A/C Fan Runs Permanently - HVAC - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 08-13-2011, 08:32 PM   #1
Newbie
 
Join Date: Aug 2011
Posts: 8
Rewards Points: 10
Question

A/C fan runs permanently


I have an outside Carrier A/C compressor. Inside I have a RUUD heater that has the blower for both the AC and heater.
All is controlled by a RiteTemp programmable thermostat. The thermostat has a fan switch for On and Auto. I have it in auto all the time.
Recently (in Aug 2011) the fan simply did not turn off when the AC stopped. It runs all the time. The AC turns on and off as temperature goes up or down and the air is col as it should be, but the fan is on all the time. I was told two things could be wrong: the thermostat itself or the Relay for the blower motor.
The relay is part of a Honeywell control unit with a transformer and the relay, al connected to a switch like the normal room switches. I can turn off the fan with that switch.
While the fan is running, if I remove the thermostat unit from its mounting on the wall, the fan continues to run, so it seems the thermostat is not the problem, because that unit is not sending the signals to the relay.
The relay is an ESSEX RBM 184-20103-301L, 24 V.(obsolete). It looks like the replacement is a Steveco 90-370 (with 5 contacts). I removed the relay and tested the contacts with an OHMeter. 1 and 3 conduct, 5 and 6 conduct, 2 and 4 do not conduct, and 4 and 6 conduct as well as 4 and 5. So it seems the relay is not sticking when it is disconnected.
Is it possible that the relay sticks only when it is connected?
Is there any other component that could be the problem? and How to I confirm what it is?
Thanks in advance for the help
C.A.

Advertisement


Last edited by cparias; 08-13-2011 at 08:37 PM.
cparias is offline   Reply With Quote
Old 08-13-2011, 08:38 PM   #2
Member
 
JJboy's Avatar
 
Join Date: Oct 2010
Location: Austin - Texas
Posts: 1,402
Rewards Points: 500
Default

A/C fan runs permanently


on the relay body you can see what pins should be on and close.....
make sure your test follow the drawing on the relay body

Advertisement

__________________

**Always kill the power ** Hot air rises, but heat will always move from higher to lower temperatures. ** Real man shoot in manual. ** If it ain't grounded, it ain't dead.
JJboy is offline   Reply With Quote
Old 08-13-2011, 10:01 PM   #3
Newbie
 
Join Date: Aug 2011
Location: Jersey Shore
Posts: 12
Rewards Points: 10
Default

A/C fan runs permanently


the furnace must be older as it is not using a printed circuit board to control the fan,never the less....
- remove the green wire to the low voltage terminal strip...does the fan continue to run?
....if so the t-stat is not the problem.

-check the fan/limit control(rectangular metallic box on the fire wall) if, there is a white button...I think it is in for auto and out for fan. Make sure it is in the auto position.

-if it is still running...check for 24v at the coil of the relay..if not...then the normally open relay contacts for the high speed blower is stuck closed and must be replaced.....sometimes you can hit it w/ the but end of your screwdriver to unstuck it but I would replace it,as it will probably stick again.
SAMCRO is offline   Reply With Quote
Old 08-13-2011, 10:06 PM   #4
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000
Default

A/C fan runs permanently


1 and 3 are the control coil with the stat still off the subbase slowly plug the relay in see if it powers up CLICKS and the fan runs..then its a control wire calling not the relay being welded shut some place R is hitting G from the furnace up to the stat.disconnet the 24V wire run out of the furnace coming from the stat and do the relay plug in test again..if the fan runs its something in the board if not the run is touching R/G calling fan in
biggles is offline   Reply With Quote
Old 08-13-2011, 10:18 PM   #5
Member
 
Join Date: Aug 2011
Posts: 729
Rewards Points: 500
Default

A/C fan runs permanently


Is this a gas furnace? If not then there is another component in the fan circuitry.
If its a gas furnace, power down the unit, remove thr green wire at the wire nut, or terminal strip. Tape it off to keep from shorting out. Take the thermostat off, and turn the breaker on. If the fan runs then the relay is stuck. If the fan doesn't run then hook the green wire up. If it runs after that, then the green wire is shorted to the red. You will have to try another wire in the tstat harness if one is available.
Master of Cold is offline   Reply With Quote
Old 08-16-2011, 10:29 PM   #6
Newbie
 
Join Date: Aug 2011
Posts: 8
Rewards Points: 10
Default

A/C fan runs permanently


Thanks all for the replies.
Master of Cold: Yes, it is gas. I took off the cable connected to the G terminal (it is not green, but blue and it goesto the G terminal in the Thermostat) in a small board on the transformer' secondary side. Thermosstat is off the base too. Braker on... fan runs... so it seems the relay is stuck.
Biggles: Thermostat off, removed the relay and slowly plugged the terminals 2 and 4.. and the fan runs. It seems that these terminals are shorted becuase terminals 1 and 3 are not even receiving voltage form the transformer secondary.
Samcro.. I tried hitting the relay while the fan was running, but it would not open the circuit..
So I am replacing the relay.. I will update when I receive it.
cparias is offline   Reply With Quote
Old 08-18-2011, 10:55 PM   #7
Newbie
 
Join Date: Aug 2011
Posts: 8
Rewards Points: 10
Default

A/C fan runs permanently


I got the RBM Steveco 90-370. Replaced it and the fan continues to run permanently.

I tried to re-construct the wiring and I came up with the attached picture.

There is s mall board on the secondary side of the transformer in the center of the picture. The primary receives 120 V and the sec produces 24 VAC between terminals C and R. This transf and the Relay are both part of a unit. G W and R seems to be just stand alone contacts to be able to hook various cables in them.

If I remove the Relay and turn on the switch (with Thermostat off the wall) I measure 24 volts AC between C and R, No voltage between C and G or R and G.

I removed the G and R wires that go to the Thermostat. The fan still runs, when I turn the switch on.

According to this diagram (i hope i did not miss anything) the blower should work only if contacts 2 and 4 in the relay are shorted by 1 and 3 receiving voltage, but that would only happen if R and G touch thru the thermostat. But since I disconnected G and R form the small board, I do not see how 1 and 3 would receive voltage to actuate the contacts 2 and 4.

Can any one please interpret this for me.?

Thanks

Last edited by cparias; 08-21-2011 at 04:55 PM.
cparias is offline   Reply With Quote
Old 08-19-2011, 05:58 AM   #8
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,467
Rewards Points: 4,580
Default

A/C fan runs permanently


Your drawing shows a circuit that can't work.
beenthere is online now   Reply With Quote
Old 08-19-2011, 09:16 AM   #9
Member
 
biggles's Avatar
 
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000
Default

A/C fan runs permanently


if the toggle switch for the furnace is on there always will be 24Vs on R to C thats a constant supply the other readings with no voltage 24v is the result of the stat off the wall and wires disconnected within the furnace...all 24V..... he furnace is basically stand alone with everything disconnected coming into it... QUESTION do you have 24Vs on 1-3 disconnected off that relay..do you have 115Vs to ground on either 2-4 contact wire...how many terminals are on tht new relay i goggled it it showed 1-3 coil.... 2-4-...5 as common your diagram show you hooked uo to 2-5 N.C.and missing the 115V black into the motor

Last edited by biggles; 08-19-2011 at 09:18 AM.
biggles is offline   Reply With Quote
Old 08-21-2011, 01:36 AM   #10
Newbie
 
Join Date: Aug 2011
Posts: 8
Rewards Points: 10
Default

A/C fan runs permanently


Biggles.. Thanks for the feedback.. I made a couple of mistakes in the previous attempt to reconstruct the wiring diagram.
I have not changed anything in the original wiring.. I missed the yellow wire that comes out of terminal 4 of the Relay, and the white wire coming from the blower at the bottom is actually connected to the live white wire (120V) in the switch box. Most of the connections are inside the Switch box.
Also what I drew as the Honeywell Transformer is an approximately 4" by 3" by 1" aluminum box with two sets of cables coming out of it. I am not able to see the specs.
The GAS 24 V is what I see next to the Gas pilot switch.

To answer your question if there is voltage between 1 and 3. I removed the relay (the new one now) from its socket, removed the thermostat form the wall mount and turned the switch ON. There is no voltage between 1 and 3 on the socket. This is because there is no voltage between C and G. But there is 24 V AC between C and R, which makes sense. There is not voltage between C and G or R and G.
What I can't see clearly is why, if I have the G wire (Blue) out and the R wire (Red to Heat Power) out, with the Switch ON, and I plug the Relay into its socket, the blower starts to work. I have not changed the original wiring that came with the house more than 15 years ago.

I am not sure what the 3 wires coming out of the blower are. The white wire goes to the live 120 V, the black goes to port 2 of the Relay, which is open with respect to 4, so there is no continuity there; and the Red wire from the blower goes to the Honeywell transf (primary) and back to port 5 of the Relay, which is shorted with 6 and then 4 to the yellow wire which connects to the black from the switch, so it seems like the blower White and Red are receiving 120V, but the blower black only receives any voltage if the relay's 1 and 3 get 24 V AC (?)

What am I missing? If you want me to get some measurements, please tell me which wires or terminals you would like to check and whether I should remove or replace either the relay or the thermostat ro have the switch on or off. or if you would suggest to change something

Thanks again for the help.
Attached Thumbnails
A/C fan runs permanently-fan-control_0820a.jpg  
cparias is offline   Reply With Quote
Old 08-21-2011, 08:46 AM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,467
Rewards Points: 4,580
Default

A/C fan runs permanently


What you have drawn as a transformer with a question m ark, could it be a sequencer, time delay relay, or other thermal disc switch to run the fan in heat mode? If so, it may be stuck shut.

Ohm the 2 wires to it, it they read no resistance, its probably a time delay relay for the fan in heat mode.
beenthere is online now   Reply With Quote
Old 08-21-2011, 09:32 AM   #12
Member
 
Join Date: Oct 2009
Location: Nebraska
Posts: 2,362
Rewards Points: 1,000
Default

A/C fan runs permanently


Guessing that top "transformer?" is the limit and it's faulty.
Marty S. is offline   Reply With Quote
Old 08-21-2011, 10:01 AM   #13
Newbie
 
Join Date: Aug 2011
Posts: 8
Rewards Points: 10
Default

A/C fan runs permanently


Ok. Now I understand what SAMCRO said about a metalic rectangular box in the fire wall.. I do not see any white button on the box itself.
This box has two sets of wires, on the one had they go to the 24 V AC terminals in the Gas pilot switch area (right side) and the small board on the secondary of the center transformer; the other two go to the blower and relay.
Beenthere: which cables do I test with the Ohmeter?..
Does anyone know how to remove this box? it seems to be glued to the furnace wall. Is there a way to remove just the cover to see the inside?
How do I test that it is faulty and what would be the name of this device to look it up for purchase.. I already replaced the Relay assuming it was stuck. Although the measurements I took earlier with it unplugged did not indicate it was shorted between terminals 2 and 4.

Thanks.
cparias is offline   Reply With Quote
Old 08-21-2011, 10:16 AM   #14
Member
 
Join Date: Jun 2010
Posts: 141
Rewards Points: 75
Default

A/C fan runs permanently


just wondering?do you see a limit switch anywhere?this is a feature that runs the fan until the last of the heat is used up,before the fan turns off.
Marbledust is offline   Reply With Quote
Old 08-21-2011, 10:19 AM   #15
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 26,467
Rewards Points: 4,580
Default

A/C fan runs permanently


The wires on the left, if its a L4064B fan limit.

Is it about 3" wide and 5" tall?

Advertisement

beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
Marbledust (08-21-2011)
Reply

Tags
ac blower always on , blower fan , blower motor on


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
a/c runs for many hours maybe return vent issues ddeennis HVAC 24 08-02-2011 05:54 PM
Securing Cable Runs Over Block jkoll42 Electrical 2 03-15-2011 06:59 PM
runs and sanding oscarMadison Painting 1 02-24-2009 06:46 AM
PEX Manifolds: home-run to each fixture vs grouping runs? drh Plumbing 3 04-02-2008 04:44 PM
Remodeling upper...existing runs to the basement? wease Electrical 3 02-11-2007 11:49 AM




Top of Page | View New Posts