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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8316
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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The AC fan will not turn on. I can get the fan and furnace

Customer Question

hi the AC fan will not turn on. I can get the fan and furnace to operate but when I go to Fan and AC or Auto and AC the outside compressor is running but no fan in attic is running as it sould. Since fan works for heat and not on AC I assume the thermostat is bad It is very old Honeywell Cronotherm 3 maybe over 20 years old Am I correct?
JA: Sometimes HVAC issues that that you think will be really complicated end up being easy to fix. The HVAC Technician I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the HVAC Technician should know?
Customer: NO i think my summary is good to go
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Are you saying the INDOOR fan does not run in AC mode?

Customer: replied 1 year ago.
the indoor fan in the attic mounted unit works fine if in heat mode and thermo position
BUT when I go to try to run AC the outside compressor unit with fan included in it runs slowly but the attic fan does not come on so no air is distributed thru the vent forced air system inside the house.
I switched back to heat and fan and furnace fired right up but no joy on AC air fan distribution
Expert:  airheatman replied 1 year ago.

OK since fan runs in heat mode, we know motor is probably ok. Issue is most likely going to be a bad relay (often built into the control board).In heat mode and fan mode different relays activate the fan than in cool mode. Do you have a volt meter so we can verify and do some troubleshooting?

Customer: replied 1 year ago.
I do have a voltmeter.....attic is not easily accessible for me.....old and fat issue.
Anyway to eliminate the thermo first??
Expert:  airheatman replied 1 year ago.

Issue is not with thermostat if fan comes on in FAN On position and outdoor comes on in COOL position.

On call for cool the thermostat signals the indoor fan to come on and outdoor unit .If outdoor is coming on, the thermostat is sending the signal.

Expert:  airheatman replied 1 year ago.

Lets just verify though. We can go to thermostat and touch the G and R teminals together with a wire or pair of needle nose pliers and see if blower will come on.

Customer: replied 1 year ago.
ahhhhh understand.........I am not feeling comfortable to work in attic. Very hot up there right now.
When it cools down what am i looking for?
I am good tech guy Ran Suzuki service op for 40 years so comfortable with meters and tools etc
When is the relay located? Furnace is original 1982 model so parts may be an issue too
Expert:  airheatman replied 1 year ago.

First step is to determine if we have a control board in the furnace or just fan relays.(I can tell that by model number).

2. If we have a board fan wires will be connected to terminals on the board marked HEAT COOL FAN and NEUTRAL.

3.On call for COOL we want to check between the NEUTRAL where fan wire connects and COOL terminal where fan connects. If we are not getting power out of board the relay for high speed is stuck open and board will have to be replaced.

4. If we do not have a board, basically same thing but instead of a board we will be checking power through the relay.

Customer: replied 1 year ago.
OK getting somewhat complex Let me see if I can get in attic when it cools off and get furnace info from model and brand plate then tomorrow I will email you back with needed information Work for you
Expert:  airheatman replied 1 year ago.

I am actually leaving in the morning to go camping but I can open this to other experts who will be able to pick up and work with you from here

Customer: replied 1 year ago.
OK Have a great time. I am avid camper too.....Enjoy and thanks for your help today!bestJim
Expert:  airheatman replied 1 year ago.

Thanks Jim .I am going to opt now so another expert can help if I am gone wen you return.

Expert:  Phil replied 1 year ago.

Hello, I am picking this up from Airheatman. If you can take a photo of the fan motor wiring where it plugs into the printed circuit card, so that I can see the entire rest of the card, and where the thermostat wires connect....I can coach you as needed.

Use the paper clip icon at the right end of the tool bar for that, or the 'attach files' link to the left of your send button.

We can go from there.

Customer: replied 1 year ago.
Hi Phil. Been gone all evening. Will tackle your request and guidance in AM.
Expert:  Phil replied 1 year ago.

Thats a good plan, see you later this morning.

Customer: replied 1 year ago.
OK Tired to get up in attic this AM NO go! So I called a repair guy in...hated to give up............
He found one weak capaciter not quite up to spec and a bad Relay. Funny weird deal is he had a spare on the truck as they work this area a lot. He installed that and it was BAD Had to go get another off the truck and that fixed it. Been running smooth all day...Was 104F today so being fixed was so welcome Thanks for all the help!
Expert:  Phil replied 1 year ago.

Good work, glad you got it fixed.

If you care to rate my assistance by clicking on the 'rate your expert' link I will appreciate it, its how I earn a living and will not increase your charges.

Expert:  Phil replied 1 year ago.

Rating my work also allows you unlimited follow up on the same dime should you need it later. I hold the question open to your in those cases

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