: Blower Relay keeps melting



ferrisworld
03-30-05, 01:52 AM
My blower motor relay in my 1979 Sedan Deville keeps melting. It's getting expensive since I've had to replace it 3 times now, and they're about $20. I've tried a lot of things to fix the problem, including a new programmer, and a new blower motor. My control head is also only about 2 years old. Vacuum seems fine, I had the blower resistors tested, and they look fine too. I'm afraid to put my new relay that I just got in unless I rig up a circuit breaker inline.

Katshot
03-30-05, 05:41 AM
Had the same problems. I tried mounting the relay IN the A/C duct to cool it and even THAT didn't provide a permanent fix. In the end, I decided to use a better relay.

ferrisworld
03-30-05, 05:47 AM
Well, I'm assuming thats on your 95. The older ones have a completely different system I think, and I doubt it has anything to do with the quality of the relay if the original one thats 25 years old suddenly just went out and so do all the new ones I've put it.

Katshot
03-30-05, 07:02 AM
Not my '95. I was talking about the old cars, like late 70's as I recall.

The Ape Man
03-30-05, 09:21 AM
I just went through the same thing with my '80 last spring. I finally decided to use a pair of those little Bosch black cube relays in parallel. The Bosch relays use spade terminals. I made some jumpers using heavy duty male and female solder type spade terminals. The whole thing now plugs into the unmolested fuse panel. If you see any signs of previous overheating of the relay socket then it might be a good idea to eliminate the terminals which have cooked by soldering to a new pigtail and heat shrinking the splice. Crimps will not work here. The coil wiring can be done with light gauge wire. Works better than stock. Very little Voltage drop to the blower. The Bosch relays run cool. You can probably get a better relay from Grainger but it will not be a plug-in deal.
BTW, another failure of some of those relays is the coil cooks itself and the turns become shorted. That allows tons of current to flow through switches including the block temp switch.

ferrisworld
03-30-05, 12:57 PM
Well, so, if it is the relays, and they're defective like you guys are saying, shouldn't someone tell the people that make them so they can make them better? And shouldn't I be able to get my money back after buying 2 of them and having them blow out 2 weeks later?

The Ape Man
03-30-05, 09:30 PM
Well, so, if it is the relays, and they're defective like you guys are saying, shouldn't someone tell the people that make them so they can make them better? And shouldn't I be able to get my money back after buying 2 of them and having them blow out 2 weeks later?

You are probably correct but don't hold your breath. First of all, the relays were marginal as designed. You may have a later alternator which makes 1/2-1 full Volt more under load. Combine the 2 and you are over the edge. Let's say your original blower was AFU and drew too much current. Well the replacement might also draw more current than the original too but for another reason. That replacement will often be one which has to fit many models and could very well have a different current spec. There are a lot of variables here. The guy behind the parts counter probably will have no idea about any of this unless he is working his way through engineering school. Your relay design is obsolete so nobody is going to turn a profit spending any time on it. My repair advice to you is what I used on my own car which had 41,000 miles at the time and had the original factory relay. Some original equipment electronics just plain don't hold up. This era of Cadillacs was notorious for climate control in-op blower problems. The plug in the rear of the control head melted on many a '79. If you want to drive and maintain a car like this then sometimes it's just better to make a few changes.
If you do find an engineer interested in the project then have him design a pulse width controller. The '81 and later Cadillac blower power modules didn't hold up all the time either. Those wasted so much energy in heat that they had to have a heat sink sticking into the air duct.

ferrisworld
03-30-05, 09:42 PM
Hmmm, well, do you know how many amps it should be pulling to be safe? I could stick my multimeter on there and see how many amps the blower pulls. The alternator on the car is the one that came with it when I bought it, and I've had it for 3 years now, so I don't know if that would be the cause. One thing I've done is the power antenna cable broke, and, not knowing where to find a new OEM one, I bought one from the auto parts store. It has it's own relay built in so I took out the stock relay, bridge the connections, and it worked great for a while but then a fuse blew. I suppose I'll need to put a stronger fuse in for the newer antenna, but I'm wondering if maybe that is having an effect on the AC system. I'm not really sure though because after the fuse blew for the antenna I just left it for a while so the antenna wasn't getting any power the last couple of times the blower relay melted.

The Ape Man
03-30-05, 10:28 PM
You will probably not be able to make use of your multimeter. Most only handle 10 amps. Your blower motor probably draws more than that. No, I don't know exactly how much. This has nothing to do with your power ant. Don't increase fuse size. The wiring on small fuse curcuits is almost always lighter gauge. Copper cost a lot of money.

ferrisworld
03-30-05, 11:35 PM
well so if I can't test how many amps the motor pulls then how do I know if thats the problem or if it's something else?

The Ape Man
03-31-05, 10:48 AM
You can go out and buy a clamp on ammeter probe which will plug into many DVM's and allow you to measure all the way to 600 Amperes. You can also replace your relay with a heavier design and forget the rest......

ferrisworld
03-31-05, 10:14 PM
Well, I went out and I ordered this other relay thats rated at 40 amps, and some dudes told me that the fans should only draw 20-25, so it should be good. I hope this works and doesn't cause other problems like the connector on my head unit melting like you said happened on some cars.

ferrisworld
04-04-05, 01:00 AM
Okay well the new type of relay is in and it's all good so far. Now I've got a vacuum leak somewhere because the actuator door for the top vents isn't opening. I can hear air hissing from somewhere too when I put it in any mode where it should open.