The highest fan speed on my '73 Custom Cruiser with the manual air-conditioning stopped working a couple of days ago. The lower three speeds work fine. Following the troubleshooting procedure in the service manual, the problem appears to be a failed "hi-blower cutout relay." I removed this relay from the car, and what it looks like is shown below. I was able to find this relay at rockauto, among other places, and I ordered one (actually two). The part number stamped on both relays is 412687.




I ordered two because there is another relay right next to this one, just as old, with the same part number, and, according to the manual, it is the "hi-blower relay," not to be confused with the "hi-blower cutout relay." Because these relays are all in one location under the hood, if I'm taking one out, might as well take them all out and replace them all at the same time, right?


Anyway, there is a third relay under there labeled "defogger power relay," and photos of it are below. I thought I would replace this one, too, but I can't find one that looks like it. If I search on "rear window defogger relay" or something like that at rockauto or autozone, I get the same relay (or, at least, it looks the same in terms of number and location of the terminals) as the relay above.

This relay has only three pins, and it has nothing stamped on it except "12V" as you can see in one of the photos. Anyone know anything about this relay, such as a part number, another name, or anything else? Thanks.

 

According to the CSM, that relay had three terminals: 1, H, and B.

1 is the pull-in terminal, and completes the circuit through ground
H and B are the switched terminals.

So it appears that this is a simple SPST relay with grounded pull-in coil.



The Parts Manual lists it as #403651.
OldObsolete has it for $125, and
it's on eBay for $168.

Or you can replace it with a $5 40A "cube" "foglight relay" from the auto parts store and be done with it.

- Eric

 

Thanks! Excellent information. The terminals are actually labeled H, B, S, left to right in that photo, and that's exactly what it says on mine.

I'll probably avoid the high-price NOS or whatever units on ebay. The two other relays I bought were also available on ebay for about $125 each, but at rockauto the modern ones are $8.00 apiece, so guess which one I went with!

Thanks again.

 

The saga with this blower motor problem continues.

Below is the page out of the CSM that shows the troubleshooting procedure for hi-speed blower motor problems.




Note that this diagram indicates four possibilities. With the engine at operating temperature, the selector on VENT, and the fan speed set to the highest position (of four possible speeds), you're supposed to move the rear defogger toggle switch back and forth and observe the behavior.

Well, my situation does not match up with ANY of the four. The three lower blower speeds work fine. With the defogger switch OFF, moving the fan speed switch to the highest position, which should cause it to blow at maximum, actually shuts the blower off. If I move the defogger to ON, the fan comes on at maximum speed.

What's supposed to happen is that, with the fan speed on high, turning the defogger switch to ON causes the fan speed to drop down one notch. This is possibility number 2 on the chart ("Normal Operation.")

My problem does not match up with #1 because my car's blower does not stay on HI regardless of the position of the defogger switch. The blower shuts off when the defogger switch is OFF. My problem does not match #3 because my blower DOES work if the defogger is switched to ON. My problem does not match #4 because with the defogger OFF I get no blower at all, and with the defogger ON, I get maximum blower speed.


So what do you do when your problem does not match any of the possibilities in the troubleshooting diagram? Call 1-800-OLDSMOBILE and ask to speak to tech support? I tried that, but the line's been disconnected.



OK, look down at the lower right where there are two diagrams showing the locations of the relays, with the top one for the full-size cars and the bottom one for the Cutlasses. My situation is the top one.

First, this diagram shows FOUR relays. My car has only three. There is no relay located in the lower left on my car ("Low Range Relay"). Can anyone explain the absence of this relay? It doesn't look like anything was removed at some point. There are no mounting holes, dangling connectors, or anything like that.

I DO have the other three relays, I presume, but none are actually labeled the way they are in the diagram. At least, I have three relays in the positions noted.

Second, if you go through the various troubleshooting trees in the diagram, you see that, one way or the other, for the most part, the end result is either repair a short circuit or replace a relay. The third one does have a branch ending with "replace blower speed switch," so that is a possibility to consider. I don't have a replacement blower speed switch to swap in.

But given that replacing relays is a common solution, I thought I'd go ahead and replace the relays. The top two ("Hi Blower Relay" and "High Blower Cut Out Relay) are actually the same relay, same part number, and available anywhere for about $8.00 each. The ones on my car looked to be original, so I went ahead and replaced both. Of course, the problem was not fixed even though I held out hope that the "High Blower Cut Out Relay" was the culprit.

The "Defogger Power Relay" is a different beast. As I noted early in this thread, this relay has only three pins, has no part number on it, and is not available anywhere that I could find easily. Mr. MDchanic was kind enough to provide an actual part number, but as he noted, anywhere I could find one for sale had them for $150 or so. I didn't want to pay that much as I wasn't sure this was the problem, anyway. If I could find it cheap, sure, I'd buy it and throw it in.


Well, as luck would have it, about a week ago, after doing my periodic google searching on the part number, I turned up a possible vendor in Virginia. Their site said they had it for $19.95. Figuring this is too good to be true, I emailed to verify the part number, price, and availability, and he said they had it for $19.95 plus shipping. It is an NOS piece.

My first thought was to tell him "are you nuts? Don't you realize you could sell this for $150 on ebay?" But I didn't. I called, gave him my payment info, and he shipped it that day. I received it yesterday.

Interestingly, even though the box says the correct part number, it is not 100% identical even though the important parts are. I photographed them side by side, and the photos are below. Note that the new one has only one screw hole for mounting with a bent tab to index with the other screw hole, and, more interestingly, it's actually a mirror image with respect to the side of the relay on which the mounting bracket is located relative to the position of the pins.

But the pins will accept the connectors on the car, so I put it in.

Of course, the problem was not resolved.







So I assume the next step is to replace the blower speed switch. This isn't the easiest thing to do as it entails removing the left side of the dash, and that requires disconnecting all sorts of things. Since I DO have the lower three fan speeds, it's not as though I don't have climate control. I can live without the highest fan speed. If I do ever come across a fan speed switch, I'll get up the gumption to disassemble the dash and put it in.

I assume, of course, that doing so won't fix the problem.

I could also console myself by selling the old relay, which probably still works since the new one didn't fix the problem, for $150 on ebay.

 

Jaunty, something's not connected right, which is why the troubleshooting diagram is of no help.

That's why I HATE these diagrams, which they started printing right around 1973 - They treat you like a monkey who doesn't understand the circuit, instead of explaining the circuit to you, so that you can figure it out. If the problem is outside of the things that they predict can go wrong, you're hosed.

In this case, they compound the problem by not showing a diagram for either the rear defroster or for the high blower cutout circuit.

So, basically, it sounds like all of your relays, AND your speed switch, are functioning properly, but the High Blower Cutout Relay is connected backwards.


Here's a picture of the High Blower Relay and the High Blower Cutout Relay:





In your case, either the White wire from the Defog switch, or the Purple wire from the Defog Relay should be connected to the #4 (standalone) terminal of the Cutout Relay. This will energize the relay when the Defogger is On.

The #1 (bottom-of-the-triangle) terminal on the Cutout Relay should be connected to the Black / Orange wire from the High speed terminal of the Speed Switch, so that power is provided to the relay switch when the Blower is set to High.

The #2 terminal of the Cutout Relay will carry current from the High speed terminal of the Speed Switch when Relay is NOT energized (Defog OFF), and
the #3 terminal of the Cutout Relay will carry current from the High speed terminal of the Speed Switch when Relay IS energized (Defog ON), SO
The #2 terminal needs to be connected to the #4 (standalone) terminal of the High Blower Relay, and
the #3 terminal needs to be connected to the Light Green wire that goes to the Blower Speed Resistor.

I suspect that in your case, the wire that's supposed to be connected to #2 is connected to #3 instead, and the wire that's supposed to be connected to #3 is not connected to anything.






Any questions?

- Eric

 

Thank you for all the info! I'll see what I can do.

But what bothers me is your statement above. The high blower speed WAS working just fine from the day I got the car in January 2010 until the end of July 2014, or almost 4.5 years. Then one morning about a month ago it suddenly doesn't work. I didn't do any fiddling with the wiring, and I found nothing disconnected amongst the various relays. In fact, I don't see how anything can be connected wrong.

The two four-pin relays, as can be seen in your photo, have their pins arranged in a clump of three on one side and single one all by itself on the other side. There is a single, plastic, t-shaped connector for the clump of three and single plastic connector for the all-by-itself pin. So there's no way to connect them wrong or reverse the wiring or anything. I'm sure these connectors were designed this way specifically so they could not be connected incorrectly.


Yes. Goblins?


One possibility that occurs to me is that one of the connectors has gotten dirty. I would think that, with all of the pulling them off and pushing them on I've done in the last few weeks, any dirt might have gotten rubbed off, but maybe not. I will take a closer look at them and also make sure that the wires attaching to their back sides are still solid and intact.

 

I agree: Goblins.

I'd recommend testing all of the relays as per the diagram above, and testing the continuity and function of all connections - I suspect you have enough information now to get it figured out.

Based on what you're saying, I honestly have no freakin' idea what could have gone wrong.

- Eric

 

First, I have not done anything further to resolve my blower motor speed problem. I still have the three lower speeds but not the highest. The highest speed will engage if I turn the rear defogger switch to ON at the same time, a set of circumstances not covered in the troubleshooting section of the chassis service manual. Call me lazy, call me content, but with three out of the four speeds working, I didn't see an urgency about taking the dashboard apart to try to fix whatever's wrong with the blower speed switch, and I don't have a replacement for it yet, anyway.


Well, another problem has cropped up that I think might be related to the newest relay I installed. Remember from earlier posts above that there are three relays in question, two of which are identical and are available anywhere for about $8.00 each while the third of which is not available anywhere except ebay for $150. I did manage to find a supplier in Virginia who had one he was willing to sell for $19.95 plus shipping, so I grabbed it before you can say boo.

As I noted above, putting in first the two easy-to-get relays and then later this third relay, which was not exactly 100% identical to the original but which looked functionally equivalent and had the same part number, did not solve the problem. But I left them all in, particularly this third one, anyway, figuring what harm would it do. Ha ha ha.

One thing I did notice at the time but did not pay any attention to was that, when I reconnected the battery after swapping in the third relay (I always disconnect the battery when doing electrical work), I heard this relay close. When I would then immediately remove the cable from the battery, I heard the relay open. Hooking the cable back up, and the relay closes again. Interesting. At the time, I thought this might have meant my problem was solved because I did not hear this relay open/close sound when the old relay was installed in the car.

But, as I said, the blower motor problem was not solved.

All of this happened at the end of August, and I had been driving the car relatively regularly since then, never having it sit more than two or three days between starts, until this morning. It had been five days since the car was last started, and the battery was totally dead. The dome lights barely glowed at all. I thought "what!?!?"

In almost five years of owning this car, I have never had a problem starting it. The previous owner had put a new battery in, in December 2009, just before he put it up for sale, and I replaced that battery only a month ago (September 10) because it had developed a bad cell. But it was almost five years old and was a cheapie battery, anyway, so I didn't think much of the fact that it was time to replace it.

So what's causing my brand-new battery to drain completely? Of course, there could be a current draw somewhere, but to have that happen after years of no electrical problems and at about the same time as a new battery was put in AND a new relay which makes clicking noises was put in is too much of a coincidence. I figured the likelihood of a new battery being bad is low, but of course not impossible. But I was still nagged by that closing relay.

If a relay closes, that means it's drawing current, right? A relay is basically an electro-magnet that energizes and becomes magnetized when current flows through it to close the switch. As long as the relay is in its magnetized state, it's drawing current, right? So that relay that I hear closing when I attach the battery cable is drawing current all the time, right? That's my assumption.

As I said earlier, and as you can see in the photos below, the two relays are not 100% identical. One difference is the configuration of the mounting bracket, which is nothing, and the other is the arrangement of the pins, which I had originally thought was nothing, also, but which might, in fact, be everything. The two relays are essentially mirror images of each other, at least with regard to the orientation of the T-shaped, two-spade connection, while the third spade lug on the new relay is at right angles (oriented vertically) to the way that lug is oriented on the old relay (horizontally). But it was no problem attaching the connectors.




I'm wondering if the old relay is a "normally off" relay while the new one is a "normally on" relay that should be in a circuit that is only live when the ignition is on. In any event, to test my theory, I put the old relay back in. The new one hadn't solved my problem, anyway, so it wasn't like I was losing anything. As before, I heard no sound of a relay closing when I reattached the battery. So I have my fingers crossed. I have a battery charger and have recharged the battery. The car starts up just fine now. I just need to wait five days and see if the battery dies again or if I can still start the car.