: 1978 Deville BLOWER RELAY---keeps blowing out every 3 months



pompste
05-29-10, 05:14 PM
My BLOWER RELAY blew out again today,just 3 months after putting in a new one.It`s located on far left under dash.It looks as if the previous owner had the same problem and had the circuit professionally re-wired so it`s more accessible to replace.
I was cruising along with AC on and then the fan shut off after hearing a "click sound" from the relay---i pulled over and when i touched the relay it was soooo hot to the touch i had to let go of it.
When i replaced the original blower relay--it had a thick black insulating tape wrapped around it----why i don`t know.

Is this a common problem for these vintage Caddy`s? If so--is there a solution to it? I don`t like the idea of having to replace the blower relay every 3 months or so at $12 each time.

Thanks for any info.

Bro-Ham
05-29-10, 05:25 PM
Par for the course my friend. 77-79's just have this problem. Keep a supply of relays. It's good that the relay was relocated to keep the fuse panel from melting (further?). I've replaced two of these relays in the last year and I live in FL where the AC is going all the time. Replacing a $10 relay every few months is a whole lot better and cheaper than the problems most cars encounter... :)

pompste
05-29-10, 06:01 PM
Par for the course my friend. 77-79's just have this problem. Keep a supply of relays. It's good that the relay was relocated to keep the fuse panel from melting (further?). I've replaced two of these relays in the last year and I live in FL where the AC is going all the time. Replacing a $10 relay every few months is a whole lot better and cheaper than the problems most cars encounter... :)

It is a good thing the relay was relocated-----there are melt/scorch marks on the fuse panel where the relay originally WAS.Now the relay is located about 6 inches away from the fuse panel,completely separate from it.
I`d like to know why it keeps blowing out in the first place----apparently this is a commom problem.I`d also like to know why the relay was wrapped with a thick black insulating tape----it seems to me as hot as it gets,the thick tape would actually make it even hotter and not allow it to cool.

Bro-Ham
05-29-10, 06:19 PM
Oh some of the unanswerable questions of our lives... :) :) :) It's just the way these cars are. The fix is to separate the relay from the panel and pray you don't forget a spare on a sizzling hot day. :)

drmenard
05-29-10, 07:15 PM
If the relay runs the blower motor, have you chaned the blower motor? When these motors get old the can draw alot more current than they should.. And if you do change it , don't look for the cheapest one you can find...

pompste
05-29-10, 07:33 PM
If the relay runs the blower motor, have you chaned the blower motor? When these motors get old the can draw alot more current than they should.. And if you do change it , don't look for the cheapest one you can find...

I would imagine after 32 years,the blower motor and housing is probably loaded with dirt--which may cause the motor to work harder and draw more amps.IF getting at the motor is easy,i might take a look in there and clean things out first and see if extends the life of the relay.
Then again---it seems this is a common problem with this vintage of Caddy`s----and a design flaw.
If i ever replace the blower motor--i will get a good one--preferrably AC/DELCO.

I ordered a new blower relay from AUTOZONE today----because of the holiday weekend i won`t see it until TUES OR WED,i`ll have to drive around with some windows open---whick i don`t like doing.

pompste
05-29-10, 10:11 PM
I actually got brave and removed/inspected the blower motor tonight----it looked amazingly clean and spun freely by hand----when i spun it by hand it made a few rotations before stopping on it`s own.
There was a rather strong rubber like sealant between the base of the motor and the housing it rests on.Breaking that bond was tough.

77CDV
05-29-10, 10:40 PM
It's just a design flaw. These relays overheat just because. The ideal solution would be to find a way to route some of the air flow from the AC to blow over the relay and cool it.

MudAnt
05-30-10, 12:55 AM
There was a rather strong rubber like sealant between the base of the motor and the housing it rests on.Breaking that bond was tough.

I hope you re-sealed the motor to the housing, the under-hood HVAC assembly is meant to be air/watertight.

pompste
05-30-10, 02:10 PM
I hope you re-sealed the motor to the housing, the under-hood HVAC assembly is meant to be air/watertight.

It`s got a good seal on it.I might drop in a new motor and impeller anyway.The impeller on this motor is really thick and somewhat weighty---might be causing it to draw more amps to run.The new motor from AUTOZONE has a lighter weight impeller.

Bro-Ham
05-30-10, 02:21 PM
lighter weight = cheap? Remember, these 1970's Cadillacs were among the last of the overbuilt Cadillacs that weren't built with too much concern for saving money or saving weight. Your car's old original bulletproof components may very well last longer than you do. A brand new lightweight blower motor replacement may last slightly longer than the relays you're so worried about needing to replace every so often using your original old school blower motor. Just a thought before you go down that road. :)

pompste
05-31-10, 12:55 AM
lighter weight = cheap? Remember, these 1970's Cadillacs were among the last of the overbuilt Cadillacs that weren't built with too much concern for saving money or saving weight. Your car's old original bulletproof components may very well last longer than you do. A brand new lightweight blower motor replacement may last slightly longer than the relays you're so worried about needing to replace every so often using your original old school blower motor. Just a thought before you go down that road. :)

I do agree with you when you say these vintage Caddy`s were the last of the "overbuilt" ones.
When i look at my BIIIIIIIIIIIG '78 Deville and a new alphabet soup DTS/DHS pulls up next to me at a light----i`m amazed at what the boat Caddy`s from the past have evolved into-----shrunken down rides that don`t have the class,quality and elegant lines anymore.
When i had the blower motor out yesterday---it did NOT look original---it read SIEMENS on it and made in china.I`ll ty the new out,when it comes in next week, and see if it makes any difference,it has a lifetime warranty, with the relay.I`m going to keep the motor i have----at best i`ll have a backup blower motor in case one quits on me----and i like working on my ride----it keeps my mind focused on other things since my mom died a few months ago.

77CDV
05-31-10, 04:58 PM
Sorry to hear of you mother's passing. Hope your new blower motor does the trick.

pompste
05-31-10, 11:32 PM
Sorry to hear of you mother's passing. Hope your new blower motor does the trick.

Thank you much for your condolences! We all only get 1 real mom in life and when she`s gone forever---it leaves a void,a big one.

You`re right when you said "route some of the AC air over the relay to COOL it"---that would help.

pompste
06-05-10, 06:32 PM
I put in a new relay from AUTOZONE and it worked great for 3 days-----today it only blows the fan in LOW speed only.The low speed on this ride is like a barely noticeable air flow.
I don`t know if i`m getting cheaply built relays or what.I paid $9.99 for the last one---i got this new one for free since the first went out within the warranty period.
They offer another relay there made by EVERCO for $13.99.---maybe i should try one of those.
Any suggestions will be appreciated.

deVille33
06-05-10, 08:39 PM
One other thing you may want to check out may be the connectors at the Resistors and the wire to the ground plug. If you find the wire ends to the spade connectors are green in color, you have resistance to your motor operation. If your relay connector is hot, the wire going to the motor has to be hot also. Check this wire for resistance. This circuit draws 30 Amps so it will operate through the resistance of the corrosion at the wire ends, but will run hot until it burns out the relay.
You may find corrosion at the relay connnection and that could be why there was so much tape wrapped around it. Possibly keep it from corroding again. Check the wire, if it has corrosion , to determine how far down the wire the corrosion goes. You may want to concider replacing the complete blower motor harness.

csbuckn
06-05-10, 08:43 PM
maybe you could run a smaller fuse. Or put a smaller inline fuse on that relay

77CDV
06-05-10, 10:17 PM
Sounds like connections problems to me.

pompste
06-05-10, 10:25 PM
One other thing you may want to check out may be the connectors at the Resistors and the wire to the ground plug. If you find the wire ends to the spade connectors are green in color, you have resistance to your motor operation. If your relay connector is hot, the wire going to the motor has to be hot also. Check this wire for resistance. This circuit draws 30 Amps so it will operate through the resistance of the corrosion at the wire ends, but will run hot until it burns out the relay.
You may find corrosion at the relay connnection and that could be why there was so much tape wrapped around it. Possibly keep it from corroding again. Check the wire, if it has corrosion , to determine how far down the wire the corrosion goes. You may want to concider replacing the complete blower motor harness.

Thanks for the info! The thick black insulation tape was wrapped around the blower RELAY itself only,the part i keep replacing.I still don`t understand why it was there in the first place when i replaced the first relay because the tape would actually RETAIN the heat the relay makes instead of allowing the heat to dissipate without the tape.
The relay has been professionally re-wired so it`s not in it`s receptacle anymore---it`s now about 6 inches away from it`s receptacle---making it easier to replace.There were scorch marks on the receptacle-----probably why it was re-wired.I bought this ride just 4 months ago.
I ordered the EVERCO relay tonight--should be in by tuesday.At least i`ve got low fan speed,for now.Hopefully the EVERCO new blower fan i just put in will sync up with the everco relay.
I`ve had a good look at the wiring several times---i don`t see any corrosion at all and the wires don`t get hot even though the relay itself gets really hot when the fan did run on high.

deVille33
06-06-10, 10:16 AM
Okay, assuming all your connectors are corrosion free, check the continuity of the heavy wire, which should be your direct circuit wire. It should have little resistance. Pull out the resistor block in your heater / AC module and ensure nothing in there has been comprimised. You can also check the resistance in the coils. I don't have know the figures and I don't have my SM here, but there is conciderable info in the SM on how the system works and the variables in operating voltage values. You can put a ammeter across the connectors of the relay to find the draw amperage of the motor. It could be your motor causing your overheating. I believe the circuit has a 30 amp limit. If your drawing more than that your exceeding the operating limit.
Your relay operates very much on the same principal as that of a voltage regulator. As the sensor built into your climate control determines the cabin temperature, a different circuit to the relay is activated causing a set of points to open / close and change fan speed. High speed use is the same as a direct wire circuit. If your circuit draw is excessive, your relay is the weak link, and like a fuse it will burn out.
Open one of your blown relays and study it. You may find that the points have fused and the strap has burned through.

pompste
06-07-10, 03:05 AM
Okay, assuming all your connectors are corrosion free, check the continuity of the heavy wire, which should be your direct circuit wire. It should have little resistance. Pull out the resistor block in your heater / AC module and ensure nothing in there has been comprimised. You can also check the resistance in the coils. I don't have know the figures and I don't have my SM here, but there is conciderable info in the SM on how the system works and the variables in operating voltage values. You can put a ammeter across the connectors of the relay to find the draw amperage of the motor. It could be your motor causing your overheating. I believe the circuit has a 30 amp limit. If your drawing more than that your exceeding the operating limit.
Your relay operates very much on the same principal as that of a voltage regulator. As the sensor built into your climate control determines the cabin temperature, a different circuit to the relay is activated causing a set of points to open / close and change fan speed. High speed use is the same as a direct wire circuit. If your circuit draw is excessive, your relay is the weak link, and like a fuse it will burn out.
Open one of your blown relays and study it. You may find that the points have fused and the strap has burned through.

Thanks for the info------what you suggest sounds a bit more complex than my current knowledge will allow me to do.
I do actually hear the relay "click" when the climate control senses a temp change and changes the fan speed when set on "auto".
I wish it had a permanent "medium" fan setting----it just has "low--auto--high".I know the relays on these models would last longer with a "medium" setting.
I just put in a brand new blower motor last week--so i don`t think that it`s causing the problem.

pompste
06-07-10, 03:09 AM
maybe you could run a smaller fuse. Or put a smaller inline fuse on that relay

A smaller fuse would just blow before the relay is overloaded---right or not? If so---then i would be replacing fuses instead of relays---and that does`nt make much sense.

deVille33
06-07-10, 08:47 AM
I do actually hear the relay "click" when the climate control senses a temp change and changes the fan speed when set on "auto".
I wish it had a permanent "medium" fan setting----it just has "low--auto--high".I know the relays on these models would last longer with a "medium" setting.



When this system is working properly, it's an engineering marvel. I too wish it had a manual override. All sectors of the system have to function properly in order for the controls to operate as they should. Low pressure in the AC side factors in how the heat control works, because the air entering the air box is heated at the heater core, then passed through the AC coils to obtain the desired tempurature of the cabin.

Brother_B
06-08-10, 09:24 PM
Isn't it the other way around? Air is cooled first (to dehumidify) and then heated back up?

deVille33
06-09-10, 08:48 AM
It's one or the other. I haven't checked any of this out with the SM as I have other things more pressing going on. My input is based on what I recall from the last time I had the SM out to study this system. At the present I'm involved with getting my rechromed rear bumper reassembled and gathering info on that from the SM and the Fisher Body Manual. It's all details, details, details.

77CDV
06-09-10, 02:14 PM
Isn't it the other way around? Air is cooled first (to dehumidify) and then heated back up?

You are correct, sir.

pompste
06-10-10, 06:28 PM
MOST RECENT UPDATE:

Seems it may NOT be the blower relay that is the problem now.I installed the newest relay today---and it to,like the previous new one,only works at LOW speed only.No matter what position i slide the slider to----it`s always on low speed.
The very first original relay that blew out---would not work at any fan speed.The 2 newest ones i put in only work at low speed.I`d be content with low speed only,but it really does`nt blow much air on low.In the winter,i`d be freezing--and on really hot,humid days---low speed AC air is not enough.
Just to be sure it`s not the new blower motor i put in last week,i connected the old blower motor,which worked at all speeds,by just connecting the ground wire to it along with the other connection,and it too would only run at low speed with either of the 2 newest relays.
So,i`m stumped again.
I`d appreciate any suggestions to solve this mystery.
Thanks much!

77CDV
06-11-10, 01:39 AM
http://www.cadillacforums.com/forums/rwd-19xx-1984-deville-fleetwood-1985/202181-1975-eldorado-hvac-blower-motor-speed.html

coupiedeville
09-27-10, 10:05 AM
I had this blower relay issue for many years on my 1980 Coupe deVille. It was a concern of mine because both the relay and the connector would show the starting signs of melting and I feared sooner or later a dash fire would be the result.

I recently found that GM issued a Technical Service Bulletin (TSB) on this back in 1985. The TSB states the fix is to rewire the old 4 prong relay to a different 5 prong relay (although only 4 of the 5 prongs are used on most of the deVilles). The TSB repair kit part number has changed many times, but the latest part number for the kit is 12167112. It retails for $91.92, but a google search on the part number will give you sources who will sell it for about $60.00. Once I changed this (I made sure to solder all of the connections instead of using solderless connectors provided in the kit), the blower has worked flawlessly ever since.

If it has been rewired and you are experiencing the relay failure, then the problem is likely a tired motor. Probably best to check the draw at the motor.

Bro-Ham
09-27-10, 02:28 PM
Thanks for posting this. :)