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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8517
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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58PAV155-15120 carrier keeps blowing the 15 amp type S fuse.

Customer Question

58PAV155-15120 carrier keeps blowing the 15 amp type S fuse. replaced it 6 months ago. Then yesterday. Now again today. Is this the right fuse? Should I try a 20 amp? Should it be a type S and what is the difference?
Hate to get anyone else out to check it out. Also low on available cash if a major expense.
Thanks Tom
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.
Welcome!
You need a T type, *dual element fuse* for anything with a motor in it, however for a furnace that draws less then 5 or 6 amps an S type 15 amp should have lasted.... the fan motor could draw up to 12 or 15 amps for a few seconds when it starts.
http://screencast.com/t/0wZ8ch3Fzvk
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Customer: replied 2 years ago.
The fuse went out again and went to Lowe's to buy several type T fuses as you stated but they are threaded differently when I attempted to install. Obviously the type T do not work.
Expert:  Phil replied 2 years ago.
Hello again,
I cannot see how much electrical current your house fuse panel can handle from here, however most of that that type were 60 amp panels and were fit with the T type fuse, S types were fit into those panels with an adapter.
It will be a good idea to call in a local electrician to look over the total load you have on that panel and on that circuit with the furnace on it by using a clamp around type amp meter.
It is also possible that furnace motor is going bad and drawing more than its rated amps, these older screw in type fuse panels.
Tell me please if you have air conditioning attached to the furnace,
We can go from there without any time limits.
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Customer: replied 2 years ago.
Yes. I have been running my AC the last few days here in Denver having been around 80. The unit is outside. This fuse is just in a small box on the stud wall of the furnace room. My outside panel has a couple dozen + circuit breakers. I have an additional panel in the basement when this area was finished. The main panel is large for a larger house. House was built in 97.
Expert:  Phil replied 2 years ago.
Hello again, your house wiring sounds good, from here at least. It is unusual that an S type fuse box would be installed at the furnace given the upgraded wiring for the rest of the house.
Look on the model/ serial number plate inside the furnace, generally in same compartment as as the gas valve and burners... it will also have the blower amperage on it, listed as FLA, full load amperage, if it says 4 amps, then it will take roughly 12 amps to start the blower motor, called LRA.. locked rotor amps.
If the fan motor is rated at 5 amps, then it will take 15 amps to start the blower. That is close to the fuse limit, (the fuse is built to stand a slight over amperage for a brief time however, but it wears on the fuse)
Look that over let me know what you find,
If you want to go further you can buy a clamp around amp meter for $20 at harbor freight, or a $50 one from a big box home fix up store... and check the current draw on the furnace.
We can go from there, I will pick up your response in the morning if I miss you tonight.
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Customer: replied 2 years ago.
Could not find an FLA in the compartment but the circuit diagram on the cover shows 3 amp fuses. i did also provide the model number as originally specified. Got that from the HVAC guys that came out 6 months ago and replaced a fuse for $140.
Expert:  Phil replied 2 years ago.
Hello again, the 3 amp fuse is in the 24 volt circuit, and is not there to protect the blower motor.
You will need a clamp around amp meter or... locate the model number sticker with the motor amps on it.
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Expert:  Phil replied 2 years ago.
Here is a parts house specification on that motor
http://www.airconditioningheatingsource.com/?ACTION=PartNumber&PN_ID=2519
Motor amp ratng is 11.1 FLA. (we need to verify that however)
That disconnect switch with the 15 amp S fuse needs to be served by size 12 awg wire, and a disconnect switch with dual element 20 amp fuses.
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