mrm2003

Hello,

I am new to this forum and I have searched the internet for answers without any luck.

When I changed the cabin air filter, I discovered 1 burned relay next to the cabin air filter. I have not discovered any thing that does not work on the car so I do not know what this relay is for. There is total 3 relay in a row any they are marked A002 542 26 19. There is also 2 fuses next to the relay which are 30A and 60A. Can anyone tell me what these 3 relay and 2 fuses are fore?

Anyone how know the answers? (The local dealer did not know)

(on the attached picture there is only 2 of 3 relay showing)

Maj. Dundee

The below illustration is for the fuse/relay box on U.S. models and as you can see relay #7 is not used. What it is used for is not known.

alphonsohall

Possibly the 'optional' cabin booster heater?

Link is for reference......

http://www.justanswer.com/mercedes/4...el-heater.html

mrm2003

Hi, thanks for response.

The fuse/relay box you refare to in the attachment is located at the right side of the passanger side. In my car I also have this fuse box. The 3 relay I refare to is located under the cover for cabin air filter.

mrm2003

I understand from the link that the heater booster dos not have external relays:

"Diagnostics Engineer :
Electrical heater booster must have constant positive supply and 2 communication lines to ECU. The controls are integrated into heating unit- so there are no external relays to check."

mrm2003

Hi,

I have checked more and found the cables are marked:
1 cable attached to fuse holder: #6805-F24/5-2->K16/2-2
1 cable attached to relay holder: #6802-K16/1-8......

Maybe this can help someone to tell me what these relays are used for?

ricksmerc

hi mrm2003, I had the same problem and when I saw your post I investigated these relays. I have one that has one side melted. I assumed this controlled the heater boost due to the thickness of the wires going into this relay to carry the large amount of current for the heater. So I took it apart. Inside there is a spool of copper wire that triggers the solenoid. The smaller pins control the solenoid and the larger pins carry the current to the heater. If you put an ohmmeter on the large connectors and manually push the relays closed then there should be a reading. I did not get a reading! So I cleaned the contacts with some p600 paper, bent the copper contact a little and presto it worked. After reassembly I left the relays dangling and started the car. Immediately I got HEAT from all vents with the engine temp needle pointing to minimum!!

Of course, you could just buy a new relay!! No idea the price. Don't be tempted to swap it for one of the other relays as they all seemed to go on and off as I was changing the temp control knob.

Hope this helps!

ricksmerc

My relays are black, prob due to UK model as its on the left side but the melted appearance looked just like yours

mrm2003

Hi Ricksmerc. Thanks for your reply. I have changed the relay, but I have not discovered any change in equipment in the car. Anyway when you refer to optinal heating booster I can recall that sometimes the heating did not work last winter. Since this heating booster is optinal, can you please let me know where it is located in the car? Maybe a picture off it. My car is orignal imported in 2005 from Germany, I am not sure if heating booster is fitted or not. The relay I changed was probaly damaged due to water/liquid from above. When should I feel heat from the vent after start of the engine it the heating booster i working?
Thanks.

ricksmerc

Hi mrm2003. On my car the heater booster is standard. My car is a 2000 model and if it has this feature then yours must have it as standard. Check your user manual...that's where I discovered that my car had it. If water has got into the electrics then you may have some corrosion on the electrical parts. Sometimes a spray of WD40 helps before replacing the relay. Also the heater booster only kicks in when outside temp is below 8C. Try to start your car with the relays accessible. Keep your hand on the relays and you will feel a click when they are activated. The one you replaced should become warm/hot. Move the temp knob around from red to blue and you will feel the relays clicking, especially when changing from max cold to hot. If this does not work then there may be a bad contact between the thick red wire behind the socket of that relay as your picture shows a lot of heat damage, more than I had. When it works you will feel heat coming out of the vents within a minute (and that relay should be quite warm!)
Hope this helps

mrm2003

Hi ricksmerc,

Once again I found the relay melted.
As fare as I can see there may be 2 resonce for this:
Option 1:
The amp on the relay is too small. I wonder what is the Amp on this relay? Can you please check on your car? MB part no. A 0025422619. There are 2 fuses marked 60A and 30A just below these 3 relay, maybe the 60A fuse have something to do with the booster heater? I think the relay must be 60A aswell.
Option 2:
I can see some residue of liquid from the AC unit. The liquid may have shorted the relay. I have put a waterproof "roof" above the relay to prevent this to happen again.

I need the get a new relay and a relay socket.

mrm2003

why do the relay melt. any suggestions?

Mrm2003

ricksmerc

Hi mrm2003. Sorry to hear about your relay. The relays melt due to too much current going through and the reason for this is a mystery. What I have noticed in my car is that the engine warms up faster as well as producing more heat in the cabin. I am assuming that the heater must heat up the engine water system! This is guess, so don't take it for granted.

When I was listening to the relays as the car warmed up I noticed the other relays were switching on and off. It could be that your other two relays are at fault and are not switching when they should. If you are thinking of changing the relay again, I suggest you keep a finger on it while switching the engine on with the heater dial at max COLD which means that the relay should not switch on. Then turn it until there is a click and the relay should warm up. My relay got warmer than I expected.
Also, the fuses I have are the same as yours... BIG! Never seen car fuses that big.

Sorry I could not be of much help.

Rick

mrm2003

Hi ricksmerc,

I have search the net and found that this standard relay used by MB is 40A. If the current is to high for this relay a will change it to a bigger one. I have also ordered a ny relay socket. I am suprised that MB are using this standard relay all over the car. If you look at the power cord on this 3 relay under the glovbox it is the aft one which have the bigges cord (highest current).

Thanks for your replay.

Regards
M