My blower quit working little by little. No 1 & 2 speeds, now no speeds. Replaced the resistor, no change. Am looking at the relay next. So the one in the vehicle is an OMRON 12177233. The terminals across the top are: 85-87-87a. Across the bottom they are: 86-30. The OMRON 12177233 replacement I have found has this configuration: 85-87a-87. On the bottom they are: the same as the other 86-30.

My question is: Is there a difference between the two and will the 85-87a-87 configure work the same?

I can get a GM with the correct sequence but at 3x the price.

Thanks again for all the help put out here...

2001 Blazer ZR2
3 button xfer case

 

Dang, that pattern of failure really sounds like resistor. Can you check it out?

 

Here is a scan from my 99 service manual for the manual HVAC fan control. According to this, the configuration of the pins 87 and 87A matter. This is not always the case for relay circuits, but here it looks to matter.

 

It does matter but there are two variables at play. 30 has to be 30. 85/86 can be reversed. With 87 and 87a what matters is that the correct terminal is connected to 30 when energized. The most common refernce is that 87 is connected to 30 when energized but I have seen the graphics on the side of the relay suggest the opposite. If the 87/87a labels are then also reversed then a double negative would make a positive. Unfortunately GM does not consistently show us the connections on the electrical diagrams and the pin locations on the relay socket. And of course if the headlights are not working the relay now in the socket may be a bad cross. I am helping another member where the diagram calls for a 5 pin, the socket is a 5 pin and the cuurent relay is a 4 pin which will not work right. If it were me I would buy the best cross from Rock Auto for under $10 but then test it when I got it, I can help you with that.

George

 

George, I saw your lengthy troubleshooting thread with another member for the HVAC system. Can you give me a direct link please as I can't seem to find it.

I put in a new resistor. No change. New relay. No change. New dash selector. No change. Power to the dash selector. Power to the dash fuse. Power to the under hood fuse. Power to the relay. Power to the resistor harness. But no fan.

I don't want to start jumping hot wires to the fan harness for fear of frying something so hoping your diagnostic thread can walk me through this. Just seems funny that the fan would be the culprit after having the speeds go out in groups of 2. Thanks.....

 

pull the blower motor relay and probe socket 87 and then socket 87A with a voltmeter with black lead to ground and see which one has a constant 12 V. Once you’ve established which one of those pins has always on 12 V then move your volt meter red probe over to the other pin socket and tell me what kind of voltage readings you get with the ignition on moving the blower motor fan selector through the first three positions on the dash?

then while leaving the black meter probe on ground move over to 85 and 86. Probe those in turn while you’re changing the dash selector between the highest fan speed and the next highest fan speed and tell me what you get on both pins. Ignition is in the on position here as well

George

 

Are you sure it isn’t a bad blower motor or bad connection at blower motor ? Both would cause similar issues also. And are easy to check . Have you measured voltage at the connector at the blower motor to check for voltage there with fan on high ?then check other speeds . All speeds except high go through resistor , relay bypasses resistor for high . Wiggle the connector to check for bad connection . When connection gets loose / corroded it can stop working on 1&2 ( resistor provides lower voltage to motor on lower speeds and a bad connection can keep motor from getting enough voltage to run ) and as it gets worse all speeds quit. Very similar to resistor bad . Eventually the low voltage caused by bad connection can burn up motor too .

 

My relay configuration which matched the one I removed.
85=constant voltage no ignition
87a=voltage with ignition
87=4.4mv all selector positions w/ign
86=12v in position 4 w/ign
30=5mv all selector positions w/ign

 

Working with George to try and trouble shoot this but the connector looks clean...

 

I need the actual voltage levels on all of your readings. Also make up a fused jumper and with the relay removed apply 12v from the battery positive to relay socket 30 and tell me if the blower comes on at full speed.

George