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A/c won't shut off unless we turn the system off - honeywell pc8900

A/c won't shut off unless we turn the system off - honeywell pc8900

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  #1  
Old 07-06-14, 09:32 PM
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A/c won't shut off unless we turn the system off - honeywell pc8900

Howdy, new member. I posted in another thread, but our unit will no stop blowing a/c unless we physically turn off the system at the thermostat.

It is a pc8900 honeywell. If I just replace the thermostat with another pc8900 wall unit should that do the trick? Or do I have a different problem?

Thanks,
Boomhaur
 
  #2  
Old 07-06-14, 10:10 PM
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It could just as likely be the module (EIM counterpart).

I recommend a Prestige IAQ.

A Redlink VisionPro 8000 and a separate EIM would be a less expensive alternative.
 
  #3  
Old 06-11-16, 06:11 PM
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PC8900A - wont turn off until manually shut off

I have a similar issue. AC wont turn off until I manually shut it off. I have two thermostat, one upstairs and one downstairs. The upstairs one is controlling the system fine though. Could it be transformer or Thermostat?
 
  #4  
Old 06-11-16, 06:48 PM
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Welcome to the forums.

You have two systems or one primary stat and one aux. stat ?
There can't be two full function stats.
 
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Old 06-11-16, 08:55 PM
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PC8900A - wont turn off until manually shut off

Thank you.

Sorry - I do not know about the configuration of my a/c system. How can I be sure or identify it. When the t-stat upstairs is working, I don't think air is blowing out of the vents downstairs.

I just have one condenser so my t-stats must be one primary and one aux. How is this supposed to work?
 
  #6  
Old 06-11-16, 11:43 PM
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A very common cause for this issue when 2 thermostats control a single system is a stuck motorized zone damper.
 
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Old 06-12-16, 09:07 PM
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Thank you. Is there any tests I can do to confirm that the zone1 damper is an issue? I went to attic today and saw I have Honeywell communication module and Honeywell Mini-Zone system (there are two zones). What is the function of this motorized zone damper?
 
  #8  
Old 06-12-16, 10:55 PM
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The damper should be open when the system is off (in most applications) or that zone has a demand . This is power closed / spring open.



I drill a hole on each side of it and measure the static pressure with a manometer.

I also give the working zone a demand and remove one wire nut connection to that stuck damper to see if it opens and closes.

Sometimes it is only some insulation on the large set screw preventing the damper from opening but it is usually a damper that requires replacement.
 
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Old 06-13-16, 09:33 PM
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Thanks. So, in my case, damper for zone1 (downstairs) should be stuck open or closed? Just curious.
 
  #10  
Old 06-14-16, 06:47 AM
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Sounds like it might be stuck open.
If the zone 2 has a demand and zone 1 is stuck open, zone 1 would get air too.

It could be as simple as a broken wire connection if you are lucky.

Measure for 24 volts AC to the damper if it should be closed.
 
  #11  
Old 06-14-16, 03:26 PM
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Pc8900a

I do not think I am getting as much of air as I would when Zone 1 thermostat is ON versus when it is off and Zone2 is cooling.

When Damper is closed what would be the voltage vs when it is open? Where do I measure this ac voltage, can you tell me per the wiring below?
 
  #12  
Old 06-14-16, 03:53 PM
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24vac should be present between M1 and M6 when the damper should be closed.

If power checks out at these terminals correctly you can move on to the damper itself.

The damper usually has a set screw that moves to the Open and Closed stickers on the damper when power is applied or removed. 10:00 to 12:00 is what I remember in a left to right application is what I would expect.

It is easier to see the set screw move if you create a demand in the other zone, remove demand in zone 1. This will supply 24 vac to your damper. You can then disconnect a wire nut connection at the damper end to see if it moves.
 
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Old 06-15-16, 11:14 PM
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Please bear with me as I am new DIYer and do not know much about HVAC configuration. Why would you think damper is an issue here when my a/c would continue cooling even when the cool point temperature has already been reached and well below. Does damper provide feedback regarding its open/close position to Minizone panel which shuts the system off? If it is not a closed system, I am not getting why stuck-open damper would cause my a/c to run continuously even when the set cool point has been reached and room is well below that temperature. Just trying to understand the fundamentals here. Thanks for your patience and help.
 
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Old 06-16-16, 06:48 AM
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It could be a damper issue if the other zone has a demand.
 
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Old 06-16-16, 10:40 AM
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Hello. Can you please explain why it could be a damper issue if other zone has demand?

Even if zone 2 thermostat is shutoff and there is no demand on zone 2. My AC runs continuously when zone 1 thermostat is on, set cooling point has been reached and temperature displayed is well below it.
 

Last edited by sghimire; 06-16-16 at 10:44 AM. Reason: Typo
  #16  
Old 06-16-16, 01:31 PM
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Sounds like you have proven that it is not just a stuck damper
 
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Old 06-16-16, 05:30 PM
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Yes. I was wondering my thermostat at Zone1 is an issue. How can I test PC8900A thermostat?
 
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Old 06-16-16, 06:21 PM
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Disconnect zone 1 Y and G at the zone control board.
 
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Old 06-16-16, 09:31 PM
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Disconnect and then what test should I do to confirm thermostat is faulty
 
  #20  
Old 06-17-16, 03:28 PM
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Also what would be the good replacement Thermostat for PC8900A?
 
  #21  
Old 06-17-16, 08:21 PM
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Y = compressor
G = fan
W = heat
R = 24 volt power

If you disconnect zone 1 Y and G and turn off zone 2 stat the system should turn off.

The number of conductors between the EIM and zone 1 thermostat would help in recommending a replacement.

I assume that you have at least 4 but a 5th conductor would allow a greater number of replacement options.
 
  #22  
Old 06-17-16, 08:34 PM
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Thanks. Yes, I have 4 wires, R, W Y and G. What thermostat can I use. the module it is connected to is W8900A1046. When I disconnected the thermostat from wall plate at zone 1 while there was demand at zone 1, system was off. It could be thermostat in my mind.What do you think?
 
  #23  
Old 06-17-16, 08:49 PM
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I think the thermostat terminals are numbered with that model.

If you only have 4 conductors I would use a Honeywell VisionPro TH8110R.

EIM's open the door for more stages of operation but it sounds like you may have 1 stage heat / 1 stage cooling.
 
  #24  
Old 06-17-16, 08:56 PM
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Thank you. How do I confirm stages of heating cooling I have.
 
  #25  
Old 06-17-16, 09:07 PM
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Do you have a wire on the EIM Y2 or W2?

Wires on Hum or VNT?
 
  #26  
Old 06-18-16, 09:36 PM
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HUM (top one), RH and R are Jumpered at communicating module and connected to R at Zone1 Mini-zone panel. Hum (Bottom) has Yellow wire connected.

VNT do not have wires.

W1 has white wire connected.
W2 does not have wire connected.

I have this Fresh Air Ventilation Module but is turned off ( I believe it is not used).

BTW, I did remove the Y and G wire from Mini-Zone panel's Zone 1 and system shut off, although it took about 2, 3 minutes after I removed the wires.
 
  #27  
Old 06-18-16, 10:13 PM
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Single stage of heat and a humidifier. Does the humidifier function?

Do you have a wire on Y2 ? (stage 2 cooling)
 
  #28  
Old 06-19-16, 08:04 AM
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Here is the wiring. I do not see Y2 terminal. I think this terminal is not used. Will Honeywell TH8110R1008 Vision Pro 8000 Touch Screen Single Stage Thermostat with Red Link Technology work for my system? How do I confirm if humidifier is functioning? Where is this unit?

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Last edited by sghimire; 06-19-16 at 08:14 AM. Reason: More information.
  #29  
Old 06-19-16, 11:16 AM
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How many conductors on the 1234 wire ?

6 would be great. It might allow for the Honeywell TH8321R to support your setup.

The TH8321R would also work with a Redlink EIM. You could get away with using only 2 wires.
 
  #30  
Old 06-19-16, 12:40 PM
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5 wires but blue one is not used. You did not answer how I confirm if humidifier is there and functioning.

Which tstat do you suggest? I want to replace it asap. Thanks for your help.
 
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Old 06-19-16, 12:43 PM
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At this time I do not plan to change EIM. But would like to buy tstat that would support newer EIM in case I want to change it in the future.
 
  #32  
Old 06-19-16, 01:37 PM
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The EIM that you have will not support any thermostat available today. It must go if the thermostat is going.

The Honeywell TH8321R is a great option because it can be used to replace a 4 wire thermostat if you use batteries. It can be used as a 5 stat if you have the extra wire available. This will save you money on batteries. It can also support a humidifier and more stages of heating and cooling if want to pull wire or have

If you add the optional Redlink EIM the TH8321R it can control 2 stage heat and 2 stage cool and a humidifier and vent damper and a dehumidifier using only 2 wires between the stat and EIM.

The TH8321R can also be used wirelessly when it has the Redlink EIM.

The TH8110R will not support humidity control.

The Honeywell Prestige IAQ would be a step up from a TH8321R and an EIM.
 
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Old 06-19-16, 03:29 PM
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Oops.

Thanks for the info. Can you please let me know details of the wiring for the new thermostat/EIM you've suggested in my current config.

Is it just removing the existing wiring from existing EIM and connecting it to Redlink system? If that's the case probably I can do it myself. Do I need to change the Mini-Zone panel as well or not?

Fundamental question still remains: is it really thermostat? Just would like to know your opinion based on what I am seeing...

Thanks again for the great support!!!!
 
  #34  
Old 06-19-16, 04:17 PM
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It sounds like you have proven that it is the thermostat.

The mini zone control seems to be working so it can stay.

A humidifier looks like the back of an old 19 inch television. It will have a drain and it will have a small pipe feeding it domestic water. It will also have 2 wires running to the existing EIM.

If it has been abandoned you can use one of many Honeywell thermostats but I would choose the TH8321R since you have the option to control a humidifier or add an EIM.

That stat is around $130 and the EIM is around $45.

It will connect very much like the existing EIM but instead of using 1234 you would use R and C between the stat and EIM.

I wish that I could see a little further left. If the 1234 bundle of wires also has a brown and blue you can omit the EIM and save $45.
 
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Old 06-19-16, 08:31 PM
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Here is a picture I took to show little further left of 1234 bundle of wire. It has blue, but no brown.

Just to confirm I need to buy the following correct:
1. Honeywell TH8321R1001 Vision pro 8000 Thermostat
2. Honeywell THM5421R1021 IAQ Equipment Interface Module

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  #36  
Old 06-19-16, 10:23 PM
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Yes, those model numbers look good.
Looks like that would be close to 145 buck plus 50 bucks.

The Honeywell Prestige IAQ kit is $230.

You can shop around for pricing but I am an Amazon shopper unless it is available at a better price at a big box store.

Those would be your two best options. I chose the Prestige IAQ for my home. It has a color screen gives you data logging and delta tee alerts.
 
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Old 06-19-16, 10:34 PM
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Okay. I will check Prestige IAQ too. I believe EIM is same, correct? My next challenge would be to correctly connect these wirings from the existing EIM. Can you help me explain me how my existing wiring will map to new EIM.

Also, I did not find humidifier unit, I am not sure if wiring is there without unit itself.
 
  #38  
Old 06-19-16, 10:45 PM
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Yes, they have the same EIM.


If you do not have a humidifier you can get away with a TH8110R or TH8321R stat and no EIM. The TH8321R gives you humidity display, the ability to over cool by 1, 2, or 3 degrees if the humidity is too high in your home.


I don't have a humidifier or a multistage system but I love the Prestige IAQ kit. After installing a few dozen of them I had to get one for my home.
I have a pressure switch, a float switch, 2 duct sensors, and a wireless outdoor sensor connected to my Prestige IAQ kit.

Where does the HUM wire go from the existing EIM?
 
  #39  
Old 06-20-16, 09:20 PM
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The top HUM connection is jumpered with Rh and R and goes to red wire (#1) on Minizone panel @ Zone1.
The bottom HUM connection goes to Y1 on the right side which then goes to Yellow wire (#3) on MiniZone Panel @ Zone 1.

Does IAQ kit comes with wireless sensor. Do you have link to Amazon website so I know what kit you are talking about?
 
  #40  
Old 06-21-16, 06:26 AM
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https://www.amazon.com/gp/aw/s/ref=is_s?k=prestige+iaq

The first line has an outdoor sensor.
 
 

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