Heatpump - sometimes it works and sometimes not

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Old 02-09-12, 02:46 PM
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Heatpump - sometimes it works and sometimes not

I have a Concept 1000 by Armstrong Air model # SHP10G30A. A few months ago I started having cold air coming out of the vents all the time. I only had warm air when the green "aux heat" light is on. So I had to constantly walk over to the Honeywell T874G Thermostat and turn up the heat until the green light comes on, and then remember to walk over and turn it back down so it will stop blowing cold air after the green light goes off. I figured it was just a bad cap in the heatpump and would get around to checking it eventually. In the mean time I walked out to check the mail and thought "Is that the heatpump running?" Sure enough, it was. Warm air was coming out and the green light was off. Hmmm... maybe it fixed itself. Nope. Wasn't long till cold air was coming out again. So I checked the cap, of course it checked out fine. Not knowing what to do next I called a friend that's in the HVAC business. He came and checked everything and said I needed a new Defrost Control Board and Defrost Sensor. So I ordered and installed new ones. Seems like it worked right for about a week and now its back to the same ole thing.... blowing cold air and heatpump only works some of the time. My friend has no clue what it could be. Does anyone here have any idea what could be causing this?
 
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Old 02-09-12, 03:12 PM
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while it is blowing cold air is the outdoor fan running ( or is it in defrost)? While it is blowing cold air is the large copper line leaving the outdoor unit hot/warm? Do you have electric or gas backup heat?
 
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Old 02-09-12, 04:13 PM
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No the fan is off, the line is cold. I have electric backup.
 
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Old 02-09-12, 04:33 PM
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While it is blowing cold does the outdoor unit run at all? If no. How did you check the capacitor? Does your HP have a hard start? While it is blowing cold is the contactor pulled in?
 
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Old 02-09-12, 05:22 PM
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Sometimes the outdoor unit runs, most times not. When its blowing cold, the outdoor unit does nothing. The contactor is not pulled in. I can push it in with a screwdriver and it runs until I let go with the screwdriver. It does not have a hard start cap. The unit is roughly 5yrs old. I have a cap checker on my DVM. Its within spec. Also, the compressor starts right up with no problem, so the cap is obviously working.... So does the fan.

To me its like the unit receives a signal to kick on sometimes. And sometimes not. At this moment its blowing cold air around. The next time I reply it may be working. Its a crap shoot.
 
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Old 02-09-12, 05:26 PM
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I take it that this is something new, so there is no outdoor thermostat involved or anything... SO, I would check for voltage from Y to C in the air handler while the unit is blowing cold.
 
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Old 02-09-12, 05:39 PM
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I think my friend did that. Or at least he checked the voltages on the wires on the thermostat. But if the voltage from Y to C is out of spec, what does that indicate?
 
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Old 02-09-12, 05:43 PM
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Also, there is a defrost thermostat outside.. .which I replaced along with the control board. I don't know if there is another thermostat outside or not. All I know is there are a MILLION wires going into that control board!
 
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Old 02-09-12, 06:30 PM
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if the unit is blowing cold and Y to C does not show voltage it would indicate a faulty stat.
 
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Old 02-09-12, 06:58 PM
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I see Y, but where is C?

 
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Old 02-09-12, 07:14 PM
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you are showing the thermostat. You need a schematic of the air handler.
 
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Old 02-09-12, 07:20 PM
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I can't get to the air handler without tearing a wall down. Wouldn't all the wires meet at the thermostat? I wouldn't think the problem is in the air handler.
 
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Old 02-09-12, 07:36 PM
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Can I just measure voltage across Y and C on the defrost control board on the outside unit?
 
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Old 02-09-12, 08:24 PM
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Yes. But we reply need to measure out from the stat to find where the signal is dropping. Stat, Ahu, hp? Won't know till some measurements are taken.
 
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Old 02-09-12, 09:30 PM
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Well, I would have to tear out a wall to get to the air handler. If Y is the wire that closes the contact and C is the common, it makes sense to measure at the heatpump to see if signal is getting that far. So tomorrow during daylight I'll measure across those and report back. I'm pretty sure my friend already measured that because I asked if the signal was reaching the outside unit from the stat... Thinking maybe an animal chewed one of the wires under the house. He said all that was good and it had to be the control board. (He's been in the HVAC business for a long time and I'm pretty sure he covered the basics. He even checked the pressure). Anyway, If signal is reaching the heatpump, yet the compressor isn't coming on, then what?
 
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Old 02-10-12, 03:25 AM
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You should not have to tear out a wall to get to the air handler. That is against code. What happens when your blower motor fails? You are required to have access to the AHU.

IF the correct signal is applied to the defrost control and it does not operate we need to make sure that you are not in a 5 min compressor delay. This can often be verified by a LED on the defrost control. Certain flashes give you diagnostics.

Your friend "has no clue what it could be", so we need to cover all the basics for proper diagnostics no matter what he has done or not done. Things get overlooked.
 
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Old 02-10-12, 09:54 AM
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Ok, I have 26.5 - 27.5 volts and the heatpump is not running. I can watch the DVM from the window and it varies by roughly 1 volt (seems to drop a volt when the em heat comes on). I'm curious how many volts it reads when the pump kicks on.

I guess my house is not up to code because there is no way to access the air handler without removing a wall. I have a bathroom on 1 side, living room on another, bedroom on another, and a closet on the other. The easiest would be to remove the closet wall.
 
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Old 02-10-12, 09:57 AM
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Oh, and there is no 5 min delay because the air handler runs longer than 5 mins, yet the heatpump never comes on. If its going to come on, it will come on instantly.
 
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Old 02-10-12, 10:11 AM
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Where are you taking this reading. Before the defrost control or after at the contractor. Your HP should have safeties that may wire in series with the contactor circuit.
 
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Old 02-10-12, 10:16 AM
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I just took the wire nuts off the yellow and blue wires and clipped the DVM to them. The yellow goes into the Y on the board and the blue into the C on the board. I also measured the CNT, which is another yellow wire going from the board to the contactor. Got zero volts there. So, signal is going into the board, but nothing is coming out.

Here's a dumb question. What would happen if I just hook the Y yellow wire to the contactor instead of the board? I'm just curious.
 
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Old 02-10-12, 11:00 AM
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Here is the board. If there are any safeties, they are integrated in the board. The wire coming from CNT goes straight to the contactor.

 
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Old 02-10-12, 01:18 PM
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Ps1 and ps2 are pressure switch terminals that will keep the HP from running.
 
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Old 02-10-12, 01:26 PM
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Unplug them and see what happens?
 
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Old 02-10-12, 01:32 PM
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I don't know what unplugging them will do without a schematic. They are safety switches to protect your compressor from damage. Best to leave them hooked up and see if they open the circuit. Again. I need a schematic to tell what readings should or should not be. Also need to see what us going with the refrigerant which will need to be done by a certified tech.
 
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Old 02-10-12, 01:36 PM
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He checked the pressure when he checked everything else. He seemed pretty impressed with the pressure. I just checked the voltages... PS1 is the same voltage as Y. PS2 is nothing. I'm wondering what would happen if I jumper Y to PS2. Maybe both need to see voltage or the board assumes there is a pressure problem.

Or maybe I could run it in AC mode and see what the voltages are on PS1 and PS2.
 
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Old 02-10-12, 01:48 PM
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Is ps2 on high or low side of system. Even if the pressures were OK when he was there does not mean they are OK now. You now know what is keeping the system from running. Have that part of the system checked. This will tell you if it is a fault switch or a refrigerant issue.
 
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Old 02-10-12, 02:04 PM
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Yes I think you hit on something. It doesn't work in AC mode either. I'm going to cut the power and look inside to see if I can determine if its a high or low side switch. How can I tell which is high and which is low?
 
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Old 02-10-12, 02:07 PM
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Post a pic. That would be the best way. Include as much as possible in the oic of surrounding refrigerant lines.
 
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Old 02-10-12, 02:29 PM
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Well, PS1 and PS2 are the same switch. And I found a wire diagram on the case I'm trying to scan it and post. According to the diagram, its the low pressure switch and it says its optional. So I disconnected it. Compressor still won't come on, but I found the voltage at PS1 still same as Y and PS2 is dead. So I'm thinking a jumper from PS1 to PS2 would make it work. I measured the resistance across the pressure switch and it started at 80k ohms and gradually increased to 130k ohms and I got tired of watching it go up forever. Such large resistance would explain why no voltage is making it back to PS2.
 
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Old 02-10-12, 02:39 PM
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So the switch is open. Have the pressure rechecked before condemning the switch. I would not bypass the switch as it is to protect your compressor from a low pressure condition. This condition may be due to a restriction, faulty piston or TXV, or low charge.
 
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Old 02-10-12, 02:52 PM
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It says optional. I just want to see if it will work if I jumper it. Once I verify it does, then at least I know there is either a problem with the pressure or the switch.





 
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Old 02-10-12, 03:12 PM
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The jumper fixed it. Heatpump is running and have heat coming out now. The DVM shows 19.5 volts on the Y to C when running. Was 26.5 before. Is that normal?
 
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Old 02-10-12, 08:09 PM
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It should still be around 24V. That is a bit low. The contactor may need replaced to resolve the low voltage.

DO NOT RUN THE HP WITH THE JUMPER IN PLACE. Have it checked first.
 
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Old 02-10-12, 10:54 PM
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Is it the contactor or the transformer supplying the voltage? The points do look like they need to be filed or something.

I talked to a guy that does the HVAC work for the carpet mills around here. He said its probably not a piston or TXV because I would hear something out of the ordinary like a screech. He said its not a stuck half-open reverse valve or it wouldn't heat as well as it does. If I had a restriction I would have super high high-side pressure and very low low-side pressure, it just doesn't seem very likely because we had gauges on it before and the low side was fairly high. Plus the thing runs like its new. Nice n smooth. He said if its low on refrigerant, the worst that will happen is the whole unit will turn to a block of ice. So I put my hand on the cooling fins and they're about as cool as a can of beer from the fridge. He also said many units don't have low pressure switches. And my wire diagram seems to back that up saying "If Used", leading me to believe its not all that important to have one. I read a manual for a Lennox control board and it states the board comes with a jumper installed from the factory (which is where I got the idea to do mine). Does all this sound reasonable?

I sure appreciate your assistance! It sure is nice to have heat instead of the AH blowing cold air around for hours at a time.... And just in time for a cold snap! Supposed to be down to 20 degrees tomorrow night. Good weather to see if the HP ices up
 
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Old 02-11-12, 05:32 AM
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I talked to a guy that does the HVAC work for the carpet mills around here. He said its probably not a piston or TXV because I would hear something out of the ordinary like a screech. He said its not a stuck half-open reverse valve or it wouldn't heat as well as it does. If I had a restriction I would have super high high-side pressure and very low low-side pressure, it just doesn't seem very likely because we had gauges on it before and the low side was fairly high. Plus the thing runs like its new. Nice n smooth. He said if its low on refrigerant, the worst that will happen is the whole unit will turn to a block of ice. So I put my hand on the cooling fins and they're about as cool as a can of beer from the fridge. He also said many units don't have low pressure switches. And my wire diagram seems to back that up saying "If Used", leading me to believe its not all that important to have one. I read a manual for a Lennox control board and it states the board comes with a jumper installed from the factory (which is where I got the idea to do mine). Does all this sound reasonable?

I'm glad it is working for you. You seem to have everything figured out. I hope the system is not low on charge or does not have something else causing what is happening. Good luck with whatever you decide to do with the system.
 
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