Strange CCU Issue...Opinions?
#16
Three Wheelin'
#17
Rennlist Member
AC wasn't working for years but fans blew heat and outside air until a few months ago when it seemed to work when fan speed was at highest setting. I did not think anything of it and decide to finally convert from R12 to R134. Took it in and everything was done and mechanic told me as they were testing that it blew a fuse (1), they replaced the fuse and everything was fine for a few days. Now it stopped working altogether. Fuse 1 looks fine so it must be something else. I need to check the other fuses Tore suggests too. So what was your result?
#19
Rennlist Member
Faults in the CCU power switching mechanism is a known problem. If the unit does not shut off as expected an internal transistor needs to be changed. Details here.
Cheers,
Tore
Cheers,
Tore
#21
Rennlist Member
Loren, a good rule of thumb in web forums is to refrain from posting if it does not contribute to the topic.
Even better, write something that helps solving the problem.
T
Even better, write something that helps solving the problem.
T
#22
when the ignition switch is cycled to the off position. There are situations where that transistor is OK and the CCU still fails to turn-off when
installed in the vehicle, requiring the CCU to be repaired other than by a simple transistor replacement. This has been the case when repairing
CCUs for 15+ years.
Read here; http://www.systemsc.com/problems.htm , under CCU 964/993
Last edited by Lorenfb; 04-10-2019 at 12:39 PM.
#23
Technical Guru
Rennlist Member
Rennlist Member
Are there any further steps that we can use to troubleshoot this prior to the owner pulling the transistor and testing it themselves or sending the CCU out for component replacement?
#24
Rennlist Member
If the unit does not shut off within 20 minutes, I would start with changing the BC337 CCU power relay transistor.
This is part of my standard refurbish/repair procedure on these units.
Cheers,
Tore
This is part of my standard refurbish/repair procedure on these units.
Cheers,
Tore
#26
These measurements are taken from the back of the CCU with both CCU connectors plugged in.
Tests with the CCU removed are simple. Check that pins K1 and G18 (grounds) are connected internally. Using a 12V power supply, first connect
G18 to the -12V lead and then connect K2 to the +12V lead. Next momentarily connect +12V to G35 to power the CCU on. Then wait
about 10 seconds and the CCU will turn off. This will verify that the transistor controlling the power relay functions properly. If you need to
actually check the transistor in the CCU, just use the diode function of VOM to measure the two PN junctions (BE/BC) & the CE resistance
of the transistor.
Last edited by Lorenfb; 04-11-2019 at 12:56 PM.
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JasonAndreas (12-07-2020)
#27
Instructor
I see a couple slightly different appearing pin arrangements for the BC 337, from online pictures its not possible to determine if the pitch of the pins is actually different of it just looks different because of the size of the transistor portion.
Is there a supplier than is know to have a pin arrangement that slides right in?
What is the next item to look at if it's not the BC 337?
Thanks
Is there a supplier than is know to have a pin arrangement that slides right in?
What is the next item to look at if it's not the BC 337?
Thanks
#28
Rennlist Member
You just bend the pins. Any type will do.
Cheers,
Tore
Cheers,
Tore
#29
Instructor
So after the CCU fan being on continuously for a week I went to the garage to get something out of it and now the fan is off. Weird. Does that potentially indicate some other problem?