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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8530
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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i live in new port richey florida in an older concrete block

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i live in new port richey florida in an older concrete block home, i have an older gibson (about 7 - 10 years old) a/c unit and air handler with a honeywell programable thermostat. The unit cools the house fairly well, i have cleaned the condenser coils outside and the evaporator coil inside and made sure the drain is clear the filter get changed once a month. I try to keep the thermostat set between 78 - 80 during the day until the wife gets home and then she drops it to 74 thinking it will work harder to reach the temperature quicker(dont tell me i already know ! if you are married you will understand this). here are my questions the house has new windows it could use more insulation in the attic and the kitcehn to garage door could seal better but it has a very hard time trying to get to 76 it will get there but i think it takes a long time. also how long after the compressor shuts off should the fan in the air handler run
Welcome back to Just Answer !.

There are several issues here.

In Florida, with the fan and air handler running, and leaky duct work (no duct work is 100% leak free), you end up drawing hot humid air into the house....that can run your cooling bill way up, and warm the house up faster than if you set the system so that the fan goes off when the condensing unit outside goes off.

Without the fan running, the cooler air stratifies near the lower part of the rooms, so that in the summer that is an advantage for seated people.

In the winter however the warm air stratifies at the top of the rooms, and by running the blower all of the time you get the warm air mixed into the lower part of the room keeping the entire house warm.


Summary: I would set the fan switch on the thermostat to 'auto' so that the blower only runs when the system is actually cooling.

Exceptions: IF someone were to set the thermostat down to 70F at night, on a cool night, but with the house still above 70F inside... the cooling coil will run below freezing , and develop a big ice ball around it. That is not good.

If you have the fan set to the 'fan ON' position, the fan will run all the time and will melt the ice ball once you turn the outside unit off... that of course is not normal operating conditions.


There are thousands of controls variations on the market relative to how long the fan runs after the cooling unit shuts down... 99% of them turn the blower off when ever the outside unit shuts down.

There were some systems built that ran the inside fan for a few minutes after the cooling unit shuts down however..

and of course... the fan relay could fail and stick closed and run the fan all the time even with the fan switch set to 'auto'... that would be a defective fan relay.

Let me know if this makes any sense on your end or not, we keep going until you have all of your questions on this answered.


Phil and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

the fan is set to auto, the inside fans usually runs for awhile and then shuts off, is there an easy way to identify the fan relay there are several in the air handler Im assuming the one with the wires that go directly to the blower, thses is no relay circuit board in this unit it is an older air handler

Hello again, your assumption is correct... one of the wires from the fan goes directly to the fan relay.

You can find the fan relay on the wiring diagram glued to the inside of the furnace service panel.

The fan controls are a bit more complex than it appears however... these fans are wired for two speeds... low speed comes on when the fan relay is de-energized ... and the furnace fan and limit switch warms up and closes contacts and runs the fan in low speed mode.

When the fan relay is energized (in cooling mode) the relay opens the circuit to the low speed windings and furnace fan control .....and closes a set of contacts that put power to the high speed windings.

That is how 99% or more of these systems are wired... there should be no time delay involved... if there is it will be shown on the unit wiring diagram as time delay relay... that is very unlikely.

If the fan stays running after the cooling unit goes off, then it i is most likely the contacts on the fan relay sticking, or the contacts in the thermostat sticking, or the fan is running on low speed due to a defect in the furnace fan controls for low speed.

Tell me please how long the blower runs after the cooling unit outside goes off..and if the delay is the same each time or not.

Let me know which seems to be the case on your end. we can go from there.


Phil and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

the fan only has one speed, it usually runs for a few minutes afler the compressor shuts off. this morning i noticed it was running longer than usual, so i changed the filter and reset the program on the thermostat, i noticed the batteries were low. so i changed the batteries and reset it it now seems fine. thats why the question, the last time i was in there i changed the fan motor capacitor, i noticed there were 3 relays they all appeared the same and i did notice the diagram for the wiring. the compressor though i cant read the model number it is faded badly i think it is a 2.5 ton though

Customer: replied 4 years ago.

well i am thinking it is a sticking really i just rapped on the air handler and the fan stopped it was running for more than 5 minutes after the compressor stopped so i rapped on the top or the air handler where the relays are and the fan stopped running

Hello again,

It is most likely a sticking relay...those have 5 wires attached. 2 small ones to operate its 24 volt coil.. and three wires that go to the swtiching contacts.. its called a fan relay. those are available at Grainger Industrial Supply for 11 dollars.

It is important that you understand the wiring when replacing it though.. the contact arrangement is generally printed on the side of the relay, or is embossed on the top between the actual wire connections.

Or... you can remove the relay mounting screw, and remove the single screw in the back of it, and take the guts out.. (leave all the wires connected)... and use a nail file to clean up the burnt contacts.

do all that with the power off of course. Stay in touch as necessary.


Customer: replied 4 years ago.

thts exactly what i did i made a schematic before i took it out and used sand paper and contact cleaner it was 5 terminals this is what it looks like


---- 10ga blue terminal # XXXXX


10ga orange terminal #2 I I brown 14ga. terminal # XXXXX


dble blue18 ga terminal #1---- ----- 18ga green/white terminal # XXXXX

feeds additional relay


the only part # XXXXX have on the relay is W-R/RBM


3/4 HP 125 vac

1 hp 250v

25a res 277v ----- 4

I 2 I 5


----- 1 ----- 3

will the numbers be the same that correspond to the wires if it is a different brand relay

Hello again,

Its complex doing this by these obsolete relay part numbers... it is safer and easier doing it by taking the old relay apart and noticing the following things.

- which two wire terminals attach to the coil. 1 and 3 in this case (the 18 gage thermostat wires in this case). 1 and 3 in this case should be wire terminals on the same device that has terminals 2,4 and 5 on it... 1 and 3 would be the coil wires..not an 'additional relay'. please confirm.

- and which of the heavier wires goes to the common terminal on the double pole switch. (that is the terminal that is attached to each of the contacts.

- and which wire is attached to the contact that is closed to the common terminal when the relay is just sitting there with no power

- and which wire is attached to the remaining terminal... that only closes to the common terminal when the relay is energized..


The numbering 1-5 is generally standard in the industry for fan relays of this type... so you can generally go by those numbers alone...but do confirm them by examining the relay itself as i have mentioned above.

You can buy a new one at Grainger industrial supply or Johnstone supply... it will work as long as it is called a 'fan relay, STDP, (single throw, double pole) with a 24 volt coil) and has the same terminal numbers and is rated for 250 volts and at least 3/4 HP (most are).

You can also take your existing relay in and ask for a match up... they may or may not have an exact replacement according to shape, but they will have one with the same terminals and a 24 volt coil, and in most cases using the same numbers 1-5... confirm it by noticing how the relay is wired internally however..

There is no substitute for your own observation however, just examine the relay to see how its contacts work..

Since however the relay was merely sticking, cleaning up the contacts should get it working well again for another few years, that is unless the contacts were burnt too badly to clean up with a file.

Let me know what you think, we can go from there.


Customer: replied 4 years ago.

i and 3 are the wires that go to the coil for sure

Hello again, just follow my directions to confirm which terminal is common between the 2, 4 and 5 ..go buy a new relay as detailed earlier and replace it.

Have you removed the back cover on the relay and taken it apart and found the contacts and cleaned them? Give me the details on what you found .

Any of the vendors mentioned earlier can fix you up with a replacement... print my previous post out with the specification and they will have the relay.

Customer: replied 4 years ago.

thanks for your help it is working now but i will replace it in the morning

Customer: replied 4 years ago.

i just googled the part# 134-10103-333a and it is still valid white rodgers $39.99 retail

Good work! They are getting quite a premium for it though.

Stay in touch.