Where are AUX or EM coils/strips located and does my system have them?

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Old 12-01-13, 11:26 AM
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Where are AUX or EM coils/strips located and does my system have them?

Hi,

New to HVAC beyond simply installing new thermostats.

Last night I noticed that my Trane system (with Honeywell RTH7600 thermostat) would blast cold air about ever 20 minutes for a duration of 3-5 minutes and then return to heat. The outside temp was about 20 degrees and I assume that this was occurring when the system was defrosting.

I also noticed that it does not seem that my system is any warmer when the AUX indicator is on.

This led me to assume that my electric heating coils were not working so I switched the system to EM heat and there was no warm air at all (air about 60 degrees was coming from vent).

I then went so far as to manually twist the R, G (blower), W (AUX), and Black (X2) together and again, no warm air.

This lead me to assume that either my electric coils/strips are bad or... I DON'T HAVE ANY... but I have no clue where to look for them or how to test them.

My system is as follows:

Outside = Trane XB10 2TWB0024A1000AA
Inside = Trane TVF024A140A1
Thermostat = Honeywell RTH7600

Wiring:

Wire color (old thermostat label) ---> Terminal
Blue (B) --> C
Green (G) --> G
Yellow (Y) --> Y
Orange (O) --> O/B
Red (R) --> R (jumped to RC)
White (W) --> AUX
Black (X2) --> E

Programming:

Function --> setting

170 --> 7 (heat pump with backup or AUX heat
180 --> 1
190 --> 0 (cooling changeover. confirmed by hot wiring O to RYG bundle and getting cold air)
270 --> 9 (but will be setting to 3 as many state that this cycle rate setting is better)

So... Do I even have AUX or backup heat? If so, how do I test coils/strips to see if they are good or not?

Thanks.

Greg
 
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Old 12-01-13, 11:31 AM
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If you don't have any type of fossil heating system then you do have electric heating coils.
They can be found inside the air handler.
 
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Old 12-01-13, 11:43 AM
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Ok. Then I assume that they are in the top of the Trane TVF024A140A1 unit.

Seeing I do not seem to be getting anything from them in EM Heat mode, I assume that they are bad. Is there a way to check them?
 
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Old 12-01-13, 11:54 AM
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I'm trying to find the manual for your unit.

The HVAC pro Houston will also be checking in.
 
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Old 12-01-13, 11:59 AM
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Remove the panel a take a picture of your heat strips.
Post a picture on the site using Photo and image hosting, free photo galleries, photo editing

I may be able to give you some points to measure for voltage or ohms.

This is a Carrier example. Your strip will not have a sequencer...
 
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Old 12-01-13, 12:15 PM
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Photos here:



 
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Old 12-01-13, 12:29 PM
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And thanks...

and thanks for the help on this... you're saving me a ton of time, frustration, and probably money!
 
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Old 12-01-13, 12:35 PM
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When an emergency heat demand is present...
Do you get 240 volts AC when you place your leads at A?
Do you get 240 volts AC when you place your leads at B?
Do you get 24 volts AC or 22 volts DC when you place your leads at E?

This is high voltage. Be careful.
 
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Old 12-01-13, 12:38 PM
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Thanks for putting this together. My meter is in my storage unit and I will go get it tomorrow (possibly tonight) and run the tests.

Just for clairification: should I just set the thermostat on EM heat when I do this or simply crank the temp up to trigger the aux?
 
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Old 12-01-13, 12:44 PM
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You can drop out your heat pump on high head pressure if you only crank up the heat. Since you would be allowing air to bypass the indoor coil it would be like running the outdoor unit in the summer without a condenser fan.

I'd check as much as possible in emergency heat mode first.

You could turn off the outdoor unit disconnect for testing and eliminate the risk of high head pressure lockout , but if it is a Square D breaker type service disconnect, it might not turn back on.
(I never understood how they can make good breaker panels and the worst service disconnects that I have seen.)
 

Last edited by Houston204; 12-01-13 at 01:10 PM.
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Old 12-01-13, 12:51 PM
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If you have a clamp meter you can grab one wire on A to look for ~ 20 amps then grab one wire on B for ~ 20 amps. If you have 20 amps on each strip, they are working.

 
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Old 12-01-13, 01:02 PM
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If you are getting 240VAC at A and at B and are not getting heat, Remove power, unplug the 2 wires on A on take an Ohm reading across the 2 terminals that your A wires were connected to.

This Ohm reading should also be taken at B.


Remember to Turn Off Power for this test.
 
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Old 12-07-13, 10:30 AM
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Sorry that it has taken me this long to reply...

When I press the probes to the connections indicated in A or B I get nothing. If I touch one of the probes to one of the leads and then to the surrounding metal I get 124V.

I have no idea what this means or what to do next.

I don't have clamp meter.
 
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Old 12-07-13, 10:34 AM
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I do get 24V at E but nothing at A or B
 
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Old 12-07-13, 10:40 AM
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The A set of terminals is one element and the B set of terminals is the second element.

You checked from one terminal to ground and saw 120v. Then you checked both terminals to each other and found nothing. That means you have lost one leg of your 240vac supply. You need to go back to the disconnect and check for 240vac there.
 
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Old 12-07-13, 10:41 AM
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List the readings at C,D,F,G and H.
If you are getting 24 volts to the heating relay and do not get 240 volts to the heat strip, we should find the location that power stops.

C will tell you if you have 240 volts to the air handler.
 
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Old 12-07-13, 12:24 PM
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Will do. I have a wife and two kids so finding a solid block of time is nearly impossible. I'll post the readings by the end of the weekend.

I did the earlier tests with em heat on and the hp switched off at the breaker just in case... I also tried craving the heat up with the system in normal heat to trigger aux (again with hp off) and sane readings...
 
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Old 12-09-13, 10:58 AM
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A = 0 (120 when grounded)
B = 0 (120 when grounded)
C = 240
D = 240
E = 24
F = 240
G = 0
H = 0
 
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Old 12-09-13, 11:02 AM
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What do you mean, "go back to the disconnect and check for 240 there"? How/where do I do this?
 
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Old 12-09-13, 04:59 PM
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If D and F each have 240 volts you have potential energy here.
If each of these relays have 24 volts to them and read 240 volts at D and F it points to faulty relays.

It's hard to believe that both of them have failed, but that's what the readings point to if they each have 24 volts to the low voltage terminals.
 
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Old 12-10-13, 05:44 AM
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So what are the relays and how do I replace them?

Is there any way to, or should I, check that the heat strips are good?
 
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Old 12-10-13, 08:09 AM
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The blue circled items are the safety stats.
The yellow circled items are the relays.
The red circled items are the heat strips.

You can turn off power to the unit. Remove the wires from the heat strip and check with an ohmmeter. Should show almost a dead short.

You'll notice in the picture 3 devices labeled A and three labeled B. There are two separate heating sections here and very rarely do they both fail at the same time.

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  #23  
Old 12-10-13, 09:05 AM
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So a dead short means ohms of 0 or nearly 0? And this is good?

Should the relays both be on in EM heat and/or aux heat?

Yesterday I noticed no voltage to these in either case. I did brush up against the red wire going into heat strip on the right and got a hell of a buzz so I know that there is power.
 
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Old 12-10-13, 09:10 AM
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Basically any reading on the meter is good. Those coils are usually open or normal.

When in EM heat.... both relays should have 24vac on their coils and they should be closed.
 
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Old 12-11-13, 04:50 AM
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If there are two heat strips, does it mean that one is active in AUX mode and both in Emergency?

Before i look into replacing the relays, should i go ahead and remove the thermostat and tie the R, W, G and and then R, W, G, and X2 wires together in a last ditch effort to see if the it is a bad thermostat rather than bad relays?

My understanding is that W is AUX and X2 is emergency (G is the blower and I'd add that in to see if there is heat coming from the vents). My assumption is that if I tie these together, then the relays should work. If they have 24v but there is still no heat, then perhaps just the coils are bad? If I tie them together and there is no voltage at the relays, then they are bad and need to be replaced?

If the relays are replaced, these are just the little removable, 24v pieces to the right of formerly labeled items D and F?

Finally, IF this system was working properly in EM heat, what should the below voltages read?

Item = What I have now --> What they should be
A = 0 (120 when grounded) -->
B = 0 (120 when grounded) -->
C = 240 -->
D = 240 -->
E = 24 -->
F = 240 -->
G = 0 -->
H = 0 -->
 
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Old 12-11-13, 08:25 AM
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A = 0 (120 when grounded) --> measuring A to A > 240vac
B = 0 (120 when grounded) --> measuring B to B > 240vac
C = 240 --> 240vac
D = 240 --> 0v
E = 24 --> 24vac
F = 240 --> 0v
G = 0 --> 0v
H = 0 --> 0v

Since you are measuring 240v on D and F it means the relays are open and at this point the elements are good.

All your voltage measuremens above should be made to both letters..... not from one letter to ground.
 
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Old 12-12-13, 05:05 PM
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I just had that power off to everything and pulled the connections to the coils at A and B. I got around 11 ohms at each point so I assume that the coils are good?

G and H also get around 1 ohm.
When the EM heat was running, I still have nothing at A to A or B to B.

E had 24vac however I pulled the piece that the blue and orange wire are running into it at E (the delay?) and tested the prongs that connect into the base part that is attached to the heater (the relay?). There was no voltage coming off of the "back" side of the delay. Is this normal or is this the part that needs to be replaced? Or is it the "base" part... the DC relay (Warren eStore)?

If this is not what needs replacing, what does? Where is the power being stopped?

Thanks.
 
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Old 12-14-13, 10:21 AM
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11 ohms on both heating elements is good.
1 ohm or less on the stats is good. (G & H)

To answer a previous question.... since there is only one set of wires feeding both relays..... they both come on together.

Ok.... those two parts you are asking about, and I have circled in yellow in post 22, are high current control relays. You won't measure voltage coming from the relay.... the furnace applies 24vac to the orange and blue wire and the relays close.

So if you measure 24vac on those two wires when they are connected to the relays and they don't close supplying 240vac to the elements.... then they are bad.

Are there any parts numbers on the relays ?

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Last edited by PJmax; 12-14-13 at 10:53 AM. Reason: added diagram
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Old 01-01-14, 10:30 AM
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Happy New Year!

Sorry for taking so long to reply...

The parts are:

1) Warren Tech CCR9-5
2) ORG T9CPID52-22 N.O. 30A. 240VAC. 02371

Should I replace both parts?

Thanks,

Greg
 
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Old 01-08-14, 05:57 PM
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I went ahead and replaced both the parts for each coil. Even though it was probably just bad relays and not the rectifiers, I replaced those too as they were so inexpensive.

Good news is that the coils come on when aux kicks in and has been a huge help.

Bad news is that I still get cold air during defrost and when I switch the system to EM heat. My Stat has the white wire connected to aux terminal that connects to the coil controls in the air handler. The black X2 wire is in the E terminal. This wire is tied to another black wire in the handler and this second black wire appears to head out to the HP and send the signal to turn it off (I assume).

Somewhere the system is not telling the coils to come on in EM mode or during regrowth.

Any thoughts?
 
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Old 01-08-14, 06:08 PM
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Do you have a jumper between Aux and E at your air handler?
 
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Old 01-08-14, 06:12 PM
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No jumper between aux and e in Stat or between white and black wires in the handler.

Would jumping any of these together cause the HP to turn off even when just an Aux call comes from the Stat?
 
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Old 01-08-14, 07:18 PM
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I would jumper Aux to E at the air handler since you only have 2 elements.
 
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Old 01-09-14, 12:53 AM
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So to do this I should just add a short wire between the wire wires and the black where they enter/exit the handler?
 
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Old 01-09-14, 04:53 AM
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Yes, install a short piece of wire as you have described.
 
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Old 02-16-14, 11:38 AM
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I added the wire and now the emergency heat works properly. It also seemed to fix the cold air during defrost mode too.

Thanks for all the help. The system is now up and running really well!
 
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