I have a Carrier 58SXA that I don't know what to do with next. When the
thermostat calls for heat, most of the time the furnace works. Sometimes
though it just does nothing; no inducer motor, no noise, nothing. It shows
heat on the thermostat but the temperature in the house keeps falling and
the furnace is silent. I replaced the control board. Same thing. I replaced
the inducer board and pressure switch. Same thing. I replaced the ignition
box. Same thing. I replaced the pilot assembly and flame sensor. Same thing.
I replaced the limit switch. Same thing. I replaced the thermostat. Same
thing. I'm stumped. I've checked the wiring down from the thermostat.
Everything is as it should be. Our local Carrier man doesn't know what is
wrong. I haven't replaced the gas valve or wiring assembly. When the furnace
works, it works great.
That furnace was made in about 1986, and according to my local Carrier
wholesaler tech guy, "that furnace had problems". LOL The board was
originally designed to shut the inducer off when the call for heat ended.
Also, the combustion air intake would allow water to drip down onto the
pilot assembly. The replacement board would makes the inducer run for 15
seconds after the call for heat ends. How many terminals does your
replacement board have?
The replacement board has terminals for Y, W, H, R, GH, C, G, EAC-1 and
EAC-2. I've noticed the inducer motor runs for awhile after the call for
heat has ended. I've read some of the problems this furnace has.
Fortunately there is no sign of water dripping on the pilot assembly. I'm
beginning to know this furnace more intimately than I want too..LOL. I
would buy a new furnace but money is the problem.
Bobb, what do you think could be a (the) problem with my wonderful Carrier
I honestly don't know what the problem is, I can't see it from here.
Assuming you have good voltage and gas pressure, if it stops in the same
spot each time it malfunctions, then that's where the problem is. The
thermostat signals the inducer motor relay built into that board you
replaced. You need to put a meter on each terminal, one at a time.
Was "your local Carrier man" a service technician? If so, did he actually
come out and look at the furnace, or did you just phone and ask questions?
If a technician came out, was it malfunctioning when he was there?
A trained tech should have all the right tools and either know or have
available a Carrier "Sequence of Operation". If not, it's available to him
(not you) on the Carrier web site. It tells him what should happen and when.
If it's malfunctioning when he's there, he should have very little trouble.
BTW, unless a heater was damaged by water, lightning, etc., multiple parts
replacements are rare. I understand your need to save money, but if that
furnace misfires, you're in for more excitement than any sane man really
should want. Do yourself a favor and call someone qualified.
If this was already proposed, then disregard.
I didn't read all the responses to your question.
I recall a similar problem back in the late 'eighties when I was doing
residential work. Same deal, intermittent no heat. Turn the power
off to the furnace, back on, normal heat cycle starts and continues to
cycle for undetermined amount of time until next failure. This problem
arose when changing from a mercury switch thermostat like a T87F,
to a solid state control thermostat like a Chronotherm or similar.
The fix: install a 24 volt isolation relay on the W (heat) circuit between
the thermostat (t) and the board (b). When the call for heat satisfies,
the relay makes a clean break between Wt and Wb, same as the old
mercury switch thermostat did, eliminating any feedback or trace
through the solid state thermostat which they were stealing to charge
up a memory chip or battery or whatever they do.
Wt to one side of the relay coil.
Cb (24v common) to the other side of the relay coil
Rb (24v) to relay switch common
Wb to relay switch NO (normally open).
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