[JackOfAllMaster]

Greetings:
I have a Carrier forced hot air furnace and several times a day the furnace won't start when the thermostat calls for heat. Most times turning the stat lower than the room temperature then back higher the furnace will start and run normally for several hours.
I have a Carrier 58SS060CC with a power vent attached. I replaced the powervent in 2000 because the blades had corroded. I also had to replace the fan blade cage for the Induction fan (I think that's what's it's called) a few years ago because of corrosion. I pulled the induction fan out last night to check things and the chamber(?) had a lot of loose sediment in it. I vacuumed that out and cleared the clear rubber tube to the pressure sensor switch(?) The furnace is 27yrs old. I've just replaced the power vent fan relay but that didn't help. I don't have a manual and I'm not sure how to diagnose where the trouble could be. I hate to start replacing parts hoping to get lucky. The stat is a Honeywell RTH6300B installed march 07. We don't run the setback feature anymore because of the furnace problem. Thanks for any advice you could offer.

[hvac1000]

Greetings:
I have a Carrier forced hot air furnace and several times a day the furnace won't start when the thermostat calls for heat. Most times turning the stat lower than the room temperature then back higher the furnace will start and run normally for several hours.
I have a Carrier 58SS060CC with a power vent attached. I replaced the powervent in 2000 because the blades had corroded. I also had to replace the fan blade cage for the Induction fan (I think that's what's it's called) a few years ago because of corrosion. I pulled the induction fan out last night to check things and the chamber(?) had a lot of loose sediment in it. I vacuumed that out and cleared the clear rubber tube to the pressure sensor switch(?) The furnace is 27yrs old. I've just replaced the power vent fan relay but that didn't help. I don't have a manual and I'm not sure how to diagnose where the trouble could be. I hate to start replacing parts hoping to get lucky. The stat is a Honeywell RTH6300B installed march 07. We don't run the setback feature anymore because of the furnace problem. Thanks for any advice you could offer.

The links below are just for your records. They do have a nice wiring diagram and other stuff you might find interesting


http://www.xpedio.carrier.com/idc/gr...it/58ss-1p.pdf


http://www.xpedio.carrier.com/idc/gr.../58ss-6sic.pdf


If your system has a 3 wire pilot it could be causing the problem since they are trouble makers and over the years I have replaced many of them.

Here is a pic of what I am talking about. If you do not have this then it must be a different model than the 58SS.

[wmproop]

At 27 years old,, its time to think about the old girl maybe has seen her last days.
I would be very concerned about carbon monoxide leaking through into your fresh air at that age,, happens to the best of them,, get you a carbonmonoxide tester/warning device and install. I try to recommend these after a gas furnace reaches 18 years old

[JackOfAllMaster]

The links below are just for your records. They do have a nice wiring diagram and other stuff you might find interesting


http://www.xpedio.carrier.com/idc/gr...it/58ss-1p.pdf


http://www.xpedio.carrier.com/idc/gr.../58ss-6sic.pdf


If your system has a 3 wire pilot it could be causing the problem since they are trouble makers and over the years I have replaced many of them.

Here is a pic of what I am talking about. If you do not have this then it must be a different model than the 58SS.

Thanks hvac1000. I do have that 3 wire pilot assembly you mention. Is is something that needs to be cleaned or should I just replace it?

[JackOfAllMaster]

at 27 years old,,,its time to think about the old girl maybe has seen her last days.
I would be very concerned about carbon monoxide leaking thru into your fresh air at that age,,,happens to the best of them,,,get you a carbonmonoxide tester/warning device and install. I try to recommend these after a gas furnace reaches 18 years old

Thanks wmproop. I agree. I started getting prices for a new furnace just before the holidays.. then the ice storm hit (great northeast). Next thing I knew... 10 below. I probably will have a new unit installed in the spring... when it's warmer.. =).

[hvac1000]

Thanks hvac1000. I do have that 3 wire pilot assembly you mention. Is is something that needs to be cleaned or should I just go ahead and replace it?

Replace but in the mean time you might tap on it to see if it will work.

[JackOfAllMaster]

Well I finally figured out what the problem was. My furnace installation uses a power venter unit where the flue pipe exits the basement side wall. The power venter is a PVG series by Field Controls and has an internal relay (in addition to another relay which feeds the 120 line voltage - more on that later). After checking 120v line voltages and the 24v thermostat voltages at the power venter during the time the furnace worked and the times it didn't (and realizing the problem occurred more frequently when the outside temp was coldest) I came to the conclusion the power venter internal relay was bad. To test my theory.. I removed the 120v line L1 from the L terminal (at the power venter) and placed it on the M terminal (basically bypassing the power venter internal relay) and sure enough every time the TStat calls for heat now the furnace works. TStat calls for heat.. the power venter starts right up... after a few seconds the furnace ignites then the blower starts... all is well. I did however discover that whoever installed the power venter unit originally, incorrectly installed a second 120v relay switch to feed the power venter. What's happening is as soon as the Tstat shuts the furnace down the power venter shuts right down as well without continuing to run a few extra seconds in order to purge the flue pipe. It looks like the line voltage to the power venter should be an unswitched supply. Thanks to all those who gave assistance...

[hvac1000]

Glad you got it going.