reluctant inside blower - AC mode

Reply

  #1  
Old 06-14-19, 01:27 PM
Member
Thread Starter
Join Date: Jun 2019
Location: USA Los Angeles
Posts: 5
reluctant inside blower - AC mode

Hi, new here, and I will try to give as much info as I can about my central AC problem. The outdoor unit seems fine. The indoor part is a furnace/AC combo, and the inside blower refuses to work, but only in the AC mode. Heat works great. In all cases, whether it's jumping "R" to "G", manual fan mode etc., the moment the thermostat clicks in cool mode, the blower shuts off. I already tried switching thermostats with the same result. I replaced the White-Roberts control board last winter, and never tested the AC until recently. I suppose it's possible that I accidentally switched or moved a board connector, but I really made an effort to NOT do that. I did notice that there is no connector on the "cool" pin, but I am pretty sure it was like that back then. I've supplied what I believe are appropriate pics, if this helps. Thanks in advance!

Name:  f2.jpg
Views: 38
Size:  75.1 KB
 

Last edited by PJmax; 06-15-19 at 08:42 AM. Reason: removed un-needed pictures
Sponsored Links
  #2  
Old 06-14-19, 02:00 PM
Member
Join Date: Oct 2016
Posts: 1,189
Upvotes Received: 26
Probably a faulty winding for that speed tap.
Check for proper voltage in cooling. If you have voltage swap two of the speed tap wires. If that fixes the problem change the motor.
 
  #3  
Old 06-14-19, 04:35 PM
Member
Thread Starter
Join Date: Jun 2019
Location: USA Los Angeles
Posts: 5
Thanks for the quick reply. I looked at the control board, and in the pic, all the way to the left, the last 4 pins are designated "circulator blower." I'm not a tech, so I am assuming you mean by speed tap, you are talking different voltages at these pins?!?!? I did see that all 3 wires in that area - HEAT, PARK, and PARK go straight to the motor. I never heard the blower spin at more than one specific RPM, but could I move the wire from HEAT to COOL and see what happens? COOL has nothing on it right now. It doesn't seem to call for "cool," when the AC is turned on. The light blinks as if it's calling for heat. The motor was replaced about 5 years ago, so it's newer than most other things. Forgive my ignorance, but automotive is my trade specialty.
 
  #4  
Old 06-14-19, 07:04 PM
Member
Thread Starter
Join Date: Jun 2019
Location: USA Los Angeles
Posts: 5
Hey, you were right. I tried moving the HEAT connector one space over to COOL, and I do get voltage there. I'm assuming I can use it like this, as long as I stay in cool mode only. I don't know why it used to work when it was on heat for both, and now it doesn't. The problems with the control board(s) started right after we had the motor replaced. For nearly 20 years, no problems. Then the bearings took a dump, and we needed a new motor. Shortly after that, the fan wouldn't shut off when it was in heat mode only, unless you unplugged it from the wall. So I replaced the control board and that fixed it for a short time. Then, the same exact problem again. Is it possible that this motor is screwing up the control boards with too much draw or something? Anyway, For the time being I do have AC again, and I did save the old control boards, so if the motor screws up the cool circuit, I have immediate replacements. Thanks for the correct and quick diagnosis. This is wonderful.
 
  #5  
Old 06-15-19, 07:36 AM
Member
Join Date: Jun 2018
Location: USA
Posts: 41
Upvotes Received: 1
You may not have a problem. There should be a motor speed tap on both the heat and cool positions on your circuit board. Generally heat is a lower speed and cooling is a higher speed. One of wires in the park position should be used. Post a pic of your furnace wiring diagram so we can figure out what speed(s) you are operating at.
 
  #6  
Old 06-15-19, 08:24 AM
Member
Thread Starter
Join Date: Jun 2019
Location: USA Los Angeles
Posts: 5
Thanks. The thought did cross my mind that logically, you would think that the board would energize the heat prong for heat, and the cool for cool. But I do distinctly remember thinking how odd it was that there was only a wire on heat, the first time I saw this. Right now, the wire is moved to cool, so I can use the AC. It was originally on heat, and no AC blower as mentioned. Maybe one of the "parks" belongs on heat or cool?

Name:  f1.jpg
Views: 30
Size:  50.9 KB
 

Last edited by PJmax; 06-15-19 at 08:30 AM. Reason: resized picture
  #7  
Old 06-15-19, 08:37 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,389
Upvotes Received: 208
Welcome to the forums.

All the pictures and diagrams you originally posted are only for the outside condenser.
I will remove the ones that aren't needed for this thread.

You have a three speed blower.
Black = high speed
Blue = medium speed
Red = low speed.

Park is just a place to keep unused wires so that they don't short out.
Keep the black on cooling and put the blue on heat.

The fan speed chosen for heat is usually selected by test measurements done when the furnace is installed. The blue wire on heat is a safe bet.
 
  #8  
Old 06-15-19, 09:33 AM
Member
Thread Starter
Join Date: Jun 2019
Location: USA Los Angeles
Posts: 5
OK, I appreciate this. Getting back to the premature failures in heat mode, where the blower was staying on after the thermostat tried to shut it off, could this be because the blue wire should have been used on heat all along? Is there more draw from black, or does that circuit function more as a relay or solenoid, and not have any real extra amp draw.
 
  #9  
Old 06-15-19, 11:22 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,389
Upvotes Received: 208
In heat mode..... the thermostat has no control over the blower. When the heat is called for..... it starts a timer in that board and that timer activates a relay to start the blower in heat mode. When the heat call ends.... the timer starts again and turns off the blower.

There are variations on these boards. On some activating the R to G terminal turns the fan on to the cool mode. This is the most common, While on others it turns the fan on to heat mode.

The relays on the board are the same size so what speed is connected to which terminal is not a concern. Quite possibly you had a limit control problem on your furnace. That would keep the blower running after the call for heat.
 
57TinkerMan voted this post as helpful.
Reply

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


Thread Tools
Search this Thread
Display Modes