Heating, Air Conditioning, Fridge, HVAC/AC fan blower does not shut off


I have a Rheem Criterion furnace/ac unit built in 1992.
When the AC gets to my set temperature the cooling turns off but, the blower keeps on running.
I replaced the thermostat with no change to the problem. I called in a AC company here to check it out. The tech told me that the problem is in the Circuit Board and would be $750.00 to replace.
Question, is the tech on the right track? Is there another cause for the blower to not shut off?


 The Blower on that and most all modern gas furnace or air handlers is controlled by the circuit board.  In the heating mode, the board will use an internal timer to energize the Blower, that starts as soon as the "lighting" sequence gets to the point where the burner with the Flame Sensor has received the necessary heat and the board reads the millivolts from that sensor.  It then starts another timer, when the "W" wire from the thermostat stops "calling" or stops sending the low voltage to the W connection on the board, and that timer is to allow the Blower to send the last little bit of heat from the heat exchanger into your home.
 The other way the Blower is energized is from a "call" for it through the green wire to the G terminal on the board.  That green wire comes from the thermostat "G" connection, which is a connection to the Fan switch , either manually when you move the indicator to the "ON" position or when the thermostat sends a signal ( low voltage ) on a "call" for cooling to come on.
 The other way it can stay on all the time is if there is a limit switch of a safety switch to be "tripped"  That will happen because the board is protecting the furnace from over heating, by locking the Blower ON and preventing the Gas part of the furnace from working.  
 There are LED lights on the Board that will flash a signal of a repeating number of flashes that you count and then look on the inside of the door to your furnace and you will find a ledger that tells you how many blinks or flashes are what.   Example......4 flashes is a limit switch, 5 might be the flame sensor and so on.
 Depending on what Criterion you have, the color of led's used and number of flashes will tell you a different thing.  So you need to look on the inside of the door that covers the blower section.  ( If it is not there, look on the inside of the other door.)
 I would ask the tech to show you the flat rate book he is getting the price out of just to make sure.  And make sure he is using the correct part number and the correct column, not that I think he is pulling a fast one, but that there are a lot of boards and some are way more than others and it is possible to not use all the right info retrieving the costs from the flat rate book.  

---------- FOLLOW-UP ----------

QUESTION: On my board are two LED lights. One is for power and one for system ok. Both lights are a solid green.
I noticed also that the green wire from the thermostat is not connected on the circuit board. I do not remember if it was that way or not before the tech came.
My Criterion is probably a first as there is not letters after the name. As I mentioned it was made in 1992 as home was built in 1995.
I am not trying anything with the heat right now only the AC.
House gets to set temp and the condenser fan shuts off but, the blower keeps on going until I unplug the furnace.

 If there is a green wire that is not attached, the tech took it off to trouble shoot and didn't put it back.  I know you are not in the heat mode, I just told you all the ways you could have those symptoms.  
 Because of the cost of that repair, I would be over the tech's shoulder if I were you, armed with the knowledge I have given you and make sure it is not a safety instead of the board and that he is using the correct price in the flat rate book.  I cannot do any more than that over the internet, I am sorry.

Heating, Air Conditioning, Fridge, HVAC

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john t. borgman


I am in Portland Oregon at Ben's heating 503-233-1779. I work days, so I can only answer early in the day or later in the evening. I only answer public questions for residential equipment. I am very well versed in gas, electric and heat pumps and will only answer residential applications. I have been known the past decade or so, by my employers as the guy you send when no one can figure it out. Trouble shooting is my special. I understand the physics behind air flow, refrigerants and electricity. I understand programmable t-stats, zone controls, economizers, fossil fuel kits and the engineering thought process in the wiring and construction of residential equipment


I was lucky enough to start in this field almost 30 years ago as an installer, for a company that installed the best duct systems I have ever seen, even to this day. The best ,as far as understanding the way air really flows through a duct system, from the return air to the very last supply register . They also had great pride and the duct work was put in, not only to last 50 years, but to look exceptional. Then as I started doing service work, I was again fortunate that I found a 3 year engineering class being put on be a man that was the educational director for the Entire united states for a society called " the Refrigeration Service Engineering Society " And for the next 3 years I schooled at night and practiced what I learned during the day, a great advantage over schooling and then trying to remember it years later.. Versed in duct design manual J heat gain/loss calculations.

Refrigeration Service Engineer's Society

I have 2 inventions that have gone through the process and been recorded at the National Institute of Standards and Technology from start to finish and thus been invited to national innovation workshops by the dept. of Commerce and the dept. of Energy. They are waste heat recovery devices that N.I.S.T approved as valid and am currently looking for marketing partners to get this product into the hands of consumers and make a BIG difference in Energy savings for every Household and Eatery and take a big bite in the the peak hours power consumption that face our Utilities companies.

factory training in Lennox ,Rheem, Ruud ,Trane, Tempstar ,Carrier, Day&Night, Payne, Bryant, Coleman, Intertherm, York, Goodman, Ultra boilers, Unico, Mitsubishi,Sanyo, Taylor, Nicewonger, Navien. Associates degree in Refrigeration Engineering. Certified with Energy Department, Check-me Program, P.T.C.S (performance tested comfort systems ), have N.A.T.E. certifications in gas, a/c & heat pump.

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