View Full Version : Trane MAU tripping on Return firestat
01-29-2010, 01:12 PM
Two year Trane MAU Model GRCA30GF trips on Return firestat that is set at 130F. Reset unit numerous times until I noticed the blower fan not coming on. Jumped out HL-1/SL-1 and fan came on. Replaced HL-1/SL-1 snap switch unit ran for two weeks now tripping out again on firestat. Is it possible for the firestat located on the return to trip at 130f when located so far away from the fire box on a ten degree day. Even if the fan time delay failed and the blower didnt come on wouldnt the safety limit (SL-1) trip first.
01-29-2010, 01:27 PM
Change your sensor first to eliminate any possible moisture in the sensor causing it to trip., make sure your filters are clean .., then move to all else..
01-29-2010, 02:17 PM
If the unit is configured for intermittent fan, the fan is supposed to start 60 seconds after the main burners light. The fan is supposed to stop 120 seconds after the call for heat is satisfied.
If airflow is low the two minute cooldown might not be long enough.
If unit is overfired the one minute fan delay on may be too long and the two minute cooldown may not be long enough.
Check manifold pressure, temperature rise, fan timing, and high limit safety switch wiring.
01-29-2010, 04:12 PM
I would like to rule out the honeywell firestat/highlimit also. I could put some controlled heat on it and see what temp. it trips at. I just have never seen one fail at only two seasons. Will also check on the other advise giving. thanks guys.
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