Electrical Relay Problem! Melted!

jmamrak

Registered Member
Original poster
Jul 17, 2014
380
Lagrange KY
I have an air and train horn system in my truck. The compressor is mounted in the rear topper. The viair unit is controlled via an electronic relay and that is controlled by a pressure switch on the control side. The control side is fused for 5 amps and the load side is fused for 40 amps both inline. Today the compressor did not kick in as usual. I checked the fuses (both good) and the relay. I found a melted connector on the relay. I did some research that said an overload or an overvoltage could be the cause. Well the compressor works fine, the pressure switch works fine, and the fuses are both fine. It was also a 40 amp rated relay. The compressor I believe draws around 30 amps. I am not sure what happened. When I removed the fuse and reinstalled I could hear the relay half clicking. I installed an american made relay and threw away the one I had from China. Any suggestions?
 

Sparky_911

Member
Gold Donor
May 15, 2013
2,287
Central Illinois
I had a visit 20000 and never had any issues. Maybe the relay was bad to begin with? Luckily it didnt melt the truck too....
 

jmamrak

Registered Member
Original poster
Jul 17, 2014
380
Lagrange KY
@Sparky_911 Yea agreed! The pin that was melted was the 87 load side output to the compressor. The relay was defiantly an el cheapo. I replaced it with a relay off of a late 1990’s ford vehicle. I make a habit of grabbing the older ford OEM relays when at the junkyard. They always seem to outlast the vehicle. High quality and free! Double whammy!
 
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NPS Ranger

Veteran Member
May 21, 2010
1,932
Penn's Woods
If the compressor running amperage is 30 amps, it may well have a starting amperage in excess of that. Also, with engine running the system voltage is likely 13-15 volts but with ignition on and engine off, it's just battery voltage and the starting load of the compressor will likely drop that even lower, thus raising the amperage through the relay even more. The 40 amp fuse may be a slow-blow type so it survived, but you may want to use a higher rated relay such as 50 or 60 amps.
 
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