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Old 05-05-2007, 08:48 PM #16
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Quote:
Originally posted by a77boy
Mechanical relay as far as I know. I managed to take apart the relay next to it, EFI i think. It is a little different, but It is definetly mechanical. The magnetic clutch relay should be the same. As stated before, I simply banged it on my counter top and it has been working for two months. :-)
I remember that from your earlier post, so I suspected it was a mechanical relay, but wasn't sure. Banging a solid state relay shouldn't 'help' it at all. I'll have to look at the contacts when I operate on mine. I suspect they will either have arc deposits which are increasing the resistance across them to the point that they won't activate the mag clutch, or they are welded shut and won't open.
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Old 05-05-2007, 08:56 PM #17
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The one relay that I was able to open was no problem, I simply had to pry it open with a small screwdriver. The MGNT CLTCH relay is different, it is completely sealed with some sort of epoxy type substance. Good luck on opening that one. Let me know if you can.
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Old 05-06-2007, 08:43 AM #18
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Relays electrically isolate the control circuit (low current) from the circuit being controlled (the a/c compressor clutch, which is higher current).

My guess is that the relay was not sized correctly for the A/C compressor clutch. But I would think that a fuse would blow before the relay crapping out?

The control side of the relay could also be failing? Most bosch relays need 8 volts to energize the coil (which pulls the contacts) and the Drop-out voltage is usually around 1 to 5 volts. So maybe the coil is not sized correctly
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Old 05-06-2007, 08:55 AM #19
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Looking at the relay; it is very very small. Almost too small for a coil? Maybe you are correct, TechWrench, about the solid state type being used. Below is a picture of a typical found in my other two vehicles (not the Toy)
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Old 05-06-2007, 12:04 PM #20
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Quote:
Originally posted by greasefingers
Looking at the relay; it is very very small. Almost too small for a coil? Maybe you are correct, TechWrench, about the solid state type being used. Below is a picture of a typical found in my other two vehicles (not the Toy)
The MG CLT relay we are discussing only has a 4 prong base. Therefore, it can only have one set of contacts. (two prongs for the controlled circuit, and two for the coil. They are drawn, in the prints, with the contacts in the normally open position, which is the de-energized state. So, the contacts should close when the coil is energized. If the base of the relay is epoxy sealed, that tends to make me think it is a solid state relay. The prints indicate it is a 12 vdc coil, and a ground is provided by the ECM to activate the relay coil. From my experience with relays at work, mechanical relays 'usually' work, or they don't. When they fail, it is usually a mechanical failure. SSRs on the other hand can fail intermittantly for a while before they quit completely. I should receive the replacement relay later this week, and one way or another, I WILL get the cover off that relay to see which type it is.
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Old 05-06-2007, 01:48 PM #21
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haha,, sweet!!!! I am very interested to see what the hells in there!! Keep us posted (uhh excuse the pun)
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Old 05-08-2007, 09:57 AM #22
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Update; Patrznet just notified me that this relay is on national backorder, and will not be available for at least one month.

I tried the local Toyota dealer, they want $70.64, and it will take 2/3 days to get it.

Fortunately, the relay I swiped from the fog lights is working, so I guess I will be waiting a while for the new one.
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Old 05-08-2007, 02:18 PM #23
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Hopefully all will work fine during the summer months
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Old 05-08-2007, 05:38 PM #24
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Yup I diagnosed my boss
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Old 05-09-2007, 01:17 PM #25
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I got the same 'national back-order' message from Partznet this morning after wondering why I hadn't received my parts yet. I just took a look at the wiring manual and believe it points to the cause of the premature relay failure. This relay is switching an inductive load but doesn't have a mechanism to absorb the "kick back" EMF produced when the load is de-energized. The energy very likely escapes the system by arc'ing across the open relay switch contacts.

Over time, this design is likely to cause the relay contacts to fail to properly conduct current. Possible failure modes are stuck open or intermittent stuck open, or even stuck closed. Any of these faults will result in a failure of the compressor lock sensor circuit. The A/C control module will respond by blinking the light and shutting down the compressor. If your failure was the stuck closed type, banging the relay on the counter could bring it back to life (temporarily).

I'm going to try swapping the relay with my fog lights (until my new relay comes) AND adding a reverse polarity diode across the switch contacts to dump the inductive load back to the supply. My guess is the new relay has the diode built in or it uses a more durable switch contact material/size so it can withstand this kind of punishment longer.

UPDATE: See later posts -- you need to install the diode between pin #3 and GND, not as pictured in the next post.

Last edited by rando; 05-09-2007 at 10:18 PM.
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Old 05-09-2007, 02:39 PM #26
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Here's the intended orientation of the protection diode. I don't advise anyone else try this since my relay didn't survive the heat from the soldering iron -- ended up dead completely.

UPDATE: This circuit doesn't work -- see later posts for the correct solution.
Attached Images
A/C light flashing??-protection-diode-jpg 

Last edited by rando; 05-09-2007 at 10:19 PM.
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Old 05-09-2007, 02:44 PM #27
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Since my relay is now completely dead, I thought I'd go ahead and confirm a few theories.

A) This is a mechanical relay -- OK, I already knew that since I could hear it clicking on/off on the bench.

B) The charring around the relay contacts supports the theory that arcing is causing the premature failure. A diode as pictured above would solve this problem.
Attached Images
A/C light flashing??-relay-contact-charring-jpg 

Last edited by rando; 05-11-2007 at 05:39 AM.
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Old 05-09-2007, 04:40 PM #28
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Quote:
Originally posted by rando

B) The charring around the relay contacts supports the theory that arc'ing is causing the premature failure. A diode as pictured above would solve this problem.
Thanks for the disection Rando. Good info.
I don't have a relay failure yet but am out of warranty so I would like to do some prevention.
Since the durable relay is hard to get would it help to splice the diode somewhere else in the circuit (due to the solder heat at the relay)? What are the specs on the diode you suggest?
Thanks again.
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Old 05-09-2007, 06:43 PM #29
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Any general purpose rectifier should be fine (ex: 1N400x series). I used a 1N4005 equivalent part. It's rated at 1A (far more than the inductor kickback will produce) and 600V reverse voltage tolerance which means it should survive the nasty load load dumps and other transients that appear from time to time on the automotive alternator/battery supply rail.

I went ahead and moved the Fogs relay over since it's unlikely I'll need them anytime soon. For now, I just went ahead and installed the diode as pictured -- just without the solder (i.e. surface tension only). When I get some more time, I'll look for an easy and safe spot to install it. The wiring manual suggests there are a couple of junctions in that circuit. The A2 socket at the compressor clutch / sensor might be a viable option -- in this case you'd hook the diode anode to ground (UDPATE: In fact this is the proper solution) .

An obvious alternative would be to build a small harness including the diode to fit between the relay and the socket, using blade connectors.

Last edited by rando; 05-11-2007 at 05:52 AM.
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Old 05-09-2007, 07:58 PM #30
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Quote:
Originally posted by rando
Since my relay is now completely dead, I thought I'd go ahead and confirm a few theories.

A) This is a mechanical relay -- OK, I already knew that since I could hear it clicking on/off on the bench.

B) The charring around the relay contacts supports the theory that arc'ing is causing the premature failure. A diode as pictured above would solve this problem.
Nice detective work. I'm not used to seeing mechanical relays sealed like that, Thats why I thought it might be a SSR. I guess it is to keep them clean given the environment they work in. Though some of the other relays in the box aren't sealed, in any case. Those contacts are, with out a doubt, burnt. I'm hoping the fog light relay holds out until the new relay is available again. I think the original A/C relay lasted 3 years, so I hope we have some time before the next one fries.
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