Advantages of the short nosed bonnet?

prm · Post by **prm** » Thu May 21, 2009 7:12 pm

Have a look at,

http://partfinder.smpeurope.com/index.html?p=1

All 50101 switches show M22x 1.5 threads, 29mm spanner size, with a 3 pole connection.
A good cross reference and vehicle application sections.

While your replacing the temp switch would certainly recommend fitting a 82° stat.

Over the years fitted various combinations of stats and temp switches and found this combinations works really well, with very little fan operation while mobile.

After monitoring the operating temps on various sections of the cooling system with this set-up, the temp gauge should rise quite rapidly to approx 85-86°, then normally oscillate between 85 and 92, just before the slow speed fan kicks in.

I’ve wired up a relay into the high speed terminal of the temp switch, connected to a surplus dash warning light recess, to indicate when the fans are on high speed, or, the light of death!!

Regards

Post by **mat_fenwick** » Wed May 27, 2009 10:26 pm

Interesting idea about the high speed fan operating a warning light. I've only had it operate on high speed twice, and that was down to the A/C rather than engine temperature.
I do have a question on the usual failure mode of the temperature switches - at the moment if my gauge rises much above half way, the fan doesn't operate (as it would normally do) but there is a relay chattering in the relay box under the scuttle panel. From memory, on no A/C cars the temp switch operates the fans directly(?), but on A/C cars, it does so via relays so the A/C can also switch in the fans.
My theory is (haven't had chance to check yet) that the contacts in the temp switch now have a high resistance, so there is insufficient voltage at the relay to hold it closed, Does that sound feasible? Or do they normally fail in one position?

Jaba · Post by **Jaba** » Thu May 28, 2009 12:11 am

No idea how the rad thermo switch fails but there is something not right about what you describe as no relays are energised at the moment when fan low speed is called for with or without a/c if the car is wired up as standard.

Also there is only one relay in the low speed rad fan circuit, 774, inside the car and this is on all the time with the ignition and is used with and without a/c.
Do the 2 fans come on at low speed without the clicking when the a/c is on ? If so this points to rad switch. Easily checked if off the car while heating in water or on the car by shorting the low speed connector to earth.
Those radswitch connections are often suspect as they pass a lot of current and can get corroded. I seal mine on with silicone to keep the muck out.

Post by **mat_fenwick** » Thu May 28, 2009 10:59 pm

Jaba wrote:Do the 2 fans come on at low speed without the clicking when the a/c is on ?

They don't. But I had assumed that was due to the fact that the A/C had stopped working after an 18 month lay up. I had put that down to a small leakage over time, but thinking back to the wiring diagram I'm not sure that a lack of pressure on the receiver drier pressure switch would cause the fans not to run as well as stopping the clutch from energising. Therefore the A/C not working could be linked to the fan/relay problem. The rad switch connections are good, I use silicone grease to keep the water out. When I did the engine swap last year they were still bright and clean.
Time to find that wiring diagram (stuck on another PC with hard drive failure

) and have a ponder... The annoying thing is that everything is backed up, but onto a Zip drive which I can only access from the dead PC. Can't swap the Zip drive as it is a SCSI connection, and I can't swap the SCSI card as it fits into an old ISA slot. Ho hum.

Jaba · Post by **Jaba** » Thu May 28, 2009 11:50 pm

OK - the a/c problem wont affect the fans running from the radswitch as long as neither the fans or compressor run with a/c on.
If the fans come on when you short the radswitch contacts to earth then its probably the switch failing on the low speed contacts.
I have emailed you the aircon wiring for a diesel BX. I am sure this will help you to pinpoint the problem
It is available also on Bob Smith's site still HERE

prm · Post by **prm** » Fri May 29, 2009 2:53 am

Initially the best way to check that you’ve both high and low speed fan/s and circuits operational, is to remove all three connectors on the temp switch, and in turn, bridge each one down to earth/negative. One wire – slow speed, one - high speed and 3rd wire zero - common earth.
Connections should be – with the single non opposing tag (common to earth) at 6 o-clock, vertical left = high speed, vertical right = slow speed.
One word of caution, would strongly advise before bridging to earth. Check voltage to chassis on all three wires with an inline meter/bulb first. I’ve seen systems where the temp switch has been connected with a live direct feed - with ignition on, and fans supply- positive, routed through the switch.

The main failings with the temp switch are age, where the low temp side fails or the temp bands become wayward.. The single fan set-up with the resistor, causes a reduced life span, due the higher amperage this sometimes has to carry with ageing wiring and connectors on slow speed , thus increasing internal bimetallic strip loadings
You may find the copper wiring strands adjacent to the resistor, blackened due to overheating.

The twin fans should operate on high speed with the dash air-con switched on, irrespective of water temp and refrigerant charge pressure. As the main air-con relay bypasses the temp switch when activated.
If the system is low on pressure, below approx 3 bar, the dryer pressure switch fails to engage the compressor clutch relay. Likewise, if the pressure exceeds 19bar.

A drawing plus a few mods that may help with the fan/temp switch set-up.

http://i295.photobucket.com/albums/mm15 ... ods1_1.jpg

I will try and finish the second drawing that includes the air-con section. When I can finally get the parts out of the boxes and fit them.

There’s one or two mods to include over the original spec drawings.
Tom Shep. ( Mr.Air-Con) mentioned one particular section that possibly needs to be protected. The main temp control module (60). Which, I should imagine???? Is no longer available, or, it would be valued at £2000.

Regards

Post by **mat_fenwick** » Fri May 29, 2009 11:17 pm

Thanks for the replies, my memory is refreshed! The diagram reflects how I wired the A/C, so as the fans do not cut in when it is turned on, it appears as through there is no output from the control unit (60). I will check the thermal switch, hopefully this weekend and hopefully make some progress.
I plan to put in a new radiator (from Ken Newbold) this summer so it would probably make sense to replace the switch anyway, for piece of mind. Ironically I have several spare, but all operating at higher temperatures.

Post by **mat_fenwick** » Tue Jun 02, 2009 5:34 pm

Still not checked out the thermal switch (most of my weekend was spent welding - nice weather for it!) but good new is today that I ran a temporary 12V feed to the A/C set up replacing the trigger from the control unit. Fans cut in slow, as normal, and icy cold air!

So I don't have a leak...I had worried about the RS24 (R12 replacement) being more prone to escaping, but it all seems good.

prm · Post by **prm** » Tue Jun 02, 2009 8:25 pm

Well done Mat. You may need it this summer. A BX with air-con. You lucky bugger!!!!

Your halfway there with your direct feed.
It could be the relay on the main control module (60) that’s playing up and needs protecting long term, from high amp throughput.

A mod that may possibly get your AC fully operational.

If you locate the compressor/dryer/clutch relay main feed wire at terminal 7B5 on the module (?? the blocks can vary) multipin plug.
Cut and connect this wire from the module to the coil side ( ter1) of a BX type 25-30 amp relay, with a suitable earth on relay coil, terminal 2.

Splice into the input supply adjacent to the module, @ 7B7. Connect to T3 on the relay. Then send relay T5, to connect to the cut wire from pin 7B5.
This mod should protect and transfer the internal relay on the module to an independent easy replaceable relay unit.

Hope this may help.

Regards

Jaba · Post by **Jaba** » Tue Jun 02, 2009 10:38 pm

Pete, that was a really impressive diagram of your wiring mods, very artistic too.

However Mat's problem is that the output of the c/u 60 is zero volts. This is not a good situation, that control unit is like gold dust. Wiring in a permanent 12v to the aircon will result in the compressor being on permanently. The evaporator will eventually freeze up.
Mat if it helps, the resistance of the evaporator temperature sensor, 620, should be (from memory)5 -12kohm, the resistance rises with temperature drop.

When and if you can prove that the c/u has failed I may be able to help out with the loan of a c/u.

There is an urban myth that R134a leaks out at a fast rate compared with R12. Perhaps it does on a theoretical level but I have seen no evidence of it yet on my GTi, R134 converted 3 years ago.
I still have a BX with R12 in which still holds pressure after all these years, which makes me think that a sound leak free system will hold its pressure for a very long time.

prm · Post by **prm** » Tue Jun 02, 2009 11:12 pm

Many thanks Jaba. Down to a miss spent youth, middle age and old age.
Need to design my drawings in colour now, as my black on black!!! eye sight is P--- Poor.

Might be worth checking the dashboard control switches and contacts, as the module needs to see a signal/s from these to actuate.

Will dig out the module and circuit test to see how the circuits are laid out.
Are they still available??

Price.

Mat

If all else fails and the module is found to be at faulty.
If your able to run without it installed. PM me, I will certainly have a look.
Not impossible to modify the module, utilising some of the circuitry.

Regards

Pete

Post by **mat_fenwick** » Tue Jun 02, 2009 11:18 pm

Thanks for the tips guys, at least having put it all in myself I know where all the bits are located! I wasn't planning on running the compressor continuously, but the 12V feed at least proved I still have an operational system. It's been about 3 years since it was charged, but after about a year with no engine in the car I figured I must have developed a leak, happily not.
I'll check the control module, it may be that it isn't getting its feed, or perhaps the slider switch isn't making a decent contact. The relay mod sounds a good one, basically just using the output from the built in relay to close a standard relay if I understand you right.
Thanks for the offer John, hopefully it will be possible to mend the control unit if that has failed as I would imagine the internal relay is a standard PCB mount relay available from the likes of RS or Farnell. The rest of it I would guess is a simple voltage divider circuit with the temperature sensor and slider switch, using an op-amp to switch a transistor to operate the relay...that kind of thing rings vague bells for me from when I was at college!

EDIT - I think we posted at the same time Pete!