| Author | Message | |||
     Omar Shams Unregistered guest Posted From: 86.96.228.89 |
I have a 1993 Bentley 8 and a 1991 Silver Spur both of which have the same problem regarding air conditioning. The problem with both of them is that the A/C does not come on for many minutes after start up and sometimes not at all. on other occasions, the A/C will switch off and then come back on a little later. often the symptom is coincidental with the autoride light comming on. The dealer tells me that the "microprocessor" has failed and needs replacing. This is an expensive part. Is there a way to override the inhibit? can the microprocessor be repaired? is this a common fault? many thanks Omar in Dubai (Message approved by david_gore) | |||
| Lawrence Heasman Experienced User Username: lheasman Post Number: 43 Registered: 5-2008 |
Hi Omar, I am experiencing the similar in my 89 Spur. The aircon comes on to start, then the lower air-vents under the dash and seats start giving out rather warm air eventhough the lower thumb wheel is all blue! If I turn the whole system off for a minute or so it comes back on again all OK for the next 30 mins or so before I start getting hot feet again! I have also noticed it struggles to maintain cool air on days that are 30c or above and the air flow will randomly switch from facia to windscreen! How much are these 'mother boards'? | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1681 Registered: 4-2003 |
This is a common problem, but fear not. I assume that you have checked the six relevant Bosch relays underbonnet. There are 8 relays in two rows of four, located next to and behind the mineral oil reservoirs, with some clearly marked Heater Tap, Heater Fan Control and Fan Speed 1, 2, 3, 4. Look at the labels on the relay support frame at the rear. Check that Fan Speeds 1, 2, 3 and 4 all click in at some setting of the temperature dials and climate control modes. If the system works at all, then the Heater Fan Control Relay and Water Tap relay are functioning correctly. If all the relays respond, then most commonly the resistor board has failed. That is the black finned thing about 10cm x 6 cm x 3 cm on the left hand bulkhead to the top near the ridge below the bonnet and to the above left (looking forwards from the driver’s seat). It comes out with just two bolts and an electrical plug. They cost a bomb, but are easily tested for continuity between all pins on a bench. I have repaired three using diodes to drop the voltage for intermediate speeds instead of the resistors which do burn out over time. That is an improvement and a 100% repair. I can provide details. If not all the relays click at some stage, then there is the microprocessor board. If it works at all, it is repairable if faulty. I have repaired a few microprocessor boards. Usually, only one of the Microrelays (1cm x 0.5cm x 0.25cm) on the board has failed. They cost about $4 each. If you are good at electronics soldering, replace them all for good measure. I can give you the Tyco or Fujitsu Microrelay part number as there are two configurations. They are standard industrial items available at any electrical trade wholesaler. Fortunately, to prove it all I have a spare repaired Microprocessor board for my own use and bench system testing. However, there is a patch. It works, and is a reasonable as a permanent solution, and saves attacking the microprocessor board. If you locate the faulty resistor or speed setting, whether due to the microprocessor board or to the the resistor board, you can do the patch. Locate the relay not energising, or the resistor path without continuity, and causing the missing fan speeds, at the relay set on the left hand valence near the dashboard. As stated, there are 8 relays in two rows of four, clearly marked Water Tap, Heater Fan Control and Fan Speed 1, 2, 3, 4. Bridge the offending relay, pins 30 to 87, and you have a very reasonable permanent patch without looking elsewhere. I can send more details and post more photos of the microprocessor board and replacement Microrelays if you wish. A section may be put in the Technical Library with data sheets and details if necessary. RT.     | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1682 Registered: 4-2003 |
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| Richard Treacy Grand Master Username: richard_treacy Post Number: 1683 Registered: 4-2003 |
Fan speed resistor block (fan speed resistor board). Note that the system I refer to applies only from SZ 20,000-series cars until the end of the SZ series. Earlier SZ cars and SY SSII/T2 cars have a more primitive but easily-repaired discrete-component setup and a different fan speed system altogether. RT.  | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1684 Registered: 4-2003 |
Note the 8 relays, in the picture above, in two rows of four, with some clearly marked Heater Tap, Heater Fan Control and Fan Speed 1, 2, 3, 4. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1685 Registered: 4-2003 |
A reconditioned Microprocessor board, by comparison, is based-priced at about AUD$1,000-AUD$1,500, depending upon the supplier, plus shipping, duty, GST/VAT/tax. A new one outright is base-priced at AUD$2,500-AUD$4,000. Likewise, a resistor block is base-priced at AUD$800-AUD$1,800. There is room there for secondhand, a patch or a repair, or even a modification to standard airconditioning rather than retaining the climate control ! | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 312 Registered: 6-2006 |
Lawrence, juar to be clear, are you saying that the A/C system stops blowing any air, or that it blows air but is no longer blowing cold air? Different faults usually. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1687 Registered: 4-2003 |
Paul, Lawrence, On Lawrence's post in this thread, the water tap Microrelay on the Microprocessor board has likely fused itself closed, opening the water tap fully whenever the climate control is turned on. Lawrence, pull out the Bosch Water Tap relay in the group of eight relays underbonnet located as described above. If it all goes cool, then that would rather confirm a Microrelay failure on the Microprocessor board. That would explain why it cools off when the systems is switched out for a while. If it were purely a refrigeration system problem, then most likely the system would not cool suffiently, but would not heat when asked to cool. The water tap and its main Bosch water tap relay would appear to be functioning, otherwise the air would be scorching hot from the outset. The earlier posts do apply, maybe apart from the fan speed resistor block and control system if the fans still function correctly. R. | |||
| Lawrence Heasman Experienced User Username: lheasman Post Number: 44 Registered: 5-2008 |
Thanks very much Richard for your comprehensive response. I will follow your advice to try and pin point the fault next weekend. | |||
| Dr. Omar M. Shams Yet to post message Username: omar Post Number: 1 Registered: 4-2009 |
Richard, I canot thank you enough for your comprehensive reply. If you are ever in Dubai, do let me know and the drinks will be on me. Since messing around with stuff i don't really understand, i now have a situation where there is absolutely no life whatsoever in 90% of the ac system. There is no +ve supply anywhere. The two fuses are ok but the compresor does not come on and the blowers are dead too. the servos seem to move though. Any ideas where to start looking? Thanks | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1688 Registered: 4-2003 |
OK. See the 30,000-series fan speeds control section C4-7: Work through http://rrtechnical.info/ or go straight to: http://rrtechnical.info/sz/30000/tsd5000wshop/hvac/c47.pdf The 20,000-series cars are almost identical, but the legend is different and the fan control supply is never disconnected from the relays. See http://rrtechnical.info/sz/sz87/ca.pdf for 20,000-series cars. For 30,000-Series cars, refer to the legend, component location and wiring diagrammes of http://rrtechnical.info/sz/30000/tsd5000wshop/hvac/c47.pdf . First, I would unplug the Fan Control Relay and Fan Speed Relays 1-4, located underbonnet near the left-hand bulkhead (items 40, 41, 42, 43 and 44). On the sockets, bridge Pin 87 of Fan Speed Relay 1 (item 44) to Pin 30 of the Fan Control Relay (item 40). The relays numbers are also marked on the relay socket frame; the frames are the same for 20k and 30k cars. The blowers should run at full speed with the ignition turned on (on 20,000-series cars it is regardless of the ignition key position). If not, then there is a fuse problem to start with – see 30A fuse, item 4), or even possibly all is not plugged in or wires are sheared. Please let us know the outcome for a next step. RT. | |||
| Dr. Omar M. Shams New User Username: omar Post Number: 2 Registered: 4-2009 |
Thanks for the reply. I can see now that there really needs to be a 12v supply to the yellow wires, and when i was looking at the car,there was not! Also the fuses looked good, so I will trace the wires and let you know. The car is in the garage and the garage closes on a Friday (for us a Friday is like a Sunday for you). I will be there at the crack of dawn on Saturday to trace the wires and let you know the outcome. Thanks again for your patience and perseverence. PS I have been driving my Wraith II with a blend of dot4 brake fluid with 10% castor oil for 6 months now and it feels great. I have never had better hydraulics!! | |||
| Omar Shams Unregistered guest Posted From: 86.96.228.89 |
Richard, I cannot thank you enough for your informative reply. I am miles ahead of the game already thanks to you. if you ever visit Dubai, let me know, I owe you a crate of beers. Today I looked at the AC system and this time.... ever part of it is dead. No life at any of the relays and the compressor does not engage. It is probably a fuse or something like that. Where would be a good starting point to get a source of power to feed the whole system? Also should the LED be on on the microprocessor board? Incidenatlly, the car is a 1990 Turbo R. (Message approved by david_gore) | |||
| Omar Unregistered guest Posted From: 86.96.227.93 |
Richard, i cannot thank you enough for the valuable information. I will try out your proposed suggestions on my Bentley and revert. By the way, if you are interested, I have successfully converted my Silver Wraith II to run on a blend of ordinary brake fluid and 10% castor oil instead of RR363. The car feels better than my previuos Shadow that ran exclusively on RR363. (Message approved by david_gore) | |||
| David Gore Moderator Username: david_gore Post Number: 882 Registered: 4-2003 |
Hi Omar, My apologies for the delay in approving your post of 27th March - have been away all week with no internet access. Kind regards David | |||
| Dr. Omar M. Shams New User Username: omar Post Number: 8 Registered: 4-2009 |
Richard, I went to the garage where they are doing lots of work on my Turbo R. The water pump was out, the hydraulic pumps were both removed, the rocker covers were removed........... the list goes on. I did some tests and found that the 30A fuse is live at both ends, but the yellow wires around all the relays for fan speed and ACU control are dead. I will now trace the wires back to the fuse to see where the break is. once I find it, I will revert. Thanks again for your input, it is most appreciated. | |||
| Dr. Omar M. Shams Experienced User Username: omar Post Number: 19 Registered: 4-2009 |
Richard, Thank you for your patience with me on this subject. I followed your instructions below as detailed before viz: First, I would unplug the Fan Control Relay and Fan Speed Relays 1-4, located underbonnet near the left-hand bulkhead (items 40, 41, 42, 43 and 44). On the sockets, bridge Pin 87 of Fan Speed Relay 1 (item 44) to Pin 30 of the Fan Control Relay (item 40). The relays numbers are also marked on the relay socket frame; the frames are the same for 20k and 30k cars. The blowers should run at full speed with the ignition turned on. hey presto the fans did run ... but at that anaemic speed. I then disconnected one blower at a time with the car running and the ac on. hey presto; the amount of air in the cabin reminded me of my Shadow 1. I did the same test for the other blower and that too ran at a healthy fast pace delivering the quantity of air I am seeking. If both blowers run at that fast speed then there will be plenty of cool air in the cabin to allow me to run the car during our summer months. If not, then I will be forced to put the old girl away with the other cars and hire a Toyota Yaris to see me through the hot UAE summer. any ideas what I should do next? the resistor block appears to be ok from the crude testing I have carried out so far. | |||
| Duane Ridenour Unregistered guest Posted From: 162.204.108.226 |
Richard, I have a 1986 Silver Spur NAG-13418 where the heater/AC fan does not come on. The compressor will kick in when the AC is selected and, if direct power is applied to the fan, it will run. I read your posts about the 20,000 series SZ, since my VIN is 13148, I assume that your comment about earlier series will apply to me. I have checked the fuses and the relays. Do you have information or can you point me in the direction to fix my fan issue? Thank you in advance, Duane (Message approved by david_gore) | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2958 Registered: 4-2003 |
There seem to be open issues here. Omar - does the problem persist ? Duane - yours is an earlier car with a diode block rather than a resistor block. Regardless, how did you activate the fans. Did you plug the relays ? The answer will help to determine the way to diagnose the matter. RT. | |||
| Omar M. Shams Grand Master Username: omar Post Number: 379 Registered: 4-2009 |
goodnes me!! that was literally years ago. I have since had to make all sorts of changes to the AC system. I cant remember what we did in the end - i may have replaced the microprocessor and a few relays and it all worked again. Sorry I cant be of much use. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2959 Registered: 4-2003 |
Omar. Four and a half years ago in fact. No wonder it is all forgotten. RT. | |||
| Duane Ridenour New User Username: kg4ibj Post Number: 3 Registered: 12-2013 |
Richard - unplugged the yellow wire from the fan (leaving the ground attached) and touched the connection on the fan with 12V. The fan worked. Did the same on the passenger side fan. I can hear the servos moving, when moving I get air from the defroster vents unless I press the Facia button and the cold or hot air (based on the setting of the dials) will come out both the round and rectangle vents. Thanks for the response. | |||
| Duane Ridenour New User Username: kg4ibj Post Number: 4 Registered: 12-2013 |
Update - I have pulled all the relays on the driver's side (LH) behind the knee roll and they all "click" when power is supplied. There are an additional three behind the speedometer that I also pulled which were operating correctly. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2995 Registered: 4-2003 |
If you plug the relays, does the fan come on ? That means connecting a wire between pins 30 and 87 on the relay sockets. If not, it would certainly indicate a failed diode block. RT. | |||
| Duane Ridenour New User Username: kg4ibj Post Number: 5 Registered: 12-2013 |
Thanks for the info. I will give that a try this morning and report my results. From my research, it appears that an article on rrtechnical.info states that each diode on the board can be replaced with a 1N4007, except for one Zener? This seems too easy. | |||
| Duane Ridenour New User Username: kg4ibj Post Number: 6 Registered: 12-2013 |
Okay, jumped pins 30 and 87 (at the relay socket) on the ACU control, fan control and another that I can't remember except it begins with Lower. The fans do not come on. In the Workshop Manual the first test says to check the Orange/Blue wire at the ACU switch. My switch does not have an Orange/Blue wire (or a Blue/Orange wire). Now I'm even more confused. | |||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2996 Registered: 4-2003 |
Duane, that is the diode board to which you refer. I mean the diode block. It is a heat sink affair about 10cmx10cmx4cm. See http://rrtechnical.info/sz/sz80/c.pdf item 16 in the first diagramme. RT. | |||
| Duane Ridenour New User Username: kg4ibj Post Number: 8 Registered: 12-2013 |
The heat sink item is what my mechanic said needed to be replaced. It was and there was no change in the operation of the fans. I can hear the servos moving as the switch is turned to low, auto, high and defrost. | |||
| Robin Hall New User Username: bombguy54 Post Number: 5 Registered: 6-2013 |
Turbo R 27723 I, too, have an issue with my climate control system = non-operational. I have studied the schematic in the Technical Library. - I have >12v at the Microprocessor board power points, left and right incoming from the "18" pin plugs. Clean ground to transmission tunnel. -All climate control relays either tested good or have been replaced with relays with FWDs (Freewheeling Diodes). Voltage at relay points at/near/slightly over 12v. - Car warmed to 40C; confirmed by a jumper wire between relay terminal “30” and “87” on the Compressor Clutch Relay base. The clutch kicks in. BTW, AC compressor will not kick in via relay; must be jumped. - Jumper wire between terminal “30” and “87” on the Air Conditioning Fan Control relay base. This jumper provides power to “30” of the Fan relays. Fans run normally increasing/slowing relative to Climate Control Switch position, telling me that the fan relay coil circuit are finding ground through the Microprocessor board, per design. Fans will not run with a relay installed in the AC Fan Control relay plug = relay base must also be jumped. - Water tap relay functions normally; no jumper required. In “Demister” position (knob turned far right), wheels in the “Red” = fans run slowly but I think that is because the current ambient temp is ~27C. Demister blows slow heat to the windshield, fan speed being controlled by the Temperature Control side of the Microprocessor board(?) I can see via the schematic that all the relay coil grounds are sourced through the Microprocessor board but what I don’t know is from what source within the board is it that permits that current flow. Per Richard Treacy’s post of 26 April 2009, my suspicion is that one, or more, of the control board relays has failed. The relays on my board are labeled “OUAZ-SH-112D” and replacements are available through Mouser Electronics, brand name TE Connectivity/OEG, for $1.71 USD each. I don’t have a schematic of the Microprocessor board so I don’t know which board relay does what. No problem. I’ll take Mr. Treacy’s recommendation and replace them all. I’m prepared to undertake this effort but I just needed the input from those vastly more experienced than myself to ensure I’ve covered all the bases before replacement of the microprocessor board relays. So, please hold my hand and tell me everything is going to be OK. TIA for any and all assistance with this issue. } | |||
| michael vass Frequent User Username: mikebentleyturbo2 Post Number: 88 Registered: 7-2015 |
Aloha Robin Please don't take this the wrong way ,it sounds like you know more than me about this than me anyway, but you have got sufficient gas pressure ? Just that sometimes we can miss these things  have you still R12 or updated gas? Best regards mike | |||
| Edward Mckinley New User Username: ed_mckinley Post Number: 7 Registered: 10-2019 |
Would anyone happen to know the current part number for the microrelays on the HVAC microprocessor board? Mr. Treacy's post from above states that there are two kinds. The microrelay's on my board have most of the print gone off them, all I can make out is SH-112D and 12vDC. | |||
| Edward Mckinley New User Username: ed_mckinley Post Number: 8 Registered: 10-2019 |
Here is the board from my car 89 Corniche
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| Edward Mckinley New User Username: ed_mckinley Post Number: 9 Registered: 10-2019 |
Trying again  |
pic of original board