Outdoor Heat Pump Runs after inside unit turns off

Problems related to residential installations.

Outdoor Heat Pump Runs after inside unit turns off

Postby jdc126 » Sat Aug 18, 2012 8:58 pm

Hi All,

Heat Pump -
Outdoor Rudd ~13 yrs
Indoor Rheem ~2 yrs

I noticed a few weeks ago that my indoor coils were icing up/frosting over. I called a tech who noticed that I had too many vents closed and also cleaned my outdoor coils. I also replaced with a new filter. My house both before and after would cool very well except when frosted. I also informed the tech that it seemed like there was still liquid flowing when the inside unit was off. He responded that this may just be normal cycling. This only seemed to happen when the indoor coils were frosted. Tech also checked all contacts and temps and said the unit is in perfect working order. Fast forward a week and no real change. Tech returned with no idea of the problem and decided to try increasing the speed of the indoor blower. This worked fine for a few days. Fast forward a week and then I noticed that the outdoor unit would not turn off and the only way I could get it off was to use the breaker. Tech came and fixed the contactor which was burnt. Unfortunately this still didn't fix the original problem but got it working again. As this story continues I've been paying more attention and I have noticed that there are times when the thermostat will click on and both the indoor and outdoor unit turn on and blow nice cold air. The indoor unit will turn off/stop blowing when the temperature is reached but the outside unit continues to run and will eventually turn off. I timed it once and it was about 45 minutes. The outdoor unit will turn off if I use the thermostat. The two units sometimes work in sync and sometimes the outdoor unit stays on. This then leads to the indoor coils frosting up.

I've searched online with no ideas and am reluctant to call the same company back but would hate to call another person if this is truly not a hard problem to solve. Welcome any thoughts or ideas. I'm handy and can use a voltmeter if needed. Other info that may or may not be of interest I purchased and installed a new programmable thermostat about a year ago.

Thanks!
jdc126
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- Outdoor Heat Pump Runs after inside unit turns off

Postby Freon » Sun Aug 19, 2012 2:33 pm

The next time the thermostat is satisfied and the indoor air handler stops but the outdoor condenser continues (sometimes up to 45 minutes you said) go to the air handler control board and find the Y and C terminals. Measure the AC voltage between them. With the thermostat satisfied as to temperature there should be zero volts between the Y (goes out to the condenser contactor) and the C terminals at the air handler.

If you measure 25 volts between Y and C at the air handler then your thermostat is still sending a call for cooling to the condenser after the thermostat has stopped the air handler blower. I would think your thermostat is bad/flaky.

If you measure zero volts between Y and C and the outdoor condenser is still running then you need to measure the 25 volt AC voltage at the contactor at the condenser. To do this first pull the 240 volt breaker to the condenser. Then access the electrical compartment on the condenser and measure the voltage at the contactor coil (thin wires). If you have 25 volts then you have a short somewhere in the control wiring or the condenser control board is flaky. If there isn't 24 volts Ac then the contactor may be welding closed due to a very high current draw by the compressor. You'll need a tech with an ammeter to measure the compressor current draw and compare it to the RLA amps as stated in the data plate on the condenser.
Freon
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- Outdoor Heat Pump Runs after inside unit turns off

Postby jdc126 » Sun Aug 19, 2012 4:49 pm

Freon,

Thanks, this sounds like the most logical rational thing I have heard so far. I will give it a try and see what is going on and get back. Thanks again!
jdc126
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- Outdoor Heat Pump Runs after inside unit turns off

Postby Trini2dbone » Thu Sep 06, 2012 3:06 am

jdc126 -
> Hi All,
>
> Heat Pump -
> Outdoor Rudd ~13 yrs
> Indoor Rheem ~2 yrs
>
> I noticed a few weeks ago that my indoor coils were icing up/frosting over.
> I called a tech who noticed that I had too many vents closed and also
> cleaned my outdoor coils. I also replaced with a new filter. My house
> both before and after would cool very well except when frosted. I also
> informed the tech that it seemed like there was still liquid flowing when
> the inside unit was off. He responded that this may just be normal
> cycling. This only seemed to happen when the indoor coils were frosted.
> Tech also checked all contacts and temps and said the unit is in perfect
> working order. Fast forward a week and no real change. Tech returned
> with no idea of the problem and decided to try increasing the speed of the
> indoor blower. This worked fine for a few days. Fast forward a week and
> then I noticed that the outdoor unit would not turn off and the only way I
> could get it off was to use the breaker. Tech came and fixed the contactor
> which was burnt. Unfortunately this still didn't fix the original problem
> but got it working again. As this story continues I've been paying more
> attention and I have noticed that there are times when the thermostat will
> click on and both the indoor and outdoor unit turn on and blow nice cold
> air. The indoor unit will turn off/stop blowing when the temperature is
> reached but the outside unit continues to run and will eventually turn off.
> I timed it once and it was about 45 minutes. The outdoor unit will turn
> off if I use the thermostat. The two units sometimes work in sync and
> sometimes the outdoor unit stays on. This then leads to the indoor coils
> frosting up.
>
> I've searched online with no ideas and am reluctant to call the same
> company back but would hate to call another person if this is truly not a
> hard problem to solve. Welcome any thoughts or ideas. I'm handy and can
> use a voltmeter if needed. Other info that may or may not be of interest I
> purchased and installed a new programmable thermostat about a year ago.
>
> Thanks!

You say this is a heat pump system. Can you provide model nos. for the outdoor unit?
Heat pump systems require a speciall thermostat as it has a special terminal for a reversing valve. Did you purchase a heat pump stat and are you sure you wired it correctly?
Trini2dbone
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- Outdoor Heat Pump Runs after inside unit turns off

Postby jdc126 » Thu Sep 06, 2012 8:09 pm

After all this time things have been working without any issues. Today I came home and found that this was happening so I was finally able to measure the voltage. With the indoor unit off and the outdoor unit on there was 25v going to both units.

Rudd upka-030jaz
Carrier fb4cnf030
Thermostat Honeywell rth7400/rth7500 series

Not sure if I can post a picture but I'll do so of the thermostat wiring.

Thanks!
jdc126
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- Outdoor Heat Pump Runs after inside unit turns off

Postby Trini2dbone » Fri Sep 07, 2012 4:05 am

jdc126 -
> After all this time things have been working without any issues. Today I
> came home and found that this was happening so I was finally able to
> measure the voltage. With the indoor unit off and the outdoor unit on there
> was 25v going to both units.
>
> Rudd upka-030jaz
> Carrier fb4cnf030
> Thermostat Honeywell rth7400/rth7500 series
>
> Not sure if I can post a picture but I'll do so of the thermostat wiring.
>
> Thanks!
During this scenario, is the stat satisfied or is it still calling for cooling?
Trini2dbone
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- Outdoor Heat Pump Runs after inside unit turns off

Postby jdc126 » Sat Sep 08, 2012 10:17 am

@Trini2dbone The thermostat, at least when I saw it, was not satisfied. It was warm inside because the coils were frosted over so not cooling the house but still running. However, in the past when this issue was happening I have heard the thermostat click off but the outdoor unit continued to run.
jdc126
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- Outdoor Heat Pump Runs after inside unit turns off

Postby Trini2dbone » Sat Sep 08, 2012 2:48 pm

jdc126 -
> @Trini2dbone The thermostat, at least when I saw it, was not satisfied. It
> was warm inside because the coils were frosted over so not cooling the
> house but still running. However, in the past when this issue was happening
> I have heard the thermostat click off but the outdoor unit continued to
> run.

In your previous post you indicated the indoor unit was off but the outdoor unit on and there was 25v at the outdoor unit contactor.
If the stat was not satidfied and calling for cooling then the indoor unit fan should have been on. No or low air flow across the evaporator coil is one of the causes for the coil to freeze up. The problem could be the indoor unit fan control or the new stat.
Open the indoor unit lower panel to find the control circuit board, if there is a door switch you will need to keep this depressed in order to trouble shoot. Becareful as some terminals and connection maybe "LIVE". Locate on the board the stat conections. usually designated with the letters G Y C W O RC RW. With your voltmeter set to VAC and with the stat calling for cooling there should be 24vac across c & y and c & G.
While your at these terminals it won't hurt to verify the wiring connection between the stat and indoor unit. Verify the wiring colours match the terminals at both ends.
When you replaced the stat did you follow the 'Installers Set-up'? With Honeywell stats there is a code for the stat to control the indoor fan in cooling mode or to have the indoor unit control the fan. Usually the stat controls the fan in cooling mode; verify this as well.

Good luck.
Trini2dbone
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