DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (http://www.diychatroom.com/)
-   HVAC (http://www.diychatroom.com/f17/)
-   -   Heat pump starts initially but will not come back on to maintain temps (http://www.diychatroom.com/f17/heat-pump-starts-initially-but-will-not-come-back-maintain-temps-119266/)

johnniebravo 10-05-2011 07:22 AM

Heat pump starts initially but will not come back on to maintain temps
 
First post here and looking for some assistance with troubleshooting my heat pump. I have been living in my house for 2 years, I believe the system is original to the house and was installed in 1998. When I first moved into the house the heat pump worked fine, the system would heat and cool fine. In heat mode, if the temp dropped too much the aux heat would kick in. The system is a carrier weathermaker 8000TS heat pump system with a natural gas aux/emergency heat backup, the outdoor unit is a comfortmaker. The air conditioner works fine, no problems except with it freezing up twice this summer because 1) the indoor blower motor died and 2) after i replaced motor I had too many vents blocked off preventing sufficient airflow over the coil to prevent freezing. To elaborate on the previous cooling problem, I replaced the inside blower motor and capacitor as well as the outside compressor/fan capacitor. No more freeze ups once i corrected the mechanical failure and dumb move of blocking vents to boost airflow to upper floors. Lesson learned.

The AC part of the system works fine, if i turn it on via the thermidistat (TSTATCCPRH01-B), the indoor blower starts as well as the outdoor compressor and fan. House cools fine.

Now on to my current problem that first appeared last winter. With the heat pump system switched to off (for an extended period) and then switching it to heat, the thermostat (set at 72, with an indicated indoor temp at 70 or less) will show the heat indicator on the lower right. The indoor blower will turn on and the outdoor compressor and fan will kick on. The low and high pressure lines will quickly warm and the system will heat very well. House heats up quick, Yay! Well, after the target temp is reached the system will turn off as it should. This is where the problem happens, after a few hours the house temp will slowly fall and the thermostat will kick on and show the heat indicator again in the lower right and the indoor fan will turn on BUT the outdoor compressor and fan will not turn on. The thermostat will continue to run the indoor fan and show the heat indicator but the outdoor compressor and fan will not turn on again. Usually this happens after i go to bed in the evening and the fan will run all night with the temperature slowly dropping all night. I usually wake up to a cold house and then switch the system manually to Emergency heat. The emergency heat works wonderfully! The house gets warm in a matter of minutes. Thing is the system used to switch to e-heat automatically, it doesn't do it anymore (another symptom?). Over the past few days the temps were in the 40s, which are plenty high for the heat pump to work efficiently (I live in the Washington DC area).

So my question is what would cause the heat pump to heat perfectly fine for the first cycle of heat when turned on from an off position but not allow the outdoor unit to come on when its re-called after temp drops? Second is why does the system no longer switch to aux/e-heat on its own?

Just this morning i noticed something strange, the system was running as it normally does when i wake up....fan running with the heat indicated on the thermostat but outdoor unit not running and house temp dropping. Well, today is supposed to be 75degrees so i just turned it off for the day. WEll before turning it off the system showed house temp as 70 deg with a target of 72...it was attempting to get there. Approx 2-5 minutes after shutting the system completely off, i walked by the thermostat again and it said the internal temp was now 72 degrees. Is this a sign of a defective thermostat? it said it was 2 degrees cooler with the system running just ~3 minutes ago???

Additional details, again, i just replaced the indoor blower motor due to a failed front bearing, replaced capacitor. Indoor coil looks OK too. Outside, i hosed off and vacuumed the compressor unit, and changed out a weak capacitor. The contactor is aging but works perfectly fine, visually inspected it as it turned on and off. Air filter is clean and is replaced regularly. The contactor is getting 240v and the defrost board is also getting 24v.

My obvious observation is when the system is running in heat mode, not on the first start-up, the contactor is not getting a signal to activate the outside system. What could cause this condition? what would cause aux heat to no longer automatically switch on? Am I looking at a bad defrost board outside? With the indoor furnace working fine as well as all the fan controls I am inclined to say that part is working fine and the only electronics or parts are on the outside unit. I am convinced that the problems lies outside. To my knowledge, the outdoor unit has never frozen over. Last thing, the LED on the indoor board has not indicated any faults, its a solid red LED all the time.

Any help is appreciated. I've searched a bit but didn't find any answers. If I've missed a previous thread, please point me in that direction and will try what is recommended there.

Done That 10-05-2011 01:27 PM

So maybe start checking the Tstat outputs for 24V signals. For example, is there a Y1 compressor call at the outdoor unit when the thermostat has it's pump heat icon active? The defrost board only calls for back-up heat during a defrost...normal back-up/emergency heat is called for by the W1 output of the thermostat, or the E emergency terminal (sometimes these are jumpered together anyway).

Sometimes outdoor units that run and then stop are tripping on their internal protector..due to issues like low refrigerant charge. When the protector resets the units can run again. In summer it can take hours for a reset...but you had no summer cooling issues so this doesn't appear to be your issue.

I lean to someting inside / Tstat / wiring.

johnniebravo 10-05-2011 02:37 PM

I am leaning towards something inside too especially since the thermostat no longer automatically switches over to aux/e-heat on its own anymore. Is there a chance I have a low charge that is sufficient for summer cooling but not good enough for effective heat during cold months?

By compressor call? Do you mean does the unit outside get a 24V signal at the circuit board? I am also going to assume Y1 = the Yellow labeled terminal.

The defrost board also seems to serve as the brain for the outdoor unit. Is this a correct assumption?

A few additional details, the heat pump model # is: CHP242AKA1

The board in the outside unit is: ICP Products Defrost Control Board 1069364

Doc Holliday 10-05-2011 02:40 PM

I'd start off with the stat as well as in replacing it. You did say you had no cooling issues which would lead me to believe all is well although if you had a lineset problem such as a stuffed drier then that could lead to pressure switch problems which would cut off the outside unit.

We'd need to know if you have low voltage to the outside unit on each call (cycle) for heat.

johnniebravo 10-05-2011 02:46 PM

Would low line voltage show up when the unit is operating fine on the first startup? Or would it only show when the unit is not coming on to maintain heat?

I tested line voltages at the outdoor board yesterday and found the following:

compressor and fan OFF measuring Volts AC
R C O Y W
27v .010 .017 .049 .002

Done That 10-05-2011 02:57 PM

The control board is always fed 24V from the indoor transformer.

The thermostat turns on a relay to send 24V to the Y terminal on that defrost board when there is a cooling or heating demand that requires the compressor to run. So you should be able to measure 24V demand signal when your thermostat is outputting a heat/cool demand...on Y at the board. The control may have a 3 or 5 minute short cycle delay timer, and then it should energize the contactor from the CC terminals (if I have that board right in my head).

Be carefull because the fan relay on that defrost control is breaking line voltage...so that board can bite you if you are not paying attention.

In this case I'm with Doc...I would put on a new Tstat and see if that takes care of it...worst case you have a nice new Tstat.

Otherwise bring in a pro and he'll have you straightened out in no time.

johnniebravo 10-05-2011 03:09 PM

Just turned the heat on inside and quickly ran outside, the Y terminal registered 26.72 volts and the unit came on. It ran for approx 3 minutes then shut off. Temp inside had climbed in that short period by 2 degrees....which i thought was fast. Similar to this morning when I shut it off and it then jumped 2 degrees.

anyway, after the outside compressor shut off, the heat icon was still on at the thermostat and the line remained at 26.72V.

The voltage fluctuates from 25 ish to 26 ish.

Master of Cold 10-05-2011 06:08 PM

Look inside the compressor area. You will have 2 red or pink (the colors fade) that are probably laying on the hot gas line. Examine these wires and see if they have been damaged.

Marty S. 10-05-2011 06:30 PM

Quote:

Originally Posted by johnniebravo (Post 742799)
Just turned the heat on inside and quickly ran outside, the Y terminal registered 26.72 volts and the unit came on. It ran for approx 3 minutes then shut off. Temp inside had climbed in that short period by 2 degrees....which i thought was fast. Similar to this morning when I shut it off and it then jumped 2 degrees.

anyway, after the outside compressor shut off, the heat icon was still on at the thermostat and the line remained at 26.72V.

The voltage fluctuates from 25 ish to 26 ish.

Since you still had 24 volts at Y outside and the compressor was not running then that narrows it down to the heat pump. There's the defrost board, a high pressure switch and maybe a discharge sensor. Narrow it down by checking to see if the sensors are open or closed when the system faults. If they check out fine then it's the defrost board. If the sensors are open then there's likely still an air flow issue inside and the sensors are doing their job protecting the compressor.

johnniebravo 10-05-2011 06:44 PM

Quote:

Originally Posted by Master of Cold (Post 742897)
Look inside the compressor area. You will have 2 red or pink (the colors fade) that are probably laying on the hot gas line. Examine these wires and see if they have been damaged.

I looked in the compressor area and did not notice red lines, there are yellow lines wrapped around the smaller copper tube (high pressure line??). It's dark out now so I will have to hold out until tomorrow afternoon.

johnniebravo 10-05-2011 06:54 PM

Quote:

Originally Posted by Marty S. (Post 742916)
Since you still had 24 volts at Y outside and the compressor was not running then that narrows it down to the heat pump. There's the defrost board, a high pressure switch and maybe a discharge sensor. Narrow it down by checking to see if the sensors are open or closed when the system faults. If they check out fine then it's the defrost board. If the sensors are open then there's likely still an air flow issue inside and the sensors are doing their job protecting the compressor.

I would like to check the voltage to the board after the thermostat has called for heat for an extended period and the temp is falling...like when I wake up in the morning. Problem is the temps are back up to 75ish degrees now. So, not sure if I will have the opportunity any time soon.

Regarding the sensors being open or closed, I have no idea of how to do that. I assume with my multimeter?

And with the air flow, all vents are open with the exception of the sole vent in the basement. It is very high pressure considering how close it is to the indoor unit.

Should I hold off on a thermostat until i can test the rest?

jfrotten 10-05-2011 06:59 PM

It sounds like a tstat to me... the tricky part in diagnosing is hopeing that the original installer wired with the traditional colors (probably). Take the tstat completely off of the wall and go get a wire nut. Nut the red, yellow and green wires together. This is the heat pump in heat mode and the air handler. If your unit runs and heats normally, add the white wire. This should be your secondary heat, gas or electric. The heat pump should continue to run but your secondary should kick on. Connecting these wires at different times is all your thermostat really does... if you can do it manually and everything works, then your thermostat is either not wired/set up correctly or it's bad.

johnniebravo 10-05-2011 07:09 PM

Quote:

Originally Posted by jfrotten (Post 742939)
It sounds like a tstat to me... the tricky part in diagnosing is hopeing that the original installer wired with the traditional colors (probably). Take the tstat completely off of the wall and go get a wire nut. Nut the red, yellow and green wires together. This is the heat pump in heat mode and the air handler. If your unit runs and heats normally, add the white wire. This should be your secondary heat, gas or electric. The heat pump should continue to run but your secondary should kick on. Connecting these wires at different times is all your thermostat really does... if you can do it manually and everything works, then your thermostat is either not wired/set up correctly or it's bad.

Jfrotten,

Thanks for the reply. The thing to consider here is that if i turn the system on after it has been off, it will heat the house up to the desired temp very quickly. After a few hours when it needs to come back on, it won't, but the indoor blower fan does come on along with the heat icon the tstat. Could I be dealing with an intermittently functional tstat? It seems to me that the only way to tell is to wait till it acts up and then see if the voltage is present at Y.

jfrotten 10-05-2011 07:25 PM

It's definitely the thermostat. The question is, is it intermittenly defective (unlikely) or set up incorrectly. Either way, if you do your test and find no voltage at y, the it could only be the thermostat. If you do your test and find voltage at y, then there is an intermitten fault in the outside unit. I think that your installer set up on your thermostat is set to use your heat pump as your aux instead of your primary. It's either set that way or wired that way. It's almost easier to replace the thermostat then it is to explain how to ensure it is set up and wired correctly. I think that everything is functioning the way that it is set to function. Can you post a picture of the wires hooked into your thermostat back plate? One that shows both the wire colors and the letter labels of the terminals...

jfrotten 10-05-2011 07:35 PM

Quote:

Originally Posted by johnniebravo

anyway, after the outside compressor shut off, the heat icon was still on at the thermostat and the line remained at 26.72V.

The voltage fluctuates from 25 ish to 26 ish.

where did you measure this voltage? The red wire?


All times are GMT -5. The time now is 11:57 PM.


Copyright 2003-2014 Escalate Media LP. All Rights Reserved