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System fan does not come on.

I have an indoor GMC system and a Tapan T3BA-036KA heat pump. My compressor would run without the fan coming on. If I turned the system off and then back on the system would reset and cool with the fan running. I replaced the thermostat with a honeywell RTH7500 series.
Now the fan will not come on even when it (the fan) is set to run continous. I had yellow, green, red and orange wires that I connected to Y, G, R, and O respectly. I also had a W2, E and C that I connected to their matching symbols.

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If the out door unit has been working carefully jump red to green the fan should come on if not problem is bad fan motor or capicitor or fan relay hope this helps

Posted on May 24, 2009

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1 Answer

Icing up outside. no heat inside


Isolate unit to defrost out door unit,
Once defrosted run unit ensuring heat from unit inside and fans are running outside,
if fans and compressor are running and there is next to no heat inside coming from indoor unit this is a common sign of a refrigerant shortage in system and this may cause outdoor unit to freeze up

Jan 24, 2016 | Mitsubishi Electric Mr Slim E12C26426...

Tip

Why your unit is freezing up.


To understand why your AC or heat pump is freezing up, it helps to know how your system works.

There are 7 major parts to an AC system, 9 with a heat pump.

1 - Condenser/heat pump (The outdoor unit)
2 - Air Handler (the indoor unit unless the system is a package unit, then all is outside in one system. The air handler is usually found under the home, in an attic, or in a closet.)

In the condenser are the following major parts.

3 - Compressor
4 - Condenser coil
5 - Condenser fan
6 - (HPs only) reversing valve

In the air handler are the following major parts.

7 - Blower motor
8 - Evaporator coil
9 - (HPs only) electric heat strips

Some systems known as "dual fuel systems" use another heat source in place of the heat strips, usually a gas furnace. I will address gas furnaces in another post.

When an air conditioner is operating properly several things are taking place.

1 - The compressor is compressing or "pumping" refrigerant through the system.

2 - through changes in pressure, the refrigerant makes the evaporator coil get very cold, and the condenser coil gets very hot.

3 - The blower motor/fan circulates air across the evaporator coils, as the room temperature air (Also known as "indoor ambient") goes through the cold coil, it exits, cooled approximately 15 to 20 degrees cooler than when it entered. (In a ducted system, the blower is also the fan that circulates the air throughout the home.)

4 - The condenser fan circulates air across the condenser coils. As the outdoor air goes through the condenser coil, it removes heat from the coils that are very hot. This in turn removes heat from the refrigerant so it can run its cycle again, and through pressure changes, cool the evap coil.

5 - With a heat pump, the reversing valve reverses the flow of refrigerant in the condenser and evaporator coils.
In AC mode, the evaporator coils get cold, and the condenser coils get hot. But in heat mode, the evaporator gets very hot, and the condenser very cold.

Now, whichever coil is getting cold will freeze up if there is inadequate air flow across the coil, as the refrigerant in it is far below freezing, and there is not enough airflow to keep the humidity in the air from freezing on the coil.

Things that can cause poor airflow are,

1 - Dirty/clogged coils
2 - dirty/clogged filter (will only effect evaporator coil)
3 - Closed/blocked vents (will only effect evaporator coil)
4 - Malfunctioning or dirty fan

Low refrigerant will also cause a coil to freeze up, reduce efficiency and cause the system to run for long periods of time. Not to mention, shortening the life of the unit.

With a heat pump, in heat mode only, the condenser (outdoor) coil will routinely begin to freeze up in cold temperatures. This is due to the fact that the refrigerant is below freezing, and the cold outdoor ambient temp is not warm enough to keep the condensation in the air from freezing on the coil.

Note, a properly working AC should never freeze up.

A heat pump is equipped with defrost controls to prevent ice buildup.
Some are controlled by timers, some by temp.

When a HP is going into defrost mode, the condenser fan shuts down, the reversing valve reverses the flow of refrigerant and the once cold condenser coil now gets very hot, defrosting the coil. (Many people have said this process sounds like the unit is coming apart, or about to explode and are frightened by the "smoke" which is really just steam from melting ice that comes off the unit.)

During defrost mode, the secondary or "auxiliary" heat comes on to ensure that you are still getting warm air from the vents. (Again, this can be electric heat strips or a dual fuel system)

If you are experiencing cold air from the vents during defrost, that means your auxiliary heat is malfunctioning.

The auxiliary heat is used for three purposes.

1 - during defrost mode to maintain warm airflow (automatic)
2 - when the HP cannot maintain the set temp due to extreme outdoor temps. It comes on when the indoor temp drops several degrees below the set temp on the thermostat (automatic)
3 - For emergency heat source when the HP is not working. (Manual)

To recap....

Iced up coils?

Poor airflow
low refrigerant
Malfunctioning fan
failing defrost system


There are two things that can be done in a pinch to help de-ice frozen coils. This may get you by until the repairman can get there, or you can fix the system if you are a do-it-yourselfer.

HPs frozen outdoor coil in heat mode, not going into defrost?

Cover most of the vents, and turn the system onto cooling mode until the outdoor coil is thawed. then uncover vents and return to heat, or emergency heat. (this usually takes 15 min or less)

Frozen coils in AC mode with a heat pump?
Turn the system to heat with the thermostat on just high enough to get the system to come on. (again, usually takes 15 min or less to thaw.)

AC only, with frozen evap coils? (this can sometimes be seen frozen all the way outside to the compressor on the copper lines.)

Turn the system off, and the fan switch from "auto" to on".
This will usually defrost the coils within 1 to 2 hours.
(If your system has the furnace in line before the evap coil, turn the system to heat, and the furnace will defrost the coil within minutes.)



on Dec 25, 2008 | Carrier XHB123D X/Y Series Heat/Cool Air...

1 Answer

Coolant fan doesn't come on unless I run air conditioner.


"Coolant Fan" is not necessarily a common term used to refer to any particular fan in a standard HVAC system. Are you referring to the "Indoor Fan" that circulates the air within the living space???? OR are you referring to the "Outdoor Fan" or "Condensor Fan" that circulates the air across the outdoor coil ??

If its the indoor fan on an air handler that's not running unless its in A/C mode, it will be a faulty heating circuit fan relay on the main control board.

If its the outdoor fan and its a heat pump system the outdoor fan stops during the defrost mode so there is a slight possibility the system defrost board is faulty and stuck in defrost.

A little more information may help obtain a more specific answer.

Apr 14, 2015 | Heating & Cooling

1 Answer

Friedrich ductless heat pump will not start up.


Did you check to see if the compressor is running? Check out start relay/capacitor.

Sep 21, 2017 | Heating & Cooling

1 Answer

Fan doesnt work on heat cool ok


Often the fan will cycle on and off on the heat mode. A cold air prevention mode is often built into modern Ac units whereby the indoor fan wont turn on until the internal system pressure is up to a certain point and heat is available to pump into the room. If the system cant come up to pressure or temperature then possibly the system is low on gas. Place your hand on the large pipe leaving the outdoor unit, it should be HOT when the system is on heating mode and running. If not Hot, then it is low on gas.

Feb 24, 2011 | Pace 18HPEWHEC Split System Air...

2 Answers

I have a T3BA-036KA the outside unit will not


You need 24 volts going to the coil of the contactor. If you do not have 24 volts, you will need to trace the wiring back to see where you are losing it from. Try placing your voltmeter at C & Y coming from your air handler. If not, go to your air handler and test for 24 volts ac at C & Y coming from your thermostat. If you do not have 24 volts coming from your thermostat, there is either a problem with the thermostat or there is a problem with the wiring between the thermostat and the air handler. If you have 24 volts at the air handler coming from the thermostat but you do not have 24 volts at the outdoor unit coming from the air handler, then you have a problem with the wires between the air handler and the outdoor unit.

I hope you find this information to be very helpful to you moving forward. Please leave a rating. :-)

May 10, 2010 | Intertherm P3RA-036K Air Conditioner

1 Answer

Is a split a/c alc and a heating or heat pump?


a split system can be gas or can be a heatpump. a split system is when the condenser coil compressor and outdoor fan is outside. the other half is in the house close to your air filter .that well be your air handler. eletric heater. or gas burner .and indoor fan motor would be. i hope that helps you.

Apr 15, 2010 | Cfm Daikin R410a Split System Air...

1 Answer

The ac comes on but the fan is not turning or comes on


Hi, I assume this is a split system, with the indoor and outdoor unit. If you are talking about the fan on the outdoor unit, this is the condenser fan motor. It is exposed to the heat of the ambient temp. and removing the heat from indoors. If you have a heat pump, this motor runs year around and gets a lot of use. I have seen the 5mfd run capacitor fail which could cause this motor not to start, but more than likely the condenser fan motor has burned out.If it is the outdoor unit you are talking about, can you hear the compressor come on when you start it? You may stand by the unit and have someone turn the t-stat to cool and see if you hear it come on. It will shut off after awhile due to high head pressure. But, if nothing happens, you may not be getting power from the breaker being tripped or a blown fuse at the disconnect box at the unit.Check these before calling out a tech.If you are talking about the indoor fan, make sure the panels are on good if its a gas unit as there is a door switch that is closed and if the panel is loose, it will stop the fan from coming on. The indoor blower motor may also be burned out. It shouldn't take more then an hour at the most to find out what is causing this problem. Could be a fan relay. I would recommend calling a qualified a/c Co. to come out and check this. Wish I was there and could be of more help.
Good Luck, Sincerely, Shastalaker7

Oct 31, 2009 | Goodman CLQ36AR49 Air Conditioner

1 Answer

Honeywell Thermostat


Make sure G from indoor unit goes to G on thermostat for fan continous fan, if that doesn't work and you have 24 volts to R and C then the t'stat is bad.
For 2nd stage heat or aux.heat, on the indoor unit you need to make sure the wire W2 from the indoor unit goes to W2 on t'stat.
You don't need any wires from W1on the indoor unit to W1 at the t'stat because with a York heat pump Y1 is the contactor which turns the compressor on and you will get 1st stage heat, and for cooling the t'stat will also bring on O which is the (reversing valve) or cooling changeover relay for the cooling mode.
C = common usually black wire
R = hot usually red wire
Y or Y1 = contactor
W1 = 1st stage heat not needed for heat pump
W2 = Aux. heat indoor heat
G = fan
O = Cooling changeover relay
B = Heating changeover relay
L = System monitor
E = Emergency heat relay

Dec 23, 2008 | Honeywell Electronic Programmable...

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