Question about Heating & Cooling

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The output side of the 24-volt power supply transformer on my Tempstar shorts when the thermostat is switched to "Cool". No problem on heating mode. I've burnt a couple of transformers before I inserted a 5 amp fuse in the output side circuit. I've shorted a few fuses since, so I don't even try switching to cool mode anymore. At first, it would run on Cool mode for a few seconds before shorting. The last time though, it just burned the fuse instantly. Should I just replace the control board?

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  • mdleqz Jun 06, 2010

    Doesn't disconnecting the wires that go outside break the cooling control circuit? How will that conclusively tell me that the control board is bad if its components are not energized? Is the control board completely a separate circuit, operating the ACCU with solenoids?

  • mdleqz Jun 06, 2010

    How can I tell with absolute certainty whether or not I need a new control board for my Tempstar HVAC unit? And if I don't, can I lick this problem by running a completely new set of control wires from the board to the ACCU?

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2 Answers

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  • Contributor
  • 857 Answers

That sounds like a good idea if it has already happened to you many times, changing the control board will fix the problem completely.

Posted on Jun 06, 2010

  • 1 more comment 
  • mdleqz Jun 06, 2010

    Hi. Do you say so after reading the bit of background I provided, completely agreeing with the last service guy who was here? Don't you have any idea on how I can absolutely make sure it's the control board that I need to replace? They cost upwards of $300, and they do not take returns.

  • Jayant Jha Jun 06, 2010

    Yes i understand that, it costs much but yes temporary repairs will continue to cause you problems, You can decide what to do..?

  • Jayant Jha Jun 07, 2010

    If you wants you can give a try that may help or may-not..!!

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  • Master
  • 8,220 Answers

Check outside for chewed up wires.

Posted on Jun 06, 2010

  • 12 more comments 
  • Dan Webster
    Dan Webster Jun 06, 2010

    A transformer will die quickly if wires are touching.
    Look for breaks in the wire from weed eater or animals.

  • Dan Webster
    Dan Webster Jun 06, 2010

    A control board would blow. Diconnect wires to outside and see if that fuse still blows on cooling mode.w fuse in heating and cooling if it was bad.

  • Dan Webster
    Dan Webster Jun 06, 2010

    A control board problem would show up in both heat and cool modes. You have a shorted wire.



  • Dan Webster
    Dan Webster Jun 06, 2010

    Disconnect wires going outside and see if that fuse blows and that will let you know the board is bad. Then trace down the broken wire.

  • mdleqz Jun 06, 2010

    A local service guy did that around and inside the ACC unit last time and did not find anything. He thinks the part of the control board that supplies power to the cooling controls is fouled.

  • mdleqz Jun 06, 2010

    Maybe a little more background will help: I have completely separate dual units that only share the distribution air duct. This unit is the only that has had this problem. The very first time this happened, the service guy replaced the transformer. It lasted the whole season. But the following summer, the transformer burnt up. I replaced the transformer and it did not last the whole summer. That's when I called in the last service guy who basically bypassed one of the wires from the control board on the hunch that it was fouled somewhere hidden between the control board and the ACCU. That worked for a few hours the first time. But I had to call him back when the fuse blew again. It seemd that as the unit ran and the day got hot, the fuse would blow. That's when he suggested I consider replacing the control board. Meantime, I invested on a few fuses, until the last time, the fuse instantly blew. It was nearly fall, so I put off dealing with this headache. All winter and spring this year, the heater worked, no problems. Now that it's summer again, I need to have it fixed.

  • Dan Webster
    Dan Webster Jun 06, 2010

    How far is the run between the controls and the unit? You may need a stronger transformer maybe a 75va with a re-set button on it. If the wiring is pretty far away you need to increase the volt amps. Sorta like using an ordinary water hose to put out a 10 story house fire you need more volume. What you have now is probably a standard 40va 24 volt transformer. You probably need to step that up if the wiring is good(no short) but the distance between the control and the unit is great.

  • Dan Webster
    Dan Webster Jun 06, 2010

    You need to consult other pros on this. I sold HVAC equipment for years. I am retired now. If that transformer is burning up it is because of a short or it is over worked. Good luck to you sir.

  • Dan Webster
    Dan Webster Jun 06, 2010

    If you disconnect the wires from outside and then turn on the ac and fuse still blows then YEAH you need a control board, but if it don't then you need to find the shorted wire or run some new stuff. Disconnect the wires inside and go outside. Check for continuity outside. Sould not be because you disconnected the wires right?

  • mdleqz Jun 06, 2010

    I'll try what you said about disconnecting the wires outside. I see now that If the fuse blows, that's a positive indication the control board is bad. But if it doesn't, it does not necessarily mean the control board is good, because the part that's bad may not show when the wires outside are disconnected. Am I correct in thinking this? If the fuse blows, then we're sure the board is bad. If it doesn't, then we're not sure the board is not bad. If so, what next? Please bear with me because I only know HVAC systems just a little better than the lay person. I don't really know how their control circuits are wired.


    (About your suggestion on transformer rating: the last transformer I bought was a 75 va with a reset button. The conductor run is about 30 to 35 feet from the attic of 2-story house to the ACCU on the ground just outside on the same side of the house. Is it possible that the insulation between a paired (?) wire somewhere started to break down over time until the wires became fused?)

  • Dan Webster
    Dan Webster Jun 06, 2010

    A critter of some sort could get into the wiring, the wires are small to begin with, age or wiring could have something to do with it. If you disconnect the wires at the control board and disconnect them at the unit you should have a no continuity between the wires correct? If you have continuity that woul mean them wires is shorted somewhere in the run.

  • mdleqz Jun 06, 2010

    Hi. I went outside to disconnect the wires, as you said. But I saw that wires were connected differently from the other ACCU that was running. I think the last service guy did that. So I decided to copy the connections in the ACCU that's working. Then I turned the thermostat to COOL and the fan to ON (instead of AUTO). The FAU turned on, but the ACCU never kicked in. That was at about 7:30 this morning. The FAU was still running when we left at 9:15, but coming back at 1:30 PM, I found that power to the thermostat (green pilot light) was out.


    I'll go get some fuses and then disconnect the wires at both the ACCU and the control board. Can you tell me which wires those are, just to be sure? Are those the red and white pair in the brown jacket that comes out of the building with the cold refrigerant line (bigger diameter tubing)? It's about the same size as a water sprinkler control cable, but with only two wires? At the control board end, would they be the only red and white wires there? If I find there's continuity (therefore, they're shorted somewhere, they're not the kind that are run in a conduit that I can just thread with a replacement pair, right? I'll just have to string a new 2-wire cable from the board to the ACCU any way I can, yes? Thanks.

  • mdleqz Jun 06, 2010

    Hey, Mr. Mobilian. If you're monitoring this, let me tell you that I observed ice on the cold line of the other ACCU that's running. That's not normal, right? Is the ACCU not getting the right signal from the thermostat? I also noticed that even on AUTO, the unit (FAU and ACCU) run for very long periods and never reach the set temp of 78 F, only 83 F. I think they stop running only when the Edison-installed energy monitor cuts the power. What do you suggest I do? Thanks.

  • Dan Webster
    Dan Webster Jun 06, 2010

    Seems to me you have a dirty condenser of maybe an incorrect freon charge. The low side pressure should be about 68.5 PSI. I don't know from sh!t which wires should be where because I would need to see for myself. I am thinking you need a pro to look over the connections. You should only have 2 small wires going out to the unit to power up the contactor. You should have 2 wires sending out 24 volts from the board. It ain't that complicated. If you have transformers burning up then that means you have a short or a wire run that is too long.

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1 Answer

Thermostat fuse keeps blowing


The fuse protects the transformer from being damaged due to too much amperage, this is typically due to the circuit having a short or a device in that circuit being shorted.
See below the transformer's relationship to the thermostat.
The RED wire is the "hot leg" of the 24 volt power provided by the transformer to the thermostats R or RED terminal as pictured below.
The 24 volt hot leg enters the thermostat on R or RED.
The various other terminals White = heat, Yellow = cool ,
Green = fan and Common is the side of the 24 volt power source that every 24 volt circuit terminates or return to complete the circuit.
Thus the common name designated, note hoe everything returns to Common.
Well if we jumped Red directly to Common that is a short and will blow the fuse as you observe.
See the 2 diagrams in red describing a notrmal circuit then a short circuit.


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25510598-olwf3gt1n1i2ofytj5fivkso-4-2.png

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Mar 03, 2015 | Heating & Cooling

Tip

How to wire your new themostat


0a9962f0-eea8-41fa-881b-a1074d6aa966.pngThe heater has a transformer that steps down the line voltage supplied either 115v or 230v to 24 volts,a safe voltage to use for the thermostat's control voltage and a voltage which requires no license to install.
The most important thing to remember before you begin is that ,
Red or R is the "hot leg" of the 24 volts provided by the transformer and
Common or C is the "neutral leg" of the 24 volts provided by the transformer and
Common is the side of power which EVERY 24 volt circuit will terminate or return to in completing the circuit, thus the "Common " designation, note after each circuits device, be it AC or Heat or Fan,every 24 volt circuit returns to Common or it's circuit is not completed.
Every electric circuit ,regardless of voltage or polarity requires a device ,
without a device in a circuit, upon energizing that circuit it will be a direct short!
Red to Common, this will blow the fuse or worse the transformer if not protected by a fuse which some are not. If you have a device in the circuit you can energize a circuit, my point being do not let Red touch Common and as Common is grounded at the transformer, do not let Red touch any metal, as it is likely grounded too, so turn off power before doing anything.
Note the color of the wiring attached to your existing thermostat's terminals and make a diagram so you will not forget.
The new thermostat may have different terminals or more that you will not be using.
All thermostats have an R or Red terminal, it may be RC and an RH 2 separate terminals designating RC as red cool and RH as red heat.
There 2 terminals RC and RH are for 2 transformer systems which are obsolete old GE units so if you do have both RC and RH use a small jumper wire and connect the 2 terminals and wire the Red "hot leg" from the transformer to either RC or RH it will not matter if both are jumpered together, otherwise you will only have cooling or heating but not both available.
The Red hot leg of the 24 volts enters the thermostat on R and most modern thermostats are parasitically powered meaning they derive power from the heaters transformer, as a result the Common 24 volt neutral leg must be ran to the thermostat.
Note, the new NEST thermostats say they do not require Common to be wired, however 50% of the time the NEST will go dead in time and require a Common wire be used to power the thermostat satisfactorily.
Upon a call for heat the switch between the Red and White circuit closes making white electrically hot with the 24 volts which it sends out the white wire to the heater gas valve etc and return to common to complete the heat circuit.
Upon a call for AC the switch to Yellow closes and as you will notice the Fan switch on the thermostat has an AUTO and ON switch, in the AUTO position, upon a call for AC
the Yellow becomes hot with the 24 volts and as a result of the AUTO switch being closed, the indoor blower will automatically cycle as required.
The fan control for ON fan or AC is High speed, the fan control for heat is Low speed and controlled by a time or temperature delay at the initiation and termination of the heat cycle, this is to eliminate cold air from blowing until the heater warms up and upon termination it extracts the residual heat to not overheat the unit and be most efficient.
Green is the Fan circuit, it is the High speed fan and only used for heating with electric heaters as resistive heat strips or heat pumps and will be controlled in both heat and cool modes by the thermostat, this is designed in to the thermostat or part of the thermostats set up and programming if a universal type thermostat.
Common as explained is there to power the thermostat it being the other side of 24 volt power opposite from the red 24 volt hot leg.
Heat pumps will have an O and a B terminal, this gets the Orange wire on O if the reversing valve is energized in cool mode, if you get heat in the cool mode switch the Orange wire from O and put it on B, B is energized in the Heat mode.

This was not written for just heat pumps or any brand I had to pick a specific brand however this applies to all brands and types gas furnaces , heat pumps and electric heat.

on Oct 13, 2013 | Aube TH144HPN2H1C Thermostat: Heat-Pump...

1 Answer

Why won't the compressor run


This can be for a variety of reasons. It ranges from something as simple as no supply power (blown fuse, open breaker, faulty contactor, or run capacitor) or it could be more serious as a grounded or open winding in the compressor motor. My suggestion to any novice and or person without proper tools and knowledge; First check the low voltage (24 volt control voltage) by turning on the "Fan on" switch located on the thermostat to on, not "Auto" The blower fan should come on, indicating there's 120 volt and 24 volt available. Fan doesn't come on is an indication that there's no control power. The next step would be to check for power at the transformer and fuse located in the air handler. There should be 240 volts feeding the transformer, and 24 volts coming out. The control voltage is needed to operate the thermostat (which is the switch that sends the 24 volt signal to the compressor contactor to turn the compressor on/off. This 24 volt also powers other relays and switches in the system. knowing that 24 volt is available also tells you that the problem is most likely in the condensing unit (outside, where the compressor is located). At the condensing unit you should check for 240 volt supply power. Upon finding 240 volt supply power the question now becomes whether or not the thermostat is calling for anything (cool or heat if the unit is a heat pump). There should be 24-30 volt available at the small gauge wires feeding the contactor coil. While having the thermostat set at a temperature lower than the current room temperature (in the cooling mode) the thermostat should send a 24 volt signal to close the compressor contactor and turn it on. The non-metallic end of a screwdriver can be used to depress the moveable part of the contactor. After pushing in the contactor, should the compressor start then you may only need a new contactor. It may just hum because of a faulty run capacitor or grounded or shorted internal motor windings (grounded or shorted windings are usually indicated by tripped circuit breaker and/or blown fuse). It's a good idea to have a good multi-meter and knowledge of use before attempting any repairs or diagnosis on your own. I recommend some basic knowledge of electricity before even thinking about attempting any repairs or diagnosis.

May 08, 2014 | Goodman Manufacturing Goodman GSC130421...

1 Answer

Air conditioning thermostat not functioning


ab302475-b998-41c7-9c7c-4e106b68e0be.pngGo to your thermostat and look at the FAN switch, it will be in the AUTO position typically.
Set the FAN switch to the ON setting,
by doing this if the fan motor operates you know that the High voltage & the low voltage (24 volt control power) are present.
This saves you from having to go to the breaker panel and checking / resetting the breaker as well as checking the Transformer and automotive type 3 amp control circuit fuse (generally on the circuit board).

If you do not get any fan operation by switching the fan switch to the ON setting, you then will have to determine if the breaker, transformer and aforementioned 3 amp fuse are all good.

You will need a volt meter to test further.
At the thermostat remove the cover thus exposing the thermostats sub base and assorted circuits/wiring.

RED or R
Red is the 24 volt "hot leg" of 24 volt power which originates at the transformer. Red enters the thermostat on the Red or R terminal, some thermostats will have an RC and an RH terminal, these are jumpered together on single transformer systems as they are for Red Cool and Red Heat, without a jumper wire on RC and RH, the Red "hot leg" of the 24 volt control voltage will only energize the terminal its wired to, some stats are battery powered and do not use the transformers 24 volt power (parasitically) to power the thermostat.
If the thermostat is powered by the transformers 24 volt power, there will be a "COMMON" wire on the common terminal of the thermostat, this is the other side of the 24 volt power from the transformer, the side opposite from RED the 24 volt "hot leg"
Common is called common as its the side of power that EVERY
24 volt circuit terminates, or completes its circuit, thus the COMMON designation.
During a Heat call the 24 volt hot leg is sent out via the white/heat terminal to the gas valve etc.
So between terminals Common & White , it should read 24 volts during a call for heat.
Same for Fan which is the Green or G terminal,
Same for Cool which is the Yellow or Y terminal.
If you have no power to these terminals when calling for heat or cool or fan then yes the thermostat is defective and requires replacement.
DO NOT let the RED wire touch ground or the COMMON terminal, this is a direct short and blows the fuse or transformer
if not equipped with fuse protection.

Normally you should read 24 volts between RED and COMMON

Aug 01, 2013 | Goodman CKL36AR36 Air Conditioner

1 Answer

Wiring diagram for Thermoking V700MAX


Red or R is the "Hot leg" of the Transformers 24volt supply,
Common or C is the "Neutral leg" of the Transformers 24 volt supply;
and the side of power to which ALL the 24 volt control circuits
terminate to complete the circuit, example; Heat=W, Cool=Y, Fan=G.
Upon a call for heat a switch closes betwen the Red and White Thermostat terminals.
The stat sends the 24 volts to White or W for the heat circuit on W on the
furnaces LVTB low voltage terminal board.
Yellow or Y goes from Thermostat to furnace Y on LVTB, which is simply
a connecting point on its way to the AC units 24v contactor coil located outdoors.
It actually isnt even attached to the furnace many times as it serves no purpose there and simply
continues to the AC unit with the copper lineset that the AC unit feeds.
The remaing 24 volt Thermostat wire goes back to common on transformer to complete the Yellow
24 volt control circuit.
Green or G exits the Thermostat and connects to G on LVTB for the fan relays 24volt coil
and returns to Common to complete the Green 24 volt control circuit.
O is for a Heat pump reversing valves 24 volt solenoid, and return to Common as all 24v circuits must to terminate or complete the circuit.
Some parasitic type Termostats need the 24v power to run, some are battery, some are both.

Nov 01, 2010 | Heating & Cooling

1 Answer

Tempstar furnace when the thermostat is fan on the fan from the air compressor turns on not the air circulation fan in the bottom of the furnace


Y or yellow and G or green are connected in the "auto" setting, as G is fan and Y is cool, the Y and G wires are somehow, energizing the Y wire that goes to the AC unit to run cool, take thermostat off exposing the thermostats sub base Y and G will be there along with R, red, 24volt ("hot leg" of 24 v power) W white= heat, and C common, 24 volt ("neutral leg" or "common" leg of 24 power) common is where all the various 24 volt circuits (cool, heat, fan,) terminate or return to complete the circuit, just as a AA battery nas a positive and negative side of power, so does the furnace and all electrical circuits, its common as all circuits terminate there , its the opposite side of power fro whish all circuits begin, red is the :hot leg" and enters on RED red to WHITE=HEAT

RED to YELLOW=COOL
RED to GREEN= FAN

auto =Y & G connected
on= R & G connected

if you jump red to green, which is fan on, no connection should exist to yellow in on ! only auto!

May 27, 2010 | Heating & Cooling

1 Answer

I tring to change thermosat I can not remeber what color go where


Typical Thermostat Wiring for 4 or 5 wire Heat/Cool Thermostat (not heat pumps)
4 Wire Termostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
with one transformer for both units
Rc One Side of 24 volt Transformer
Rh Jumper Rc to Rh
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
With 2 transformers one for indoor unit
And one for outdoor unit
Rc = Red One Side of (outside) 24 volt (outside transformer)
G = Green Blower (outside transformer)
Y = Yellow Cool (outside transformer)
Rh = Blue One side of (inside) 24 volt (inside transformer)
W = White Heat (inside transformer)
COOLING ONLY Thermostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
HEATING ONLY
R or Rh One Side of 24 volt Transformer
W = White Heat

Feb 09, 2010 | Heating & Cooling

1 Answer

How do you wire a honeywell round mechanical thermostat


What are you trying to wire up?
Typical Thermostat Wiring for 4 or 5 wire Heat/Cool Thermostat (not heat pumps)
4 Wire Termostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
with one transformer for both units
Rc One Side of 24 volt Transformer
Rh Jumper Rc to Rh
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
With 2 transformers one for indoor unit
And one for outdoor unit
Rc = Red One Side of (outside) 24 volt (outside transformer)
G = Green Blower (outside transformer)
Y = Yellow Cool (outside transformer)
Rh = Blue One side of (inside) 24 volt (inside transformer)
W = White Heat (inside transformer)
COOLING ONLY Thermostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
HEATING ONLY
R or Rh One Side of 24 volt Transformer
W = White Heat

Feb 09, 2010 | Honeywell CT87B ROUND HEATING&COOLING...

1 Answer

I have a coleman Evcon model AH16-0 . I am


Typical Thermostat Wiring for 4 or 5 wire Heat/Cool Thermostat (not heat pumps)
4 Wire Termostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
with one transformer for both units
Rc One Side of 24 volt Transformer
Rh Jumper Rc to Rh
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
With 2 transformers one for indoor unit
And one for outdoor unit
Rc = Red One Side of (outside) 24 volt (outside transformer)
G = Green Blower (outside transformer)
Y = Yellow Cool (outside transformer)
Rh = Blue One side of (inside) 24 volt (inside transformer)
W = White Heat (inside transformer)
COOLING ONLY Thermostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
HEATING ONLY
R or Rh One Side of 24 volt Transformer
W = White Heat

Jan 06, 2010 | Heating & Cooling

1 Answer

Trying to figure out thermostat wiring diagham on a split system


Typical Thermostat Wiring for 4 or 5 wire Heat/Cool Thermostat (not heat pumps)
4 Wire Termostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
with one transformer for both units
Rc One Side of 24 volt Transformer
Rh Jumper Rc to Rh
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
With 2 transformers one for indoor unit
And one for outdoor unit
Rc = Red One Side of (outside) 24 volt (outside transformer)
G = Green Blower (outside transformer)
Y = Yellow Cool (outside transformer)
Rh = Blue One side of (inside) 24 volt (inside transformer)
W = White Heat (inside transformer)
COOLING ONLY Thermostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
HEATING ONLY
R or Rh One Side of 24 volt Transformer
W = White Heat

Jan 05, 2010 | Heating & Cooling

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