Continuously running blower

[cpykt]

I have an older central heating system that the blower continuously runs. I have changed the blower limit switch that didn't fix the problem. The thermostat seems to be working fine but no matter where I switch the fan to (aauto/on) it keeps running. I noticed what seems to be what looks like a relay where all the wiring comes together and wondered if this might be the culprit. I work on electronics in my employment but I'm not an hvac person so I'm hoping someone can help me out.

[Java_Bob]

could be the fan relay, see if there is 24 volts to the coil if so look at the stat again.

[HayZee518]

the thermostat is just a control device. it controls relays and contactors to operate the blowers, compressors etc. a regular old fashined honeywell thermostat is just a normally open switch. modern day thermostats are programable switches. control voltages are 24 volts in most cases. look at the diagram of the thermostat. it should be able to tell you what is connected AT WHICH SWITCHING MODE.