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Old 11-08-2009, 11:21 PM   #1
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Question Removing and testing a relay

Simple question this time.

In response to Danthurs' excellent write-up on how to change a blower motor, he recommends checking the maxifuse and relay first. The former was not an issue, but for the life of me, I can't figure out how to remove a relay, much less test one.
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Old 11-08-2009, 11:25 PM   #2
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Here'* how to test. https://www.gmforum.com/t279561/

Getting them out is a bit of a pain. You need to pull it out. The relay is inside a box that slides on a rail on the bottom of that box.
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Old 11-09-2009, 12:30 AM   #3
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Thanks, Dan; I must have missed that.

Last edited by SignOfZeta; 11-09-2009 at 01:31 AM. Reason: Got bored. Tested anyway.
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Old 11-09-2009, 01:29 AM   #4
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Default Testing an open relay (e.g., blower motor relay)

Duplicate post; keep reading.
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Removing and testing a relay-img_0079.jpg   Removing and testing a relay-img_0076.jpg  

Last edited by SignOfZeta; 11-09-2009 at 01:30 AM. Reason: Posted twice. My bad.
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Old 11-09-2009, 01:30 AM   #5
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Default Testing an open relay (e.g., blower motor relay)

I tested the relay for the blower motor (the one you're holding in the writeup). This one, unlike in the aforementioned relay test write-up, is a four-pin relay that is normally open. It'* also in a little plastic case to make installation easy, deinstallation tricky (there'* a tab on the top), and testing a bit of a pain, unless you have four hands. (I do not.)
Attachment 1616

First, if you peer inside, there are numbers next to the pins. Now take a look at the schematic on the top of the relay. It will look like the one in Danthurs' writeup, but different. You can see the control circuit on pins 85 and 86, diodeless, and the current flows through pins 30 and 87:
Attachment 1615
  • Set your voltmeter to 200Ω, and touch pins 30 and 87. This relay should show infinity, as it is open when the control circuit is low.
  • Take a fresh 9V battery, and wire it up to pins 85 and 86. (As it'* diodeless, you can hook it up in either direction. I did, just to make sure.) You should hear a click. Now, if pins 30 and 87 read close to 0Ω, your relay is good. Put it back in the car.

Guess I'm replacing the blower motor. I know I'm not going another New England winter without a defroster. Scraping ice off of the inside of my windshield is not how I'd like to spend the next four months.
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Old 11-09-2009, 08:20 AM   #6
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Colin... that diagnosis sounds familiar. When we tested your blower motor connector and saw 12V+ on all blower speeds, that was essentially the same test. The only one we didn't do was check for the correct amperage at the connector.
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Old 11-09-2009, 08:21 AM   #7
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Did you try hooking power to the motor to see if it spins?
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Old 11-09-2009, 09:03 AM   #8
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I've found that can be a misleading test in some cases. If you use say a battery charger, you can end up putting more amps to it and getting the motor to work. Yet in the car it fails to work.
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Old 11-09-2009, 09:09 AM   #9
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I hooked up a volt meter to the plug and moved the fan control up and down while watching the voltage.
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