How a Condenser Tumble Dryer Works

 First and Foremost Electric Shock

Attention!  Electric Shock Can Kill!  Before you do anything else. Before you remove the cover of any electrical appliance. This includes your condenser tumble dryer.  If it is your intention to carry out work. Make certain that the power is off! Remove the plug from the electricity supply socket before proceeding with any work or investigation! Because once the plug is out and the plug is within your sight and reach. You know that you are safe. Even if someone accidentally switches the power on again.

Condenser Tumble Dryer Air Flow

There are two air circulation paths operating in parallel inside a condenser tumble dryer. The cool air circuit, blown by a fan such as this typical plastic molded fan continuously blows cool air. The dryer draws cold air in through a vent in the casing of the dryer. The cold air is then blown through the veins of the condenser unit to maintain the temperature as cool as possible.

Typical Siemens Condenser Dryer
Typical Siemens Condenser Tumble Dryer Exclusive to Euronics and Agent stores, this Siemens extraKlasse dryer boasts a 9 kg capacity and a choice of 15 programs

Environment Location

Condenser tumble dryers should be located in a low ambient temperature environment. As low as can reasonably be achieved. This way the dryer is able to work more efficiently. If the dryer is working in a centrally heated room where the room ambient temperature is a comfortable 60’F, (15’C), drying will take far longer.

Condenser Tumble Dryer Other Airflow

The second airflow system is at the same time blowing hot air. Heated by the element inside the dryer, the hot air passes through the center of the tumbling clothes. Here the hot air picks up moisture from the clothes. It continues via the lint filter and ducting inside the machine, to the condenser unit. The warm air however blows through the veins at right angles to and interleaved with the cool airflow.

The warm moisture-laden air flows through the condenser simultaneously to the cooling air. So it is thereby, encouraged to give up its moisture, (condensate). Gravity drains the condensed water into the reservoir tank. The water can then be drained out manually, pumped out to an external drain or into a waist-high reservoir tank.

White Knight condenser dryer pumpCondenser Tumble Dryer Reservoir Bottle

Every condenser tumble dryer needs a reservoir water bottle. The bottle requires emptying frequently. Situated near to the floor, this saves on the cost of a pump. Generally, this is less complicated, less to go wrong. Other condenser tumble dryers locate this bottle near the top of the dryer. These dryers need to have the water pumped into the reservoir bottle or straight out to an external drain.

Condenser Tumble Dryer Circulation Fan

In some condenser dryers, see the Which guide to buying a condenser dryer, the two fans are positioned on the shaft of the one motor. One fan situated at one end of the motor shaft. The other fan on the opposite end of the motor shaft. The synchronous motor will run at only one fixed speed. So the speed of the fans is pre-set by the required drum rotation speed and the diameters of the drum and the motor pulley. Indirectly the required drum rotation speed determines the speed of all three functions as there is only one motor.

In some condenser tumble dryers, they choose to have a separate motor with its own fan. Supplying the cold air for the condenser cooling circuit. This has the advantage of being able to independently determine the speed of the cold air fan motor. This unit is free to locate anywhere appropriate in the dryer. Because a separate motorized fan improves the overall efficiency of a condenser tumble dryer.

Quick Maintenance Procedures

First of all, after every use, you should check the lint (fluff) filter. In every tumble dryer, there is a serviceable, washable, replaceable lint filter. The filter requires cleaning after every drying cycle and replaced as and when necessary.

Typical tumble dryer lint filter

Second, on all condenser tumble dryers, there is the condenser itself. The condenser is located where it can very easily be removed so as to facilitate cleaning. Carry out cleaning by running water through the condenser. An alternate method is to immerse the condenser into a bowl of water so as to agitate the condenser around in the water. This will then remove as much of the build-up of sludge and lint as is possible. DO NOT SCRAPE OR CLEAN WITH A KNIFE OR ANY ABRASIVE TOOL. Because the veins in a tumble dryer condenser unit are made from extremely thin stainless steel and so are very easily damaged.




Carbon brushes Bosch type 154740 Fitting Information


Personal safety at all times

First of all, if you are going to examine the Bosch 154740 carbon brushes, this is of utmost importance! Disconnect the appliance from the mains electricity supply! Do this by removing the plug from the supply socket or by switching off at the main consumer unit.

This can usually be accomplished by switching a single breaker, which, if it is an up to date RCD (residual current device) hopefully it will have been labeled Kitchen Sockets, Utility Room Sockets, House Sockets, Garage Sockets, you get the idea. Where ever your appliance is situated. It may also be a wise move to ask anyone who is working at a computer that is mains powered to back up their work before switching off.

Checking the motor carbon brushes

Down to the actual brush changing! All Bosch washing machines that use these Bosch 154747 carbon brushes are not the same,  nor do they even use the same Bosch motor.  In fact the only thing that they have in common is that they all use these carbon brushes part number 154740.

Bosch 154747 Carbon Brushes
Bosch 154740 carbon brushes are the most common motor carbon brushes used in Bosch washing machines.

First of all, remove the rear panel from the machine, on some models this will be enough for you to be able to remove the single fixing bolt, slacken the tensioner bolt and remove the motor. Carefully disconnecting the plug on the motor from the socket on the machine. On other models you will need more access than described above to actually access the motor fixing bolts. The best way to do this is to lay the machine down on its side with the soap dispenser to the top away from the floor, this will give full access to the motor fixing bolts.

Having removed the motor, examine it for any physical signs of damage, particularly the surface of the commutator where the brushes touch and rub on and actually make contact with the armature. When the surface of the commutator appears to be damaged because of the worn out carbon brushes, you are looking to see if any segments of copper are raised and out of line with the rest. If this is the case it is absolutely final and requires a replacement motor!

Testing the motor

To test this requires the use of a megger or some other voltage producing tester, but a simple test can be carried out with a basic resistance measuring meter, such as a multimeter which may be purchased at a very reasonable price.  

Before doing a test, switch on the meter and set it to the lowest Ohms range. Touch the two test probes together and the screen should indicate zero resistance. This check ensures that the meter is actually working and does not have a flat battery or some other fault. Next, touch one probe on to the frame of the motor and the other probe on to the surface of the commutator. Should you see any reading at all there is a problem and this needs either testing with the proper equipment or the motor needs to be replaced as there should be no electrical connection at all between the commutator (live) and the frame of the motor (earth).

No Reading is Good

If you do not see a reading on the meter screen, good, but this is not necessarily the end as this is only a crude test and is an indicator only that it may be worthwhile continuing with fitting the replacement carbon brushes. Another quick test you can carry out with a test meter is, touch one probe on to one of the brass brush holders and the other probe on to each connector in turn in the motor socket until you see the meter read zero ohms once more, then repeat this from the other brush holder, this is telling you that the temperature fuse embedded in the motor windings is OK and has not blown due to the motor overheating.

Having come this far, remove the Bosch 154740 carbon brushes retaining tags from the end of each brush holder. Withdraw the worn out carbon brushes which may be intact but may also have broken up and disintegrated. Once removed, it is good practice to clean off all of the excess carbon dust from anywhere on the motor. Do this using a dry cloth or paint brush or an airline if you have access to one.

Fitting the replacement carbon brushes

Having done all of this, you are now ready to fit the replacement Bosch 154740 carbon brushes. Gently slide the new carbon brushes into their respective brush holders. Do they slide in all the way freely without jamming?  If so, fine, replace both carbon  brushes the same way. If the brushes do not slide freely all the way in, do not use force. Instead withdraw the brush or brushes before they get jammed completely. What has happened here is that the metal brush holders have distorted, maybe only very slightly. This is due to the continuous heating and cooling of the motor throughout its working life.

What you need to do now is to use a file or a Stanley knife or some other scraper. Gently scrape away at each corner of each carbon brush. Do this to each corner in turn until the carbon brush slides into the holder freely. If this does not work try scraping one edge of the brush. Do this just until it slides freely into the holder. Both carbon brushes must be free to slide in and out of their respective holders before carrying on any further.

Having accomplished this, push the spring down the brush holder and replace the tag to hold it in place. Repeat this for the second brush. Now, rotate the motor shaft with your hand and ensure that it is not scratching and clicking as it rotates.

Cleaning the commutator

Correct any excessive clicking of the new brushes by cleaning up the commutator. Do this using a comm stick. Do not use emery cloth or sand paper as these can cause serious damage to the motor. Take the motor to a reputable trades person should you not have access to a comm stick.

When you have done all of this, then it is time to replace the motor into the machine. Use the reverse procedure to the removal. Once the motor is back in its location in the machine, tighten the securing bolts. Apply gentle tension to the drum drive belt. Do not over tension the belt! After replacing the machine covers, you should now be ready to test the machine. Now to find out if your repair has been successful!.

Hope this helps, and good luck with your repair project!