Honeywell RTH7600D - Second Stage Electric Heat

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Old 01-11-13, 11:58 AM
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Honeywell RTH7600D - Second Stage Electric Heat

[h=2]Hi,[/h]

I have a Honeywell
RTH7600D T-stat and a Carrier heat pump with electric emergency heat. I don't like the extra cost of the emergency heat and would like to disconnect it if I can without causing any problems. The emergency heat is rarely used but cost a lot when it comes on. I would like to go without and just put up with the brief drop in temp. There is a wire on E and Aux. I am wondering if I can just pull one or both of the wires to disable it. Can Anyone help with this?

Maybe I should have said that I would like to stop the second stage from coming on? Can I change the second stage set point?
 
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Old 01-11-13, 04:16 PM
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You can unwire Aux to drop out stage 2 heat.
E is for emergency heat. I would leave it wired.
 
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Old 01-11-13, 05:20 PM
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Thanks.

My programming is currently:

170 7
190 0
270 9
300 1


Can I just change program code 170 from 7 to 2 to disable the second stage without removing the Aux wire (just in case I change my mind)?

How should I set code 190? It is set to 0. I have a orange wire hooked up labeled O. How can I double check that I have this setting correct?
 
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Old 01-11-13, 06:13 PM
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Can I just change program code 170 from 7 to 2 to disable the second stage without removing the Aux wire (just in case I change my mind)?
You'd lose emergency heat.


How should I set code 190? It is set to 0.
Carrier outdoor units would need 190 set to 0 (energize the reversing valve for cooling).


How can I double check that I have this setting correct?
If 190 is set incorrectly, you will get heat when you give the stat a cooling demand.
 
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Old 01-11-13, 08:44 PM
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Aux heat and emergency heat are not the same.

The emerg heat setting on the t-stat disables the heatpump completely; in normal mode, the t-stat calls for aux heat as needed while the heatpump continues to run.

You might need the heat strips a couple of mornings per year, so the best option is to install a switch (on the wire connected to aux at the stat) in between the t-stat and air handler to enable the aux heat as needed.


Aux tstat--------->light switch----------->air handler
 
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Old 01-12-13, 08:48 AM
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I am running it in auto, set to heat to 71 and cool to 76 all day everyday.

I also need help with the outside unit. It freezes up. There is just one board. I only see two test pins on the board that say "speed up" underneath. The board was changed by a tech and it didn't fix the problem. Currently I have to run the system in cool to defrost the coil, then switch back to heat. It takes about a half hour for the coil to thaw.




 

Last edited by Hwy49er; 01-12-13 at 09:37 AM.
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Old 01-12-13, 11:13 AM
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Post the model number of this ~ 1984 heat pump so that we can view the manual.
Has it been 8 years since the defrost control was replaced?


You have a black wire on the top right terminal of your 2004 defrost control that is connected to a terminal labeled DFT.

Looks like the DFT closes to common when temperature falls below it's setpoint.

Is this normally open defrost thermostat securely clamped to the coil?

You can ohm it when it is submerged in ice to see if it closes on temperature fall.


 
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Old 01-12-13, 11:54 AM
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It has been two years since the board was replaced, I think.

If it is defrost t-stat is the one in the lower center of the second picture, it is tight.

So if you look at this picture you can see the DFT with a skinny black wire.

If I look at sensors in the unit (second picture), I see one with two skinny black wires (the one in the lower center of the second picture).

If you look at the first picture again there is only two skinny black wires. One on the DFT and one to the left of the DFT on C. If I probe the two skinny wires there is continuity. 25 ohm. Do I need to take he grate off unstrap the sensor and drop it in a glass of ice water?
 
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Old 01-12-13, 12:05 PM
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Looks like you already have ice in the picture. I wouldn't expect so much resistance with a closed circuit. Will it go into defrost if you jumper the 2 terminals that went to the DFT?

Can you make out the model number of the unit? I can probably post a link to the manual.
 
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Old 01-12-13, 12:17 PM
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Yep, that's ice. It was thick, covering everything this morning. My inside temp dropped to 64 with the Aux disconnected. I ran the unit in cool for 25 min to thaw everything. Switched back to heat and that ice is from about one hour. Last nights low temp was around 28-30.

The model number is 38qh03010.

Jumper the two skinny black wires? Should I do this when the outside unit is on or off. What indicates it is working?
 
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Old 01-12-13, 12:44 PM
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Your heat pump should go into defrost at the timed intervals that you have selected on the defrost control if the DFT circuit is closed. I see that the yellow wire is on the lower pin but I cannot read it.

I'll see if I can find your manual...
 
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Old 01-12-13, 12:54 PM
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That's the 30 pin. Pins are 30, 50, 90.
 
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Old 01-12-13, 12:59 PM
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Will it go into defrost if you jumper the 2 terminals that went to the DFT?
Jumper the two skinny black wires at the board? Should I do this when the outside unit is on or off. What indicates it is working (defrosting)? Will the fan be running? Will there be a different sound when I jumper it?
 
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Old 01-12-13, 01:18 PM
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http://www.docs.hvacpartners.com/idc.../38e,q-1sm.pdf

Your manual might help...

You will definitely hear when it goes into defrost. It will hiss as the reversing valve is energized and the large copper hot gas pipe to the house becomes the cold suction pipe with 1/3 the pressure.




 
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Old 01-12-13, 03:18 PM
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If you read 25 ohms across your DFT when it is closed and you measure 0 Ohms when you touch your test leads together (to prove that it isn't just your meter or leads causing this high reading) I am leaning toward a new DFT requirement.
 
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Old 01-12-13, 03:47 PM
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My mistake. I read 25 ohms with the wires plugged in. 0.1 unplugged. I saw my mistake when I read the troubleshooting guide you provided.
 
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Old 01-12-13, 04:04 PM
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Thanks for the manual. I have gotten part of the way through the steps. It says disconnect the fan. I unplugged the brown wire (picture) from the cap and taped it off. Does this look/sound right? I'm not 100% sure it sounds like it should. With heat on the fan isn't running and i guess it sounds like the compressor is running. I measure 24 volts at W2 and R.

Is it safe to run it like this for minutes?

I jumper-ed TP1 and TP2 but I don't think anything happened, just a lot of creaking sounds. It still measures 24v at W2 and R.

The pipe the t-stat is on reads 24 deg with a laser thermometer.

I am worried I about running it too long without the fan. Should I be? Did I unplug the right wire to disable the fan properly?
 
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Old 01-12-13, 04:12 PM
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That's not the right wire. It should be the black wire to the fan that is on the defrost control.
It is plugged into the black, plastic, square relay.
 
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Old 01-12-13, 05:23 PM
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Did it ever go into defrost mode?
 
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Old 01-13-13, 10:35 AM
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Sorry, I had a party to go to so I threw it back together for the night.

I woke up at 4 am and it was totally iced. 64 f in the house. I ran it on cool to 62 f to defrost the coil (about 15 minutes) and set it back to heat to 71 f. I went back to sleep. When I got up at 9 am it was totally frozen again. 61 f in the house. I think it ran all night. I think I am burning a lot of electricity because of this especially when the aux heat is plugged in at the house t-stat. I mentioned in the beginning that I had unhooked the aux heat. I assume this should have no relevance to the defrost problem since aux heat has been wired up 'till two days ago.

Still totally iced up, I pulled the black wire at the relay to disable the fan, pulled the t-stat wires from DFT and C (skinny black), jumper-ed the DFT and C on the board, checked resistance totally iced 1.8 ohm, 7 f on the pipe by the t-stat with laser thermometer. I set heat to 71 f in the house, jumper-ed the TP1 and TP2 and did not hear anything but the creaking of the coil and compressor whine. I measured 27 vac at W2 and R.

I think I'm going to hook everything back up, run it in cool to warm the coil up and check continuity to see if the t-stat goes open while I wait for opinion/suggestion.
 

Last edited by Hwy49er; 01-13-13 at 10:52 AM.
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Old 01-13-13, 11:53 AM
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You don't have to disconnect the outdoor fan unless you want to make ice. You already have ice so I would leave it wired in.

Disconnect the DFT from common and the DFT terminal and jumper across the two terminals. Place a jumper across the speed up pins and restore power. Give it a heating demand and the heat pump should go into defrost in less than 8 minutes.
Remove the speed up jumper as soon as it enters defrost.

If it never enters defrost you need a new defrost control.
 
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Old 01-13-13, 12:22 PM
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I defrosted the coil and checked resistance de-iced 1.1 ohm, 33 f on the pipe by the t-stat and 31 f on the t-stat with laser thermometer.

I read in the manual that the defrost should start within 30 seconds (troubleshooting step 8 towards the end). So I only waited a little longer then that.

I think that is a typo because prior to that in step 8 it is explained that jumpering the speed-up reduces my original time of 30 by 1/4. So I see where your 8 minutes comes from.

The air handler fan should be off during the defrost (cooling cycle) right? To prevent the inside temp from dropping during the reversal?

I did the DFT jumper from your last post, turned on heat, placed speed-up jumper and started a stopwatch. I waited 15 minutes and didn't hear anything.
 

Last edited by Hwy49er; 01-13-13 at 12:57 PM.
  #23  
Old 01-13-13, 12:56 PM
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I guess I have to make ice again and start over.
If you bypass the defrost stat, you do not need Ice.
If you have 1.1 ohms you don't even need to bypass the DFT.


The air handler fan should be off during the defrost (cooling cycle) right?
Nope. The indoor fan should be running. You should have a heating demand at the stat.

Can I break it by not running the fan along time?
2 minutes will not hurt anything but I'd leave the fan connected.

I think that is a typo because prior to that in step 8 it is explained that jumpering the speed-up reduces my original time of 30 by 1/4. So I see where your 8 minutes comes from.
I'd wait a little over 8 minutes before spending any money on a new defrost control.
 
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Old 01-13-13, 01:03 PM
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I did the DFT jumper from your last post, turned on heat, placed speed-up jumper and started a stopwatch. I waited 15 minutes and didn't hear anything.

If when it is in the defrost cycle (reversed/cooling) during a heating demand, wouldn't it cool the house with the air handler fan on? Or are you saying that it uses aux heat to offset (by mixing cold and hot) to counter the cooling effect of defrost cycling? I guess I am assuming that cold refrigerant is flowing through the coil in the air stream in the air handler. Or is the coil bypassed via a valve during a defrost cycle?
 
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Old 01-13-13, 01:13 PM
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Or are you saying that it uses aux heat to offset
Yes. It closes the R (24VAC power) wire to the W2 (electric heat) wire as shown in figure 11 and switches the reversing valve to the cooling position to defrost.

You need a new defrost control.
 
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Old 01-13-13, 01:21 PM
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Should the aux heat still get the call from the outside unit and work even with the inside t-stat aux is unwired? The inside t-stat aux is a separate call if the set point and current temp are too different right?
 
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Old 01-13-13, 01:26 PM
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Should the aux heat still get the call from the outside unit and work even with the inside t-stat aux is unwired?
Yep and Yes Aux heat inside is separate.

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Old 01-13-13, 01:31 PM
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You da man! Thanx for being there and hanging in. Thanks for the link. That would have been my next question.
 
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Old 01-13-13, 01:38 PM
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Turn off the breaker(s) for the indoor unit and the breaker for the outdoor unit before replacing that defrost control.

70 bucks is a cheap fix. I would charge $99 to ring your doorbell on a service call.
 
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