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Heating coils will not heat up

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To continue from my last Question, to do with HVAC Evaporator/Condenser Cycles, how often should the System go into Heat Standby, Heat Defrost, and Heat Modes? What are Heat Standby and Heat Defrost?


In this type of system (heat pump), the evap and condenser swap functions by means of a reversing valve, according to the mode selected. Evaps throw off cool air, condensers, warm air. In heat mode, the condenser is the indoor coil and it throws off heat from the outside air. Vice versa for the cooling mode. Heat Standby would be whenever the temperature thermistor has reached set point by the user and shuts down the system. Heat defrost is the cycle that reverses refrigerant flow and defrosts the outdoor coil by sending warm refrigerant liquid to that coil. In heat mode, the outdoor coil builds frost and ice on its surface.

Feb 05, 2015 | Refrigerators

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

I have a beko dcu9330 dryer givin n heat. changed blown sensor and tested both sesors, still no heat, no power getting up to heater. whats next step?


Electric dryers have a heating coil over which air is drawn to heat it up. Unplug your dryer and use a continuity tester to check the heating coil for breaks. Attach one lead to one coil terminal and the other lead to the opposing terminal. No reading indicates a burned out coil (very common). All coils are replaceable.

Oct 22, 2014 | Dryers

1 Answer

When the motor is hot it will not start. after it has cooled (8hours) it will strart and run fine. The ignition module tested OK, the coils tested OK. I?m at a loss on this one.


When the ignition module was tested,they most likely did not run it and then test it,when the ignition module does this,it will check good,until it is heated up,with the run mode setting on the tester,so have them do this when they test it,but,it is most likely the problem,if not,the crankshaft sensor is the next likely problem.If this was helpful,please rate,thank you.

Jul 04, 2010 | 1992 Buick Regal

2 Answers

TUMBLE DRYER NOT HEATING UP


ALWAYS UNPLUG YOUR DRYER BEFORE ATTEMPTING TO DO ANY WORK ON IT.
Check to make sure you are getting full 220 Volt power to the dryer, if you are then:
Sounds like your problem may be with the heating coil. Remove the back of the machine and try to locate the air duct going from the blower to the drum. Normally inside the air duct you will find the heating coil and the thermostats/thermistor. Once you have located the heating coil, remove the two wires from it and check the coil with an ohm meter across the two terminals of the coil. You should read continuity across the terminals, if not you will need to replace the coil as it is faulty. If the heating coil is ok, then: You can check the thermostat/thermistor by removing the two wires and taping them together with electrical tape. If the coil heats up then replace the thermostat/thermistor. DO NOT LEAVE THE WIRES TAPED TOGETHER AFTER THE TEST. This could cause a fire, as you have removed the safety of overheat from the machine. I will include these two websites for parts and further help:

Dec 04, 2009 | Dryers

1 Answer

Dryer starts, heat up than the goes out


Faulty gas valve coils are the typical cause of this type of "cycling". These electrical coils are right above the gas valves and when energized, these solenoids open the gas valves and permit the burner to light. If any gas valve coils are suspected of being faulty, it is recommended that both (all) be replaced at the same time. Hope this helped and best wishes.

Sep 02, 2009 | Dryers

1 Answer

Dryer has no heat.Changed the heating coil rear


Maybe you already know this, but occasionally the coils will swell when you first turn them on and they expand to the point of arc'ing off the housing. This puts you right back to square one. I learned the hard way to buy the entire assembly when changing and not just the coil. Not sure if this is your problem or not, but worth another check. I believe the next step would have to be in the control system.

Aug 30, 2009 | Frigidaire GLEQ2152ES Electric Dryer

1 Answer

Heats up basement


Dehumidifiers and how they work
Heat pump dehumidifiers

Dehumidifiers use a heat pump (similar to an air conditioner's heat pump) or chemical adsorbents to remove moisture from the air without cooling the air.

A heat pump dehumidifier uses a fan to draw indoor air over a heat exchange coil. The coil is almost freezing. The water in the air condenses on the coil and is drained. A second heat exchange coil reheats the air, which the dehumidifier exhausts into the room.

A heat pump dehumidifier dumps heat lost from the compressor and fan motors into the air. It returns to the indoor air the heat generated by the dehumidifier turning water vapour to liquid. I got this off the internet

Jun 24, 2008 | Maytag M7DH45B2A Dehumidifier

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