it. Also check the contactor to see if the contacts are burnt. |
#4
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The unit is definately stalled out. I hear a big buzz every time it tries to start.
So, is the capacitor under a side cover or is it on the compressor? Thanks for the insight so far. I'll probably get back on it this weekend.
__________________
-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#5
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A residential HVAC system with high or low pressure safety switches would be a surprise. A failed run start capacitor would be the first thing to check. If the capacitor is OK. Check the compressor. Remove the cover where the wires are connected to the compressor. Trace the wires to where they are connected to the power relay and capacitor. Carefully observe and mark where they were removed. These will be the run start and common connections. None of these should read to ground. Do not try to remove the wires from the compressor. I only mention this so as not to damage the fusetite terminal assembly. (there is system pressure behind the terminals) Hopefully it is a defective capacitor. The only other device that comes to mind may be a compressor dead headed against a stuck reversing valve. (thats a reach) Allowing the compressor to continually try to start is not a good thing. There is an internal overload inside the compressor. When it cools down and closes the circuit the compressor will try to start. Last but not least check the supply voltage it should be 220v. Good Luck
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#6
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I dug into it today since it was nice outside and here's what I found:
It actually DOES have high and low pressure switches, just like an automotive type system. However, I don't think that's the problem in this case. I pulled the capacitor (it was very to locate and identify) and it was slightly swollen, leaking a clear oil from around the terminals. I'm ordering a new one and we'll see how that does.
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-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#7
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#8
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Cool, thanks.
__________________
-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#9
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#10
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Not really "every year", more like I blow it off every time I'm doing yard work or using the leaf blower. It's pretty clean.
__________________
-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#11
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Check the resistance of the start/run windings.
A common compressor failure is the rotor in the compressor locking up (locked rotor condition), which would cause a hum for 5-10 seconds before the motor windings overheat and are shut down by the internal thermal protector in the compressor. Check the resistance of the run/start windings after the humming stops to determine if it shows an "open" winding which would have been caused by the thermal protector opening the circuit. Heat Pump compressors generally last 10-12 years (average).
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#12
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OK, just to wrap this up. I picked up a new capacitor at ACR on Friday and installed it yesterday. The old one had swollen and the top where the terminals was somewhat dome shaped with a clear, oily liquid oozing from inside.
$7 part and it works like a charm now! Thanks for the suggestions!
__________________
-Evan Benz Fleet: 1968 UNIMOG 404.114 1998 E300 2008 E63 Non-Benz Fleet: 1992 Aerostar 1993 MR2 2000 F250 |
#13
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