Relay Experts
Thread Starter
Intermediate
Joined: Jun 2008
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Relay Experts
I need RELAY class 101:
This is not on my Corvette.
I have a 4 post A/C relay that I can not get to function. I even replaced it and same problem.
It has 85 86 87 30 prongs. I have 12 volts to 3 of the 4. Why would the relay not turn on? I know they can not both be bad. And I also tried the same relay off the fan motor. If I remove the relay and jump the wires the A/C clutch turns on.
I am pulling what little hairs I have left out of my head
Second question, why is there no ground going to a relay? I never thought about it until today
This is not on my Corvette.
I have a 4 post A/C relay that I can not get to function. I even replaced it and same problem.
It has 85 86 87 30 prongs. I have 12 volts to 3 of the 4. Why would the relay not turn on? I know they can not both be bad. And I also tried the same relay off the fan motor. If I remove the relay and jump the wires the A/C clutch turns on.
I am pulling what little hairs I have left out of my head
Second question, why is there no ground going to a relay? I never thought about it until today
Safety Car
Joined: Oct 2007
Posts: 3,816
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From: :45 minutes from everywhere / E-I-E-I-O
Here's a few FSM schematics of fan relays, and the tests (pics) I did to both of them - starting at post 111. I'm guessin' that all relays are similar...
http://forums.corvetteforum.com/show....php?t=2069247
Otherwise, Mr. suncr is the a/c guru. Wait for him to ring in...
http://forums.corvetteforum.com/show....php?t=2069247
Otherwise, Mr. suncr is the a/c guru. Wait for him to ring in...
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
I need RELAY class 101:
This is not on my Corvette.
I have a 4 post A/C relay that I can not get to function. I even replaced it and same problem.
It has 85 86 87 30 prongs. I have 12 volts to 3 of the 4. Why would the relay not turn on? I know they can not both be bad. And I also tried the same relay off the fan motor. If I remove the relay and jump the wires the A/C clutch turns on.
I am pulling what little hairs I have left out of my head
Second question, why is there no ground going to a relay? I never thought about it until today
This is not on my Corvette.
I have a 4 post A/C relay that I can not get to function. I even replaced it and same problem.
It has 85 86 87 30 prongs. I have 12 volts to 3 of the 4. Why would the relay not turn on? I know they can not both be bad. And I also tried the same relay off the fan motor. If I remove the relay and jump the wires the A/C clutch turns on.
I am pulling what little hairs I have left out of my head
Second question, why is there no ground going to a relay? I never thought about it until today
Looking at Schrades WD it does show 1 feed to the coil and 1 feed to the contact that when closed turns the fan on(feeds) and the other side of the fan goes to ground. It also shows a hot feed to the coil and the other side going to the PCM which provides the ground to complete the coil circuit. In short before it is turned on only 2 wires are hot the other 2 are open(1 will show the fan resistance the other should show an open to the PCM)
Last edited by Redeasysport; Aug 1, 2008 at 05:44 PM.
Thread Starter
Intermediate
Joined: Jun 2008
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In my first post I said this is not my Corvette. Teen Daughters car.
In the attachment by the thumb print there is a circle of the relay.
Pink, Pink, and Green/white all have 12 volts. I inserted prob into each wire and ran the ground probe to ground.
This is my first attachment
In the attachment by the thumb print there is a circle of the relay.
Pink, Pink, and Green/white all have 12 volts. I inserted prob into each wire and ran the ground probe to ground.
This is my first attachment
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
In automotive relay wiring, the relay coil is wired one of two ways.
1. One coil wire goes to 12v (usually 12v from the ign switch and only when the ign sw is in run) and the other coil wire goes to the device that turns on the relay and it does so by grounding this coil wire.
2. One coil wire goes to ground and the device that turns on the relay supplies 12v to it.
You have the schematic, see where both coil wires go and see if you get 12v on one relay coil wire and ground on the other, OR, see if one coil wire is grounded (check the physical ground connection) and if 12v is supplied from the source.
1. One coil wire goes to 12v (usually 12v from the ign switch and only when the ign sw is in run) and the other coil wire goes to the device that turns on the relay and it does so by grounding this coil wire.
2. One coil wire goes to ground and the device that turns on the relay supplies 12v to it.
You have the schematic, see where both coil wires go and see if you get 12v on one relay coil wire and ground on the other, OR, see if one coil wire is grounded (check the physical ground connection) and if 12v is supplied from the source.
Last edited by jfb; Aug 1, 2008 at 09:27 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
No, automobiles have the negative terminal of the battery connected to the frame. You measure volts with a voltmeter with the negative probe on ground (frame), so any grounded wire you put the positive voltmeter probe on will measure 0 volts, NOT -12v.
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Thread Starter
Intermediate
Joined: Jun 2008
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Still lost why I don't understand
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
OK how are you measuring the voltage from the wire to ground? The dark green/white should read 12V but from what I am seeing your PCM is not calling(grounding) the coil to turn on thus no voltage to the Drk Grn to the clutch. I assume that when you jumper the Pnk to Drk Grn the clutch comes on correct? Even though you have 12V on both sides of the coil you are not getting a complete circuit. Check your wiring at the PCM on the Drk Grn /Wht either the pin is not in all the way , corroded or the PCM has an issue from what your wiring diagram shows. It does not appear to be a clutch relay issue from what you post.
It is possible that some other issue is not allowing the PCM to turn on the coil too.It takes all the inputs and decides if it should turn on the clutch.You are showing an AC sensor that may not be working and most systems have pressure switches that have to be correct(although not shown) for the system to turn on. The PCM checks them all before turning on the clutch.
It is possible that some other issue is not allowing the PCM to turn on the coil too.It takes all the inputs and decides if it should turn on the clutch.You are showing an AC sensor that may not be working and most systems have pressure switches that have to be correct(although not shown) for the system to turn on. The PCM checks them all before turning on the clutch.
Last edited by Redeasysport; Aug 1, 2008 at 11:25 PM.
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Intermediate
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I am just sticking the probe up each wire while it is pluged into the relay. I am sticking the neg probe to ground on the engine.
When the A/C switch in the car is turned off the green/white wire has no voltage. YES when I jumper the Pnk to Drk Grn the clutch comes on.
I guess I am confused because I read the schematic as both Pink wires are always 12 volts.
When the A/C switch in the car is turned off the green/white wire has no voltage. YES when I jumper the Pnk to Drk Grn the clutch comes on.
I guess I am confused because I read the schematic as both Pink wires are always 12 volts.
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Yes that is what it says as long as the fuse is good.
Last edited by Redeasysport; Aug 1, 2008 at 11:56 PM.
Pro
Joined: Jun 2008
Posts: 610
Likes: 1
I'm going to jump in here and suggest that the relay may be actually closing but there is insufficient current being delivered to the a/c clutch. It is possible that you have a loose terminal(s) in the relay socket. When you bypass the relay with a jumper you make a solid connection and the clutch works.
To test if the relay is being activated have someone help you while you hold the relay to feel it it "clicks".
To test if the relay is being activated have someone help you while you hold the relay to feel it it "clicks".
Thread Starter
Intermediate
Joined: Jun 2008
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What I don't get is what the PCM is doing here it seems to be feeding 12V back to the coil when the AC is on because there should not be voltage on the Drk Grn/ Wht wire as the 12V should be dropped across the coil as it is the only resistor in the circuit.Try measuring pnk to drk grn/wht with the AC on and off. That will show the coil energized or not.
Thanks for you help guys but I am going to drop it off and see if someone else can look at it.
Sometimes it takes a second set of eyes