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Hi,
I have a Bosch KGU3201GB/05. For several years the defrost cycle has not been worked correctly. After around 6 months the cooling capacity of the freezer is almost nil and upon inspection the evaporator is completed frosted up – blocking air flow.
The unit has two defrost heaters one 300 ohms, the other 2k7 if I recall so no problems there. The defrost thermal cut out looks good too. It is as if the defrost just doesn’t run frequently enough.
So my questions are as follows:
– If the defrost didn’t work at all, would it last several months before blocking with ice, i.e. is the defrost knackered?
– How can I get the service manual? I have reprogrammed it to use timed defrost instead of door cycles and I will see how it gets on but I would really love to have the service manual so I know what the menu options really mean. I.e., can I manually trigger a defrost test program?Other than that, the unit is sound and would be a pity to scrap it but having to defrost for 24 hours every 4-6 months is a pain in the …
Thanks in advance,
Chris Paul
Re: Bosch KGU3201GB/05 Defrost problems …
fwiw, I have had exactly the same problem with my KGU3201GB/07 which I bought in 1998. For the last few years, I manually defrost the evaporator every autumn. But since last Easter, I’ve had to defrost it twice.
I normally use a hair dryer to defrost the evaporator, taking care not to allow any water from the thawing evaporator to drip into the hair dryer. I can normally get my Bosch back up and running within an hour.
I checked the defrost heater elements and the resistances were similar to what you quoted. When I rechecked the evaporator this morning after defrosting it last week, there seems to be evidence that defrost cycles had taken place from the very small amount of frozen ice collected in the drain tray.
After reading your post, I too have now reprogrammed the Bosch to use Timed Defrost mode. Whether it will solve the problem remains to be seen.
It’s a shame Bosch no longer make a fridge freezer with similar freezer storage capacity as the old Logix KGU3201.
Re: Bosch KGU3201GB/05 Defrost problems …
looks like you need a new ntc (sensor),sits in the top of the freezer evaporator to control defrost.
Re: Bosch KGU3201GB/05 Defrost problems …
spimps wrote:looks like you need a new ntc (sensor),sits in the top of the freezer evaporator to control defrost.
There appears to be a thermal fuse, and a NTC sensor.
http://www.bosch-eshop.com/eshop/bosch/gb/prodp.htm?prod=KGU3201GB/07The thermal fuse wiring seems to enter the top of the evaporator through the fins is okay and not open circuit.
Following your post, I quickly checked what looks like to be the NTC sensor enters through a small hole in the bottom right front face of the evaporator aluminium shield. I managed to unplug the cable and measured the resistance at 40k (It was 15-20k when plugged in). The resistance was dropping very slowly the longer I continued to measure the resistance as I guess the temperature in the compartment was rising. I can only deduce the NTC sensor appears to be functioning unless it has drifted out of spec.
I guess if the NTC sensor was faulty, wouldn’t this model flag up a fault code on its 7 segment temperature display?The KGU3201 provides 7 segment readouts of the actual fridge and freezer compartment temperatures. Does anyone know whether there are seperate sensors, or do they rely on the evaporator NTC sensors as there are only two NTC sensors listed in the Bosch parts list in the URL quoted above.
Re: Bosch KGU3201GB/05 Defrost problems …
Contrary to my previous posting, I thought the NTC sensor enters a small hole in the aluminium shield. It looks more likely the sensor is just attached to the outside of the shield.
At the moment, everything is working okay and defrosting seems to be functioning during the past week. But if the evaporator ices up again in the next few months, then I will try replacing the NTC sensor as suggested.
I suspect the same sensor feeds the freezer temperature 7 segment digital readout. When displaying -18C and the compressor is running, a mercury thermometer records about -22C in the lowest bin, and about -15C in the upper most bin when I checked a few moments ago.
Re: Bosch KGU3201GB/05 Defrost problems …
Can someone tell me what is the function of this Bosch part attached to the evaporator used in KGU3201 ?
Bosch 164234 Limiter-temperature (substitute 617855)
617855 is described as a ‘Thermal Fuse’ when I google.
After studying the guides in this forum, is it a ‘Defrost thermostat’ by another name, or is it just a safety fuse?
Re: Bosch KGU3201GB/05 Defrost problems …
NTC is usually the normal running sensor, detects the current temp, reports it to the controller.
Temperature limiter is there to stop the machine from overheating on a defrost cycle usually.
Thermal fuse can be the same thing but some are on-shot devices, they do not reset in a few cases, that’s rare though.
Defrost thermostat is usually the one (normally a good old fashioned proper stat) attached to the evaporator to tell the machine when it needs to defrost. But these are often combined with a limiter or fuse so you end up with one little box of tricks having two or three functions.
Depends on the setup what’s used and how.
It’s all good fun trying to work it out.
The temperature in the unit will be an average.
K.
Re: Bosch KGU3201GB/05 Defrost problems …
kwatt wrote:Temperature limiter is there to stop the machine from overheating on a defrost cycle usually.
Thermal fuse can be the same thing but some are on-shot devices, they do not reset in a few cases, that’s rare though.
K.
Many thanks for the detailed explanation.
If the evaporator becomes choked with ice again, I will definitely check the temperature limiter to see if it is perhaps ‘stuck’ in an open circuit state, thus preventing the defrost heaters from ever switching on.
Re: Bosch KGU3201GB/05 Defrost problems …
Just a minor update.
We had a mini heatwave yesterday. +29C here.
I had a plug-in energy monitor hooked up to the Bosch and by chance managed to catch the Bosch doing an auto defrost cycle late afternoon. While the compressor was silent, the Bosch was drawing around 206 watts for ‘I think’ 20 minutes, and subsequently 27 watts for a further 9 minutes.
The compressor kicked in afterwards but was running for well over 3hr 40min before I forced it off in the evening – I’ve put this down to the heatwave for the time being. (This morning, the compressor ran for less than 1.5 hrs before switching off)
In the meantime, I’ve ordered a new evaporator NTC sensor in case it is playing up and affecting the defrost cycle as previously suggested by ‘spimps’.
I’ve since discovered there is a 2nd NTC sensor elsewhere in the freezer compartment that I believe is used to display the digital numerical temperature readout and I guess provide overall temperature control.Re: Bosch KGU3201GB/07 Evaporator sensor
New NTC sensor arrived but I’m not sure how to fit it. ❓
Required bosch part no. is 164172 but a substitute 602671 is supplied.
Unless I’m mistaken, it does look like the existing sensor on the end of the length of cable is mounted at right-angles, and appears to be pushed through a small hole in the front of the evaporator aluminium shield. (I’ve not yet tried to remove the old sensor)
If the new sensor did have to be pushed into the hole, I think I would be putting unnecessary strain on the cable trying to bend the cable round 90 degrees, and I’m not even sure if the false back panel will fit properly afterwards.
Waiting for Bosch to phone me back.
Re: Bosch KGU3201GB/07 Evaporator sensor
:boops:
After the Bosch had completed a defrost cycle, I took the opportunity to examine the evaporator since I last checked it 2 weeks ago.
After carefully looking at the existing 164172 sensor (see attached pic), I managed to pull it out of the D shaped hole in the evaporator shield. It transpires the sensor and cable were originally straight but there was a tight 90 degree bend in the heat shrink sleeving.
I did observe the old sensor was slightly larger in diameter than the new sensor and it had a D shape cross section designed to fit tightly in the hole. When I inserted the new sensor, it is just a very ‘loose’ fit.
I also looked at the evaporator and it looked very much like it had been totally thawed out during the last defrost cycle.
It is too early to tell whether using ‘Timed Defrost’ CF mode really makes a difference.
http://www.ukwhitegoods.co.uk/forumsphpbb3/viewtopic.php?f=35&t=4666I’ve decided in the mean time to continue to use the old sensor and will keep the new one as a spare.
Other information that may be useful to other KGU3201 owners:
There are four plugs in top left of the freezer compartment. Unless I am mistaken, from left to right:
White plug – Thermal fuse. There should be continuity when tested.
Grey plug – Defrost heater element for drain/drip tray. Measures about 2,700 ohms. (est. 25 watt heater) Appears to run for a further 10 minutes after main defrost heater is switched off.
Black plug – Defrost heater element for evaporator unit. Measures 300 ohms. (est 175 watt heater) I have not been able to determine how long this runs as it does not always start immediately when the compressor turns off – may be controlled by the NTC sensor – minimum of 16 mins to I think 20 mins run time observed to date.
Red plug – fan.
Hope all this info is useful to others.
Re: Bosch KGU3201GB/07 Defrost mode
fyi, I’ve observed the following since changing my Bosch to use Timed Defrost (P11, CF) mode several weeks ago:
1. The freezer compartment’s magnetic door sensor appears to be ignored.
2. Audible alarms appear to be disabled.
Previously when the freezer door is opened, the door open alarm sounds after 30 seconds. Now, it doesn’t sound at all when the door is left open for over a minute.Previously if the fan is spinning, it usually spins down when the freezer door is open. It now continues to spin.
When I’ve inspected the evaporator or when electrical power was restored after a recent 6 hour power cut, the temperature alarm would usually sound immediately when the power comes on. It’s been silent.
(Today, I briefly changed the P11 mode back to CI, and observed the fan spun down as soon is the door opened, and the audible alarm sounded after 30 seconds)
The following are some approximate temperature/resistance measurements I have also taken from the new evaporator NTC sensor:At room temperature, 21-22C, 5k to 6k ohms.
In glass of water containing ice, 6-7C, 11k-12k.
When removed from top freezer drawer when compressor is On, estimated -18C or lower, 49k and falls rapidly.
Re: Bosch KGU3201GB/05 Defrost problems …
Just an update from when I last posted almost 18 months ago.
I can confirm reprogramming the Bosch to use Timed Defrost (P11, CF) mode seems to have solved the issues we have witnessed in previous years where the evaporator would be clogged with ice usually after each summer.
Also, contrary to my previous post, the high temperature warning alarm does sound if the temperature rises above -15C, usually after putting a large quantity of food into the freezer compartment.
I’ve not had to replace the original NTC sensor.
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