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Question

Trane xe80 ... 1993 year model ... has a 180 degree limit switch ... yet it cycles too many times with flame on, hits limit, then back on ... board issues 4 blinking red indicating thermal protection device open ... which it is ... too much cool air between cycles.

Submitted: 322 days and 13 hours ago.
Category: HVAC
Value: $9
Status: CLOSED
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Posted by hvacmrfixit 322 days and 9 hours ago.

Answer

Dirty air filter or bad blower

322 days and 9 hours ago.

Reply

Blower working fine ... filters brand new ... cracked heat exchanger ?? temp limit too low?

Posted by hvacmrfixit 322 days and 9 hours ago.

Answer

May be bad limit switch test temperature right above furnace(plenum) and see if its close to 190 degrees

322 days and 9 hours ago.

Reply

I'm not a home but doing office work today ....

 

Final question: If the temp is okay then should I check for a cracked heat exchanger?

Posted by hvacmrfixit 322 days and 9 hours ago.

Answer

It really sounds like a bad high limit switch

322 days and 8 hours ago.

Reply

Okay ... all measured ...

 

Flame on until temp hits 174 F; then back on at 140 F - I used an electronic meat thermometer.

 

However, the diagram sheet attached to the furnace states:

 

Max. Design Air Temp - 165 F

Limit Setting - 155 F

Accepted Answer

I think secondary heat exchanger is dirty and blocking air flow from blower. It looks like a small car radiater above the circulation blower. Slide out blower assemby and stick your head in blower cavity and lool up you should see a dirty heat exchanger ,brush off. While you have blower out clean squirel cage louvers with a old tooth brush(makes a world of difference in air flow) .Disconect power at breaker panel before attenting to pull blower assembly

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Expert: hvacmrfixit
Pos. Feedback: 100.0 %
Accepts: 192
Answered: 12/20/2008

HVAC Technician

30 years of commercial and residential heating and cooling installations and troubleshooting

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