A/C help

[Arthur Dalton]

Originally Posted by ggenovez

Cool. Thanks. I'll try it tonight.

Also jumping 30-87a should kick on the clutch right?

Same thing..I just am having you test for power at the relay b/c then you will know the problem is the relay or the comp. magnet if you have power to relay. So, jumping 30/87a bypasses relay and will brring that power to comp clutch.
If no power to relay, you have to go back the other way [ which is where I think you will find the problem b/c you have no Indicator lamp. ] But first see what you have at relay.

[ggenovez]

Agreed.

Looking at the schematic and going through the jobs process, item 7 (changeover switch) activates the indicator, temp switch to relay, and the cooling motor.

Changeover switch must be getting power since the fan is working ...

Ok. thanks.

[ctaylor738]

I fired up my CD. Doesn't the blower switch ground the relay and the clutch? When that ground happens the relay connects 30 to 87a and George finally gets cool air.

[ggenovez]

AH HA!!!! I am getting voltage through termina 30. And jumped it to 87a, got a small shock, some sparks and a loud clank from the clutch!!!!!

Ok, any idea who else used this relay? I'm hoping to find something that will work from my local autoparts store. I'm dying here, it's in the mid 90's still.

Can't wait for some global cool. or at least some local cooling in my car!!!

Thanks for the walk through Chuck.

[Arthur Dalton]

Originally Posted by ctaylor738

I fired up my CD. Doesn't the blower switch ground the relay and the clutch? When that ground happens the relay connects 30 to 87a and George finally gets cool air.

Is that how your CD shows it???

The ground for clutch, relay,and blower sw are just common grounds.

Using his schematic, you will notice that the relay contacts for 30/87a are normally CLOSED [ when there is NO power to the relays activation coil].
When the relay coil does get power, it does not close 30/87a, but rather it OPENS 30/87a contacts, thus releasing the comp clutch magnet. This happens when the feed from the starter circuit feeds the relays coil pos + side. That is to Interrupt the comp from being ON while the starter is attempting to turn ther engine over.
The tip-off here is terminal 87a. The "a" on Bosch relays means that circuit is CLOSED when the relay has NO POWER to coil. IT is terminal #87 that is switched w/power on Bosch Relays, not 87a. Notice that term. 87 is NOT used b/c this circuit is not a relay feed circuit, it is a relay disconnect circuit.

If he gets comp clutch when jumping 30/87a, it is b/c those contacts are bad, not b/c the relay is not pulling them in. They are already IN w/o power to the coil side.

Possibly you have a different schematic ?
Or maybe a clearer one..

[Arthur Dalton]

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Very good..
That means that the normally closed contact set for 30/87a in the relay are fried.
...but , if you read my other two post, you will note that this is not a standard 4 prong relay, but rather a Normally closed relay [ meaning it is a 5 pin relay]
You can use any standard 5 pin,12 volt/30 Amp relay [ radio shack has a nice one with a mount tab right on it] ..the trick is you have to use terminal 87a for the compressor clutch feed , not the standard terminal 87. Terminal 87 is not used on this type of circuit.
You may want to pop the top on your relay and you will seee what I mean as far as those contacts are closed when the relay is not hooked up. That is the way I see this circuit working.
Your schematic is not legible on this end , but I should be correct in assuming that terminal 87 is not connected to anything, but the comp clutch is connected to 87a ??

If you get a replacement relay, just check the terminal #s..... you know you have the correct one if it has an 87a terminal. If it does not, it will not work correctly.
Must have 30,85/86 for coil, and 87/87a for contacts. [5 pins. If the relay is a 4 pin, it will have #87, but not have the #87a, which it must have for your circuit]

This site explains the workings of the relay contacts I am referring to .

http://www.the12volt.com/relays/relays.asp

[ctaylor738]

When I got a clear version of the schematic, it looked to me like this is one of those cases where ground is switched to ground the clutch and make the relay engage. 30 is powered by the pressure switch.

Otherwise the compressor would come on without the fan switch.

But I admit to being schematically-challenged.

Anyway, these relays are (or at least were) not very expensive.

[Arthur Dalton]

If you look at the relay, you will see that 30 is connected to 87a in normal state [ meaning everthing is OFF] , which then feeds the clutch. Once the relay coil is energized, you no longer have any power to the clutch b/c the contacts from 30 to 87a are now pulled Open, resulting in no voltage to clutch. You can ground the other side of the clutch til doomsday and it will not work until 30 is connected to 87a.
The 30 feed can not happen until the a/c control is in Cooling position.

You are corrct on the relays ..cheap..he need a spdt with an 87a normally closed therminal and he will be OK to cool [ providing he has refrig, etc..]

I see the Bosch ones on ebay all the time. He could even chance it with the jumper , but he would always have to be sure he turned off the a/c everytime he turned the car off and then turn it back on after start.

[ggenovez]

My Apologies for the document. There is a limitation to size on this website. Here is another document that may look better.

If not email me and I'll send you the complete pdf back.

Again I must apologize, I must be too tired to understand what's going on. Was the 30-87a a valid test? would jumpering the 2 together resolve my issue temporarly until I can get a relay? would I need to disconnect the relay from the connector and jump the 2?

I'll be going back and reading this in detail after I get some zzzzzzzzzzzzzzzzzz.

Thanks again to everybody...

[Arthur Dalton]

Perfect...now I can read the terminal #s.
OK
They are right like I said they were , so..
You can take the relay out and just jumper 30 to 87a.
The only thing is, make sure you turn the a/c controls and temp sw off each time before you turn off the engine and don't turn it back on 'til you start the car.
The relay does this automatically so the owner does not have to worry about it.
The main reason is they don't want the a/c clutch engaged until the starter
is out of the circuit.
The relay is simply an a/c clutch Interupt device, not an a/c ON device. Just the opposite as one would assume.

For those following the thread , note wire feed circuit 50 [Benz #50 is always starter circuit on all Benz ] to 86 of relay coil..This is starter circuit from the solinoid down at the starter..So, when starter is cranking, you can see how this relay pulls in, thereby interupting the power to the ac clutch by opening 30/87a. Once the car starts and the key is released to RUN position, the relay goes back to normal mode and the a/c clutch can now operate.
That should do it......................

[ctaylor738]

I see the flow from the 16 amp fuse to 30 via the pressure switch, the indicator lamp and the AC blower. But IME, the compressor does not engage until you turn the blower on. How does this work if 85 is a hard-wired ground?

I am not sure that you can condemn the relay just yet. With the AC switch and blower on, are you getting ground on 85?

Just to satisfy my curiosity, do you lose the ground if you turn the blower off?

[Arthur Dalton]

>

NO..........Your confusion is you think this relay is a switched ground circuit..it is not.

And you also state that the 30/87a contacts pull in when relay coil is energized.. that is incorrect.
They are connected when the relay is OFF. Look at the relay contacts/schematic..[ schematics are drawn with all switching components in OFF positions , unless notationed ]

The contacts that pull IN/ON with relay energized are 30/87..which you can see are not used in this type of interupt circuit.

I do believe that I have found the reason you are confusing your switched ground theory . The Blower motor uses a sw/gnd thru the blower switch to complete the blower circuit, but that has nothing to do with the clutch relay's ground..look close and you will see the relay/clutch grounds are OUTSIDE the blower switch. It is therefore a COMMON GROUND point for both the clutch magnet and the relay terminal #85, along with also being used for outside blower sw grounding point. Nothing to do with the blower control except to be physcially connected to the outside ground there. Both a/c relay and clutch are grounded regardless of any blower control position. Clutch and blower are Different circuits.

And 30 is supplied 12v feed from the temp sw via Heat/AC changeover sw, not a pressure switch. The A/C switch is fed from the Blower sw, but that is is an independant set of contacts inside the blower switch. That is why comp clutch won't work until the blower sw is ON..not b/c the blower sw is grounding a relay.
If you look closely at the schematics internals of the Blower sw., you can see there are TWO contact swipe arms....one has a ground link and one does not..they are two different circuits..one for blower fan motor/speed and one for a/c control feed..completely ISOLATED from one another inside the single switch body. In lay terms, the blower switch assembly houses TWO different switches, each seperate from the other in function and electricaly isolated from one another. One functions/controls the fan circuit, the other functions/controls the a/c feed.
That's about it.....................

Let me know if this helps .

[ctaylor738]

Got it. I totally missed that jog that the feed from the 16 amp fuse takes through the blower switch.

Thanks for helping the schematically challenged.

[ggenovez]

Hey Chuck,

I can attest that 87 is not connected to ground. In fact, thought there are 5 pins out of the relay, only 4 are attached.

My understanding, and arthur please correct me if I am wrong, but with the limitations of only 8 and 16 amp fuses, having the AC and starter run at the same time draws too many amps, so 86 I belive connects to the starter switch. When the ignition is kicked on, 86 is energized and the internal coil pulls the connection from 30 to 87a to 30 to 87 which is connected to nothing, and breaks the contact with the clutch so the AC turns off.

Once you let go of the starter switch, relay goes from 87 to 87a and the clutch kicks on again.

Ok, I jumped the switch and ran the AC, and still no air. I'm going to go back and check the wire to the AC clutch and make sure I'm getting voltage.

Thanks again to everybody...

George

[Arthur Dalton]

Originally Posted by ctaylor738

Got it. I totally missed that jog that the feed from the 16 amp fuse takes through the blower switch.

Thanks for helping the schematically challenged.

I knew you would see it as soon as you took a closer look..

To help anyone out on these circuits, one will find them most to be very basic, simple circuits with the trick to tracing them out is to break down the schematic into eachs parts funtion..they are usually a few circuits combined into what looks like a maze, but it is just a simple 'Follow each circuit from feed fuse , thru components, to ground. That completes each circuit.
A magic marker helps..and for those not electrically savy, I tell them to compare the wires to water plumbing..that help the mind follow the Flow more naturally.... ya can;t see 'dem 'Lecrons"...)

I uses to be able to until I got a Blast of the Kriptonite..that slowed me right down


Anyway, back to the post...if the jumper from 30 to 87a worked , you have a bad connection inside the relay...might even want to pop the top and clean the points.......sometimes it s just dirt on an old relay.