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I have a Carrier AC/Heater Unit in my commercial building…

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Hi there, so I have...
Hi there, so I have a Carrier AC/Heater Unit in my commercial building model#: 48SS-036120321AA. The cold has just rolled in and the tenant currently residing in the unit has turned on the heat. The problem that is occurring is that the unit some times works and sometimes doesn't. Its random. Ill set the thermostat to the desired temp and put he fan on auto, you will hear the blower motor start for the fumes running all the time, but its a 50/50 chance of the heater fan actually going on (depending if we get a flame or not). So far I have a cleaned the flame sensor and the other piece of metal next to it. No improvements. There is a led flashing, i get a 1 blink flash (fan on/off delay modified) and a 4 blink flash (5 consecutive limit switch faults). Last night I took the act temperature switch from another unit not being used to see if it would make a difference. The furnace fired up but according to my tenant this morning the heat was not running. I'm left to believe it might be those valve coils just because i had a similar problem like this with a gas dryer I own which it would sometimes fire up. But I thought it would be best to get a professionals input first. Thanks
Submitted: 7 months ago.Category: HVAC
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Answered in 4 minutes by:
11/27/2017
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 23,119
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Hello,

My name is Billy. The unit is firing up...but it is overheating and shutting down....cools...heats ...shuts down...then after 5 times of doing this it locks out into fan only and exhaust motor only and runs that way for 3 hrs...or until power cut and restored.

It could be filters, bad belt (if equipped), motor faulting....pretty much anything that restricts air flow.

And if the limit switch is sticking it will not matter about reset..

Have you checked filters, belts, blower motor? And sometimes the ac coil gets plugged

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Customer reply replied 7 months ago
well i changed the filter in the begining of the summer but ill make sure to give that a look. As for a belt, ill have to check if it has one, is there anything specific im looking for with the belt that might cause this issue? As for motor faulting, are we talking about the motor that blows warm air into the unit or the motor that blows out the exhaust fumes? Because now that you mention it the air that blows into the unit does feel a bit faint. Is there a way of checking if the motor is bad? Thanks
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago

The motor in question would be the circulation blower fan. Let me see if I have a pic for you...just a moment

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HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago

Ok this unit has no belt and is a direct drive.

So I would check the motor in heat mode and make sure it is running.

Check blower wheel for debris

Check ac coil (behind air filters in unit) to make sure not dirty

Check filters

Then note ...was any construction done during the last year?

Excessive drywall or dust?

Were any walls modified/duct?

Your sole point will be to check airflow through the unit from the blower itself running to having fins, coil and filters

Manual HERE

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Customer reply replied 7 months ago
No construction or excessive dust. Nothing modified that i know of. I just alwawys realized there was a lack of air flow, it work and spins, i can see it. What is it exactly that is overheating to cause the shut down though, maybe that is faulty?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago

How about speeding the blower up? According to the diagram in the manual I sent you there is another higher speed available for heating.

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Customer reply replied 7 months ago
oh really, that would help greatly, what page am i looking at and how do i do that? thanks
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago

there are different color wires from the blower motor. Depending how you hook up and the color you use changes the blower speed.

See the red square HERE

If you want to post a pic of the motor and wires I could direct further.

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Customer reply replied 7 months ago
I'm in front of the fan right now and I see the blue black and red wire. I've tried them all but they all sound the same speed. None of them sound noticeably stronger. Would you happen to know which one is the strongest Thanks
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
The high speed is black..med is blue..low is red
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Customer reply replied 7 months ago
Nevermind. Gave it a good listen and realize that black was the strongest. But it was already set on black before I opened it.
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
Then the unit has already been sped up since install as red is shipped heat speed
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Customer reply replied 7 months ago
Coil*
Customer reply replied 7 months ago
Filter isn't too bad either , but I'll replace
Customer reply replied 7 months ago
The Flap is currently open halfway.
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
How are fins in wheel
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Customer reply replied 7 months ago
The outside of the Furnace where the heater metal manifolds are. (I'm not sure what they're called) is extremely hot and unbearable to touch
Customer reply replied 7 months ago
I'll check he fins now
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
The heat exhaust exit will be very hot
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HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
Fins are fine. Does the unit cool ok?
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Customer reply replied 7 months ago
No it does have a refrigerant leak
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
Any smoke dampers?
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Customer reply replied 7 months ago
What are smoke dampers?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago
Commercial units have smoke/fire dampers in the duct. If they close..which many do it decreases air flow
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Customer reply replied 7 months ago
How and where would I check that?
HVAC Technician: BillyHvac, Journeyman HVAC Tech replied 7 months ago

It could be anywhere ...especially where duct passes through walls. There is a damper held open with a link that melts in high temps....however these links can fail under vibration and age and the damper closes.

They can be any size but here is a pic of one click here

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