Furnace won't come on after being off several hours, new relay
Have an old Carrier made BDP hvac. When it has been off several hours, it will not come on again until I switch the breakers off, then on. Then it runs fine while cold out, but if we have a warm day and it's off for many hours, it does the same thing. I had the problem years ago and replaced the relay (common 90340 24volt) and that fixed it. So, I replaced the relay, seemed to come on immediately, but when it was off yesterday during a warm day, had to cycle the breakers. Then it comes on and off fine during the cold night until stopped for a while. This is ancient, 1985 model, would like to nurse it along for a while longer, it heats well. Anyone know what to try? I don't think it's the thermostat, but it could be. Its the old mercury type, pretty simple, and it does work after starting up for the first time. But, when I leave town for a couple days, with it turned way down, I find it cold in the house and it did not come on at the low setting during the colder nights after being off in the warm days we often have in north Texas. Help!
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Re: Furnace won't come on after being off several hours,...
Lets test the t-stat. Take the cover off the stat locate the terminals R & W take a small piece of wire and holding the wire jump across the two R & W terminals. Does the furnace start up immediately? or does the same problem exist? Sometimes in diagnostics you have to start to eliminate the problems one by one. ken
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Could be several causes.
1. Blockage on piping
2. Water in inducer housing slowing down inducer impeller
3. Condensate trap for furnace clogged up.
4. Inducer motor going bad.
5. Leak in vacuum hoses or not connected. Welcome To the Best HVAC
If I am correct, that is a gas furnace, right? I believe it may be between 15 and 20 years. Pro-active with and older gas furnace is never a bad thing. First of all it can become a safety issue, as concerns of heat exchangers cracking and leaking carbon monoxide into the home become increasing. Second, it sure only be 80% efficient, whereas a new condensing furnace today can be up to 95% efficient. That means that you currently only use 80% of the gas you are burning as actual heat transferred into the house via airflow, and the other 20% is literally leaving the house through the flue. So you can increase efficiency dramatically and be safe at the same time by replacing pro-actively
you have a flame rollout switch tripped or a limit switch open. in either case you should call a hvac service company. how old is your unit? the carrier unit is designed to run the fan contin. in the event of either of these failures.
Double check that the new contactor has the same electrical ratings on it. My guess is that the coil should be 24v while the relay should be able to carry the same amperage at 220v.
First shut off the breaker and disconnect switch for the furnace and outdoor condenser and call a licensed HVAC contractor:)
If you are determined to do it yourself, Then read the schematics first. Be aware, if you mis wire the system you may cause more damage than you have now. Not to mention your personal safety is at risk.
I am basing this on the most common style contactor found in my area.
The main relay side should be labeled. (eg. L1,L2-T1, T2). These should match exactly like the old one. L1 and L2 are the incoming power. T1 and T2 are the power leaving the contactor. All the 220v wires should correspond to one of these four terminals either by screwing them down or fitting the spade connectors together.
Usually the 24v wires will plug onto the coil (near the bottom, left and/or right sides of the contactor) silver spade connectors.
(STEP 1.) Leave all Wires Connected to your Old Contactor.
(STEP 2.) Remove the two mounting screws that hold the Old Contactor to the Air Conditioners casing.
(STEP 3.) Now Install the New Contactor to the old contactors existing location using the Same two Screws.
(STEP 4.) Now take Off one wire at a time from your old Contactor and
Install each wire one at a time to the proper location on the new