andrew-theasby
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| posted on 10/3/08 at 08:55 PM |
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should relays get hot?
As title really, i have a 306 hdi which, about 6 months ago, i smelt burning as i pulled into work. After investigating, i found the relay for the
heater had melted on one side and stuck itself to the board. Managed to get it out but had to put another in to see what the problem was. When i did
everything worked fine, but the relay got warm, so i unoplugged it. Left it unplugged for ages till i got chance for a better look. This one relay
knocks out the air con, heater/cooler control, and also the fan speed (how does that work, its only one switch on its diagram???) Anyway, had to plug
it back in one night cause i was in a storm and couldnt clear my window. After a while of blower on full, it wouldnt switch off or slow down, so
unplugged it again. Assuming the relay had jammed i got home and plugged it back in again to see and everything worked fine, but nothing i did seemed
to make it click so left it unplugged for another few weeks. Just plugged it back in again to start looking at it, and with the blower switched off
for my 2 x half hour journeys, the hot cold control worked fine, and a/c light came on but i switched it off so all seems fine but the relay got warm
straight away and stayed warm, but ive also noticed the same green relay thats next to it for elec windows also gets warm. None of the others do, but
im worried its all going to catch fire after the first melted. Is this normal and the problems are just a coincedence, or is something causing a
fault or two? Can anyone advise please?
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r1_pete
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| posted on 10/3/08 at 09:00 PM |
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relays shouldn't get that hot, is there any sign of arcing on the connections? The current round the actuator coil is very low, and
shouldn't be enough to cause that amount of heat without blowing a fuse, so I'd suspect the problem is on the high current
'switched' circuit.
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andrew-theasby
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| posted on 10/3/08 at 09:47 PM |
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No, wouldnt really say there was any sign of arcing. The terminal where it melted is on the heavy circuit. What would cause it to draw extra current
when the fan is off? Could something be slightly jamming the hot/cold air valve??? That must be in some way electrical (not like a slider on most
cars) as it wont change from hot to cold without the relay in, but it does work fine when its in.
 
Rescued attachment relay2.JPG
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PaulBuz
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| posted on 10/3/08 at 10:11 PM |
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fit a new relay & carry out a load test with a meter if you can.
Obviously the current should be less than the relays rated current (20 or 30 A?)
The problem may just be a faulty old relay.
Once a bad connection forms within the relay, you create a hotspot which will only get worse & eventually burn out the relay.
ATB
Paul
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andrew-theasby
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| posted on 10/3/08 at 10:18 PM |
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That picture is of the first relay that melted. Since then i have been using a new relay, but the old one does actually still work. The one that was
in when the blower jammed on full was the new one. What current should be going through it when the blower is off? Without it, nothing works. At
first i assumed the relay would just be to switch the blower on and off, but obviousy it isnt. And the one next to it gets warm too. I will try and
measure it tho
Just thought, not sure well have a DC ameter that will carry that kind of load, so probably cant do that 
[Edited on 10/3/08 by andrew-theasby]
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omega 24 v6
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| posted on 10/3/08 at 10:33 PM |
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Looks like a possible bad/poor connection INSIDE the relay.Possibly a dry solder joint or a damaged/broken track.
Also it looks like an ign controlled relay (unless it's a trick of the camers then the power circuit terminal look to be bigger than the std
6.5mm ones. So it could in theory be rated to as much as 100amps.
[Edited on 10/3/08 by omega 24 v6]
If it looks wrong it probably is wrong.
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andrew-theasby
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| posted on 10/3/08 at 10:48 PM |
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Its rated 25 amps, just the same as the one next to it, just a standard 4x 6.5mm pin relay. The old one got really hot, the new one gets hot, and the
one next to it gets hot. Wouldnt that point to something other than a faulty relay? (Dont know what btw, just thinking out loud)
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omega 24 v6
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| posted on 10/3/08 at 11:05 PM |
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The relays WILL get hot to an extent. Don't know in degrees I'm afraid sorry. You could try a lazer thermometer at it though if your
really worried. I'd imagine not more or round about 40 th 50 degrees C. You should be able to touch/hold it without burning yourself. Also if
the relay is fused and the fuse is of the correct raing and does not blow then I'd suspect the first(burnt) relay to be fubbared.
If it looks wrong it probably is wrong.
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andrew-theasby
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| posted on 10/3/08 at 11:41 PM |
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Thats pretty much what i thought, until the fan stuck on with the new relay in. Cant explain that one. You can still have a fire with less than
20amps. They are definitely hot rather than warm, but theres no others of that size to compare with, none of the others get warm at all. Ill try
running the blower a bit tomorrow and see if it gets any warmer, and progresively try more. Until then im carrying a fire extinguisher  Thanks
[Edited on 10/3/08 by andrew-theasby]
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dhutch
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| posted on 10/3/08 at 11:45 PM |
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Interesting.
- I spend two hours the weekend before last chisaling the remains of the rearheatedscreen relay of my new 306 off the holder.
- Ive never had any problems with the prevous 306 in the 7 years we had that, and since i replaced the relay (with a second hand one, from said
pervous 306) ive had no problems.
Deffonatly sounds like dodgy relay to me.
- They do get warm if there on a long time, but it should only be warm, burning is always a bad thing in electrical parts imo.
Daniel
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MikeRJ
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| posted on 10/3/08 at 11:55 PM |
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Every melted relay or fuse I have ever seen (mostly on French cars) has been caused by a poor connection between the high current wiring and the
relay, often the crimp on the connector is the culprit. This can put a lot of heat through the affected terminal into the relay.
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RazMan
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| posted on 11/3/08 at 11:32 AM |
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I had a similar experience with a fuse box which had a very slightly loose fitting fuse on a headlamp circuit - the small resistance caused some heat
which actually melted the fuse box
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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andrew-theasby
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| posted on 11/3/08 at 12:19 PM |
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Thanks, that sounds like whats happening then, maybe the other one is about to do the same too 
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