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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: 337 days and 14 hours ago.

Category: HVAC

Value: $9

Status: CLOSED

Posted by hvacmrfixit 337 days and 11 hours ago.

Answer

Dirty air filter or bad blower

337 days and 11 hours ago.

Reply

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

Posted by hvacmrfixit 337 days and 11 hours ago.

Answer

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

337 days and 11 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 337 days and 11 hours ago.

Answer

It really sounds like a bad high limit switch

337 days and 10 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

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

HVAC Technician

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

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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.

Answer

Dirty air filter or bad blower

Reply

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

Answer

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

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?

Answer

It really sounds like a bad high limit switch

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 FLimit Setting - 155 F

Accepted Answer

Related HVAC Questions

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?

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