FAN STILL KEEPS RUNNING BUT NO HEAT! - http://www.hvacmechanic.com/ Forums

Original message

sam

24.186.171.49

"FAN STILL KEEPS RUNNING BUT NO HEAT!" , posted Tue 16 Dec 17:12

On the second carrier unit DJA006520(rooftop) I replaced the fan limit switch. Inducer fan blows good. Blower fan works good. AC coil is clean. When thermostat calls for heat, Inducer starts then after 45 seconds or so blower fan starts but furnace doesNOT ignite. Blower does not stop and inducer does not stop. I have worked very hard on this for a few days! I would like to succeed and at the same time acquire precious knowlede! Am I right to say inducer is OK. What is this centrifugal switch/sensor. Where is it? How can I test it? Can it be replaced on its own ? and how? ...... OR what should be my next possibility. What do think the technician did to get it firing the other day?. Can inducer fan really be the culprit even when it seems working perfectly every time! I know I have asked a lot of questions but you see in NY it is COLD/SNOWY and will get worse! and I have a short window and I am a begginer.

Replies:

kdmman

24.64.223.203

"Re(1):FAN STILL KEEPS RUNNING BUT NO HEAT!" , posted Sat 3 Feb 01:14

look for manual reset high limit on fan housing,small disk with red button,push in button

diverdan

68.233.192.171

"Re(1):FAN STILL KEEPS RUNNING BUT NO HEAT!" , posted Sat 12 Feb 20:16

An open upper limit switch will cause those symptoms in some furnaces. Look for a little oblong disk shaped thing with two wires attached to it by the burner assembly. Between the two wires there should be a little button you can push to reset the limit switch. Some limit switches do not have a reset. An OHM meter connected to the terminals on the switch should show a closed circuit if the limit is okay. If the limit switch (flame rollout) is tripping it may be that you have a restricted vent, a restricted secondary heat exhanger, or too much manifold pressure.

xenos
Webmaster

67.71.22.119

"Re(1):FAN STILL KEEPS RUNNING BUT NO HEAT!" , posted Tue 16 Dec 17:29

If could well be the centrifugal switch. It’s actually quite common. This switch is located on the end of the Venter motor. Look for 2 red wires. I think their red. When the motor starts this switch should close bringing on the igniter.

tap on it with a screw driver may help determine if it's it.

Xenos.

The best way to escape a problem is to solve it.

xenos
Webmaster

67.71.22.119

"Re(2):FAN STILL KEEPS RUNNING BUT NO HEAT!" , posted Tue 16 Dec 17:31

What is the model number I will find a manual. You are missing the first 2 numbers Ie. 48DJ...

Xenos.

The best way to escape a problem is to solve it.