| Author | Message | ||
     lucien mc fadden New User Username: lucienm Post Number: 9 Registered: 7-2005 |
I replaced all the diodes in my 76 shadow. I don't really know what they are for-can someone explain them to me? The top diode:bullseye/clutch-is hot to the touch-is this normal? #3 diode(from top)-U QTY.FLAY SHUT gives no reading to my amp meter-nor does #4(from top)-L.H.REC. R.H.REC. (sorry,but i don't understand what these abbreviations are for.... | ||
| David Gore Moderator Username: david_gore Post Number: 747 Registered: 4-2003 |
Hi Lucien, If the diode is hot, it means one of 3 possibilities: 1. the diode has been installed back to front and is passing current instead of stopping it which is its intended function. 2. The diode was correctly installed and has failed. 3. The diode connections on the back of the fuse board are faulty/loose/poorly soldered causing the overheating problem. The only way of testing the diodes is to remove them from the board and test them with a multimeter set to measure resistance. A good diode will show no resistance measured in one direction and infinite resistance when measured in the other. The purpose of the diodes is to block unwanted voltages getting to electrical components when specific parts of the car electrics are in operation. | ||
| Paul Yorke Frequent User Username: paul_yorke Post Number: 69 Registered: 6-2006 |
Luciene, These diodes are for the air conditioning flap actuators mainly. When you operate the heater / air con controls - different diodes will be live. One air conditioning / heater switch position can operate more than one actuator, Say left hand recirculatory flap and R(ight) H(and) REC(irculatory flap). These flaps need to be closed or open at the same time. Because of the way that the actuators work ( and because they do not rotate at the same speed etc ) if the same feed was sent to both actuators they would feed each other and would keep turning forever. The diodes split the feed from the switch so each one has an independent feed. Just imagine the diodes are a one way valve for electricity. Obviously they need to be fitted in the correct direction. If an actuator is stuck it will also keep taking a load and may warm up the diode. Recirc. actuators (above the outside foot of the driver and front passenger ) have small rubber bushes that fail and allow the flap to fall and jam. You will need to lay in the foot well - looking up to see the actuators and flaps. (bushes are fitted from the outside after removing blower fans etc.) The Air Con valve often seizes so the actuator cannot turn. The heater tap and air con valve near it should open and close together but opposite. | ||
| John Kilkenny Experienced User Username: john_kilkenny Post Number: 46 Registered: 6-2005 |
Hello Lucien, The seven diodes (diodes are electrical devices which allow current in one direction and not in the other) are used to prevent unwanted connections between the various switch segments of the upper system, for cars with air conditioning. The #3 diode (Upper Quantity Flap Shut) prevents unwanted feedback when the selection of any Aircon position closes the upper quantity flap, preventing cold air to the windscreen. The L.H.REC and R.H.REC refer to the Recirculator Flaps on each side of the car which allow air to be recirculated when the Airconditioner is operated. Proper testing of diodes should be done with a multimeter having a diode test position. You can buy one for fifteen dollars or so from Tandy or Dick Smith. This will show the forward bias reading which is about 0.5 volts and infinity for the reverse. Diodes 1,2,3,5,and 6 can be tested in circuit. Diodes 4 and 7 need to be disconnected before testing. Regarding the heating of the top diode it is difficult to see how a single reversed or shorted diode could do it. This diode allows the Bullseye Flap to direct cool ait through the circular outlets. Was everything working OK before you changed the diodes ? If the answer is yes discard all the diodes and replace with new ones, making sure the polarity is correct. Finally there is no value in regular replacement of diodes; you wouldn't do it for your car radio so why do it for the actuator diodes. Check them every couple of years if you want to, or if you suspect a problem with an actuator. Best regards, John | ||
| bob uk Unregistered guest Posted From: client-81-108-181-227.brig.adsl.tesco.net |
Diodes are solid state( no moving parts so wear cannot happen.) These are one of those parts that are never changed until they fail. Condenser in dizzy are often changed as a matter of course while servicing. I have only ever seen one failed condenser that failed while the vehicle was being used. A Ford Transit which would just about start and not rev. All the other broken condensers were caused by the mechanic or owner pulling it about when the engine won't start. Eventually the engine starts after the points and condenser have been changed and the fault put down to a dodgy condenser when the engine was probaly flooded. It goes like this--- the mechanic checks for fuel compression and sparks but the engine will not start so the mechanic get suspicious of the condenser ( a lot of mechanics do not fully understand what the condenser actually does ) By the time the condenser has been fitted the engine has dried out and it fires thus re-inforcing the idea that condensers are unreliable when in reality they are the most reliable bit of the Kettering system (Message approved by david_gore) | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 1282 Registered: 4-2003 |
Whilst the above is largely true, don’t forget that if you pay 20c for a diode it is too expensive. So not to annoy the wholesaler, I buy them in ribbons of 300 at 4 cents each. At that price, it is best just to replace them all if in doubt or whenever working in the areas where they are located. A fair use-by date is 15 years. I only test the used ones once removed out of curiosity before throwing them away. If in doubt, throw it out, Some diodes will last 5 years and some 60 years. They do age and not work properly in some locations after some years. The diodes and transistors in the SY coolant level sensor were notorious for having a half-life of 10 years until replaced by newer semiconductors of superior quality. Likewise, the driver’s door courtesy lamp on later SZ cars usually failed at 8 years until replaced by a superior new one. At 48 cents for the lot, these diodes will not break the bank.  And here is the unreliable diode on the SZ coutesy lamp:  | ||
| lucien mc fadden New User Username: lucienm Post Number: 10 Registered: 7-2005 |
well, i feel stupid!! the "hot" diode was indeed reversed-even with my reading glasses i put it in backwards! Thanks everyone for your kind assistance! :} |
