Will a T-stat fix my problems.


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Old 08-26-11, 09:59 PM
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Will a T-stat fix my problems.

I have a couple of HVAC issues and I am not sure if they are related. I think they may be through the T-stat, but then again, I am no expert.

Here is a quick rundown of my HVAC system. I have a 3 heatzones; 2 t-stats upstairs, 1 t-stat downstairs. The upstairs t-stats operate an airhandler in the attic and a condensing unit outside. The downstairs t-stat operates an airhandler in the basement and a separate condensing unit outside. All t-stats/heat zones run off the same oil boiler in the basement.

Problem 1: The attic airhandler NEVER shuts off. In order to turn it off I have to open the breaker.

Problem 2: The condesing unit for the upstairs does not always turn on automatically or by operating the switch regardless of interior temperature. Sometimes I have to cycle the switch several times to get the condensing unit to come on. Tonight I could not get it to come on at all.

Both problems involve the "upstairs" systems and the only common link I can think of is the t-stat, although there are 2 independent t-stats that should operate this air handler and condensing unit.

The t-stats are older, so I was thinking about replacing them with programmable t-stats because even if they don't fix the problem they should save me money over the winter. If any knowlegible folks could provide me some insight into my problems and recommend some good, inexpensive, programmable t-stats I would really appreciate it. I have posted a link to my current t-stats below.

Thanks in advance for your time and consideration,
Mike

American Air Systems - Robertshaw 9500
 
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Old 08-27-11, 06:22 AM
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do you have a zone board or just a damper or two?
 
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Old 08-27-11, 05:27 PM
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I am not sure what a zone board is. I just know that I have 3 thermostats, 2 upstairs that run the same air handler and condenser unit. I believe that both T-stats can demand air and heat as required to their applicable portion of the house and they do actually keep the house different temperatures. For instance, the t-stat on the east end of my house (master bedroom) is typically kept at 70 in the winter because my wife is perpetually cold. While the t-stat on the west side of my house will typically keep that portion the set 66 in the winter.

I have also seen demand from the west side cause the condenser unit to trip on when that wing gets too hot, as programmed while the east side is still not at the set point.

I hope that helps.
 
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Old 08-28-11, 10:11 AM
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you would need a volt meter to troubleshoot the problem and you would need to find the zone control board. Usually near the air handler. The only way 2 stats can properly control 1 system is if they are zoned through the use of a zoning system.
 
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Old 09-11-11, 04:53 PM
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OK, I found my zone control board and I have a multimeter.

Here is a tech doc for my zone control board.

http://www.ewccontrols.com/acrobat/090375a0115.pdf

I have a 2 zone control board. It is model number EWC-ST-2E. There is a decent wiring diagram in the book, but here is a quick run down:

Zone 2 Tstat: I have W Y R wires.

Zone 1 Tstate: I have W Y R1 O B G wires.

I am sure that I am trying to find the 24V demand signal somewhere. Reading the manual it looks like the G wire controls the fan circuit, but I am not sure how to isolate the fault. If someone can tell me specifically where to stick my leads, I will be happy to post the voltages.

Thank you again for the help
 
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Old 09-11-11, 06:03 PM
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First, ensure the fan switch on zone 1 stat is in the auto position.



with the zone 1 stat fan switch on auto if you see 24v on the rt side screen then you need a new stat. If you have 0V on the rt side and 0V on the left side then it is the zone control or a bad relay in the air handler.

FYI - any replacement stat for zone 1 you purchase will need to have both a B and an O terminal.
 
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Old 09-13-11, 05:01 PM
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Well, I am getting like 50mV on both, so effectively, 0 both left and right. It looks like it is not the t-Stat. How hard is troubleshooting the relay or zone control board?

Strangely, the only voltage I found on the board was 10V at the zone1 and zone2 motors.

Thanks again for the help thus far.
 
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Old 09-13-11, 05:12 PM
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are you checking AC or DC..... should be AC.........
 
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Old 09-14-11, 04:25 AM
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I am an idiot, I was checking DC last night. I thought it was a 24VDC circuit, but since their is no rectifier that doesn't make any sense. I will check it on AC when I get home tonight and post results. Thanks again.
 
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Old 09-16-11, 07:31 AM
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First I want to say thank you so much for the time so far. I really appreciate it. I am pretty hand and engineering savvy, I am just not familiar with the systems. Your expertise is empowering me to save some money, but more importantly understand the systems operating in my house.

That said, I have my AC results now and they are not quite what I expected. On the demand (right) side, I got 7 volts (actually 6.87V). On the left side I got 24V (actually 28.6V). I checked, and double checked and triple checked my test connection points and the connectivity. I am convinced that those are accurate voltages as I am using a brand new, high quality clamp on ammeter/multimeter.

So is 6.87V enough to energize the relays? Is this indicative of a T-Stat short or something? In any case, I am hoping it is a bad T-Stat as I was planning on replacing my digital T-stat with a new programmable t-stat. If I do need a new t-stat could you recommend a low-cost programmable that meets my requirements? I would like to be able to turn the heat down automatically at night and while everyone is out for the day. I have heard that this could save me a lot of money on my energy bills.

Like I said, I have 2 condensing units, 3 tstats (would need 2 zone controlling "master" t-stats) and a "subordinate" tstat that goes into the zone 2 on my zone control board. Thanks again.
 
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Old 09-16-11, 07:39 AM
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Sorry...I can't answer the question...the Pro's will be around later I'm sure...

But I'm curious about the Member name? I'm guessing CWO to LDO?
 
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Old 09-16-11, 02:00 PM
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E-7 Marines to O-1 Navy about 5 years ago.
 
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Old 09-16-11, 02:06 PM
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Got cha...that was my other guess...lol. I was thinking maybe a WO weapons officer which we always called a Gunny or Guns as well Thx....

Boy, that had to have been an adjustment...24 yrs Navy (CPO) here.
 
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Old 09-17-11, 06:23 AM
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just to verify you had 24V on the left side between R & G. This would indicate that the relay in the air handler is stuck closed. Just to verify this remove the G wire from the zone board. Does this shut the blower off? If it does not shut off the blower then it is the relay in the air handler.
 
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Old 09-17-11, 08:36 PM
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Originally Posted by hvactechfw
just to verify you had 24V on the left side between R & G. This would indicate that the relay in the air handler is stuck closed. Just to verify this remove the G wire from the zone board. Does this shut the blower off? If it does not shut off the blower then it is the relay in the air handler.
Thanks, Ill give it a shot.
 
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Old 09-17-11, 08:53 PM
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Originally Posted by hvactechfw
just to verify you had 24V on the left side between R & G. This would indicate that the relay in the air handler is stuck closed. Just to verify this remove the G wire from the zone board. Does this shut the blower off? If it does not shut off the blower then it is the relay in the air handler.
OK, pulled the Left side green wire and the air handler still kicked on. Pulled the Right side and stayed on as well. Sounds like a stuck relay. I guess I will start researching that. As far as replacing my t-Stats, I am still thinking about doing that. Any suggestions for inexpensive programmables?
 
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Old 09-18-11, 05:35 AM
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Honeywell TH4110D would be my personal choice. Remember that zone 1 stat must have both a B and an O terminal not an O/B terminal. These Honeywell stast have separate terminals as needed on zone 1.
 
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Old 09-18-11, 09:19 AM
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Alright, opened up the airhandler and it looks like my relay is a

9400-13Q101. At least that is what I read off the label of the existing relay. There were several little black boxes and the schematic was a little tricky to read:

-one transformer (120V-24V)
-the thing I think is the relay (9400-13Q101)
-something else that was not exactly clear from the schematic... I think it was an optional install for a cabinet interlock switch preventing running the AH while the cabinet door is unistalled

Here is a link to the relay page:

http://relays.te.com/datasheets/9400_Series.pdf

Does this make sense? Is the replacement a "simple" wire to wire swap with the 10 or so wires installed? Kind of like changing the distributor cap on an old car, label the leads, label the terminals take out the old, put in the new (in exactly the same spot) then move on with your life?

I found this one on line:

Surplus City Liquidators

Not sure if it is the right one. $5.00 seems pretty cheap, saw it on one website for 188.12 which seems ridiculous for a little relay. I was expecting $30-40.
 
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Old 09-18-11, 07:31 PM
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the link to the relay page is not good. However, the other link to the relay is. The price sounds right, nothing special just a 24V DPDT relay. Should be a simple swap.
 
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Old 09-21-11, 09:11 PM
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Man, I can't buy a break on this relay. The place I was looking at online turned out to not have it in stock, and I haven't been able to find an exact parts match on line for what I think the serial number is: 9400-13q1, my question is can I use any 9400 series relay and modify the box to make the mounting work? Or do you know where you can get the part I need.

I did see some places that I can only assume are price gouging because they are selling that relay for 140.00.

Thanks again,
mike
 
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Old 09-22-11, 04:23 AM
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do a google search for this : PR380 Fan Relay

It is the the same relay different manufacturer.
 
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Old 09-26-11, 04:11 PM
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Got the relay in the mail today. Installed it within 5 minutes. Tested satisfactory. Strange thing is that I ran the voltages with the new relay and it was I got 7VAC from Green to C. on the right side. Not what I was expecting but the system works correctly (as far as I can tell).

Thanks again, you probably saved me 200.00 on this.
 
 

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