heat strips.. T stat or defrost board? How to test

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  #1  
Old 12-20-19, 10:38 PM
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heat strips.. T stat or defrost board? How to test

2 TON 2 STAGE TEMPSTAR heat pump. 5kw heat strips. T6 pro t stat honeywell. 700cfm system

Trying to find out how the heat strips operate in regards to t stat and/or defrost mode.

Heres my two scenarios.

1. options in ISU #253

aux/E terminal control
0- drive both aux and E together
1-Aux and E independent

This is set on 0. fan blows very high and it seems heat strips work but air not hot due to fan speed. seems fan in blowing max 1200 cfm.

set to 1, ( which it was on last year but installer changed this year due to no heat strips working this year) It will blow at the lower stage fan it seems but only blows cold air.

2. Set to 0 the heat strips do not come on with defrost mode. Defrost was on this morning for about 7 min and only cold air.

anyone know what the settings in the t stat should be#253?

What can we assume is the issue?
 
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Old 12-20-19, 10:48 PM
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Mike.... usually the heat strips are activated by one wire. Typically it's the white one.
Many times there are two wires run to the stat...... one for AUX and one for E but both are connected together at the air handler end. I can't see the advantage to having the heat strips activated separately.

Do you know if your heat strips have sequencers in them ?
Usually a sequencer will be setup to start the blower on low speed and then turn on the coils. If that is the case..... you'd set the stat to not turn on the blower with the heat strips but allow the sequencer to do it.

The sequencer will run the blower in low speed while activating the G terminal at the stat will run the blower at high speed.

The same white wire gets activated from the defrost board too.
 
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Old 12-20-19, 11:53 PM
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IDK pete im not an HVAC guy..

Its one wire I believe..E...

No sequencer. Its a single 5kw
 
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Old 12-21-19, 12:07 AM
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Old 12-21-19, 12:09 AM
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Old 12-21-19, 12:10 AM
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Cant turn pic...............................
 
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Old 12-21-19, 11:34 AM
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You have the white wire on AUX. So technically setting 253 doesn't come in to play as that is if you use both an AUX wire and and an E wire. You're using one wire to do both.

You need to see what happens when you just power the white wire. If powering just the white brings on the heat strip and the blower on low...... you need to change when the blower comes on. It's currently set to come on in high mode on a call for heat.
 
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Old 12-21-19, 02:00 PM
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Amped the strips on em heat.. 20 amps.

shorted pins to activate 30 second defrost.. 24 volts at white and 20 amp draw at strips. all working.

before testing:

White wire at board on air handler was flaky. Stripping of wire was bad and original installer pushed it up the screw too far. I dont think it was making contact with the board at air handler.

also I would think 22f here in SC that night in defrost when I noticed cold blow, a 5kw strip against a cold coil may prove a break even duct temp.

700 cfm unit and 725 cfm when heat strip on. Cant slow it down any because board at air handler produce same CFM at the two settings of C and D on the board.

Figure 21 shows setting D @ 625 CFM for a 0-5kw heater.

But table 4 shows 725CFM when set Nominal, Which it is set for..

Conflicting...hmmmmm

It would seem setting C or D for KW size will produce the same 725CFM. Although the CFM adjust chart suggests 625 CFM min.

I would think they are talking as if I adjust fan speed to low that will produce 10% less.

725-10%= 650 cfm.. wtf..



https://www.utcccs-cdn.com/hvac/docs..._ICP_25652.pdf
 
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Old 12-21-19, 02:17 PM
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This seems the proper setting as the other does not allow heat strips to come on and fan speed is super slow..

0- drive both aux and E together
 
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Old 12-21-19, 02:52 PM
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0- drive both aux and E together
You don't have an aux and E wire so that shouldn't make a difference. The difference is in how the blower is controlled. That setting may allow the heat section to set the heating fan speed.

If the thermostat controls the fan...... it's going to be on high.
 
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Old 12-21-19, 10:26 PM
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Equipment controls fan.. there is no setting in t stat to control.

But ICU 253 does make a difference..
 
 

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