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Help setting up the Venstar ColorTouch T7900 thermostat with Rc and Rh using a r

Help setting up the Venstar ColorTouch T7900 thermostat with Rc and Rh using a r


  #41  
Old 03-22-22, 08:55 PM
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No.... they can float or be mounted. The flange is only for mounting.
 
  #42  
Old 03-26-22, 06:01 PM
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I'm still waiting for all the parts to arrive, but I was thinking of the Fan (G) connection and how with the current diagram, I can only control the evaporative cooler's fan individually.

Although not completely needed, I would like to be able to control both the evaporative cooler's fan and the furnace's fan.

My logic for wanting this is as follows:

The thermostat has four options: Heat, Cool, Auto, or Off.

Keep in mind, this thermostat also has a 'Fan Mode' option that can be enabled which I use quite commonly.



I know that the furnace will control the fan itself if it is on, but I would also like to be able to manually turn on the furnace fan without turning on the actual furnace.


It would be nice to be able to circulate the indoor air (Furnace G) by using the furnace blower when the 'Heat' option is selected and 'Fan Mode' is on. But the thermostat is turned down enough so that the actual furnace does not activate (just the indoor furnace fan stays on). This helps with keeping the indoor air from getting stale and helps keep the hot/cold air circulating throughout the house.

On the other hand, at different times of the year, it would also be nice to be able to bring some outdoor air inside using the evaporative coolers fan (Cooler G) when 'Fan Mode' mode is activated and the Cooler option is selected.

Would it be possible to add a third relay so that when the Heat option is enabled, I have the option of using the furnace's fan, and when the Cool option is enabled, I can use the evaporative cooler's fan?
 
  #43  
Old 03-26-22, 06:45 PM
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If you need the thermostat to control the evap cooler...... how can it do both ?
It can only turn both blowers on at the same time. (with a relay)
You don't have the ability to control two blowers independently with one control.
 
  #44  
Old 03-26-22, 07:32 PM
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I see what you mean..

Okay, so the furnace fan cannot be controlled directly from the thermostat since it's already being used for the cooler, but perhaps I can still have control of it through a round-about method.

I have an idea: would this work?

I could get either a Z-Wave or Zigbee switch and connect it to the R and G of the furnace. I could then remotely turn on/off the furnace fan wirelessly using Home Assistant.



Would something like that be possible?
 
  #45  
Old 03-26-22, 08:01 PM
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Sure. A remote controlled switch would work. Just make sure the switch uses a relay.
 
  #46  
Old 04-02-22, 08:46 PM
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Everything I ordered has now come in (including my replacement White-Rodgers). Time to get started.

 
  #47  
Old 04-03-22, 12:22 AM
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So I wired it up exactly as you said, but it's not working correctly. The evaporative cooler is working as expected, but the heater is not working correctly. The heater stays on even if I turn it off through the thermostat. Do you have any ideas as to what may be causing that to happen?

Also, the relays get REALLY hot, is that normal?
 
  #48  
Old 04-03-22, 09:52 AM
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What are you using for the Z-wave or ZigBee switch? How do you have it wired to your G terminal? My concern here is that you are sending 120VAC between G and R.

The relays should not be super hot.

Do you have a voltmeter?
 
  #49  
Old 04-03-22, 10:28 AM
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So far I haven't even added any ZigBee or Z-Wave switchs to the system. So far I've got it wired up like post #26 detailed.
 
  #50  
Old 04-03-22, 11:27 AM
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You need to determine what is holding the furnace active.
Disconnect one wire from the stat to each relay. Does it stop now ?
If yes... is it just one relay causing the problem.

Measure the voltage to the relays. You started this project a long time ago but I'm just now remembering that the w/r controller is DC as there are three rectifier diodes. The voltage may be too high.

Measure the AC and DC voltage to the relays.
 
  #51  
Old 04-03-22, 06:03 PM
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Okay, so here's what I've found out. If I just turn on the cooler, it will turn on and off without issue and the furnace does not engage. Also, the relays don't become hot when the system is idle or when the cooler is turned on. However, once I turn up the heat and the furnace turns on, there is no turning it off using the thermostat. Here is how the relay's read when either the system is idle or when the cooler is on:

Now once I turn up the heat and the thermostat turns on the furnace, both relays begin to get quite hot to the touch. The relays also make a faint buzzing noise. Turning off the thermostat does not turn off the furnace. The reading from the relays seem to remain the same both when the thermostat turns on the furnace and when the thermostat is idle (after having turned on the heat and then back off). Here are those readings:



 
  #52  
Old 04-03-22, 08:27 PM
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I just tested the disconnecting a wire from the relays and here's what I found. If the thermostat is on stage 2 heating, I can disconnect a wire from W2 and 2nd stage heating will immediately disable and the furnace will kick down into stage 1 (but not off). If I reconnect the wire from W2 the furnace immediately kicks back into stage 2. The only way to get the furnace to power off is to disconnect a wire from both relays. The wire I disconnected is shown below:


Once I disconnect the wires, I can plug them both back in and the furnace stays off until I tell the thermostat to turn it back on. It's like there's something preventing the relays from switching off once they are turned on.
 
  #53  
Old 04-04-22, 04:50 PM
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Should I try purchasing a different relay, or is there something else that I can try doing? The thermostat almost works perfectly. The cooler works great and the heater turns on and will engage stages 1 and 2 without issue, but it just won't turn off.
 
  #54  
Old 04-04-22, 07:40 PM
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Pictures aren't necessary. You didn't label the terminals in your pictures.

The relays have two coil terminals and two switch contacts.
When the relay is idle.... there should be whatever voltage the furnace uses to switch on the switch contacts. We're not really concerned with the switch side.
It would be normal for the furnace to run with power on to either relay.

I'm assuming the AC 10.48 /DC 17.30 is on the coil side of the relay. There is a high DC component because of the diodes in the W/R unit. Some hum is normal with most relays. I'm guessing it's the DC component that is causing the relays to run hot. You may need to switch over to a DC relay. A 24vdc N.O. relay would work.
 
  #55  
Old 04-05-22, 08:47 PM
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Would you suggest I purchase 2 of these?
 
  #56  
Old 04-05-22, 08:57 PM
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They're a little expensive for what is required.

I usually try to stay with a name brand item but this relay package looks perfect. It comes with its own internal filtering so the relays won't chatter. I'd give it a try. It's two relays in one package.
AC/DC 24v dual relay

 
  #57  
Old 04-06-22, 04:14 PM
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Awesome, I'll give that a try. I ordered it this morning and it says it'll be here tomorrow. I may not like Amazon, but I love to use them as they are so convenient. Next-day delivery? Jeesh, their logistics are on point! Anyway, I wanted to mention something else.

I went on the roof today to change out the evaporative cooler's pads (a yearly headache) and I noticed that the pump does not turn off even though the thermostat is turning off the fans for the cooler. I didn't even notice until I went on the roof since the pump is silent.

I'm thinking, and please correct me if I'm wrong, that the pump not turning off and the relays not working correctly for the heater could be fixed by simply converting the DC power to AC power. Is there any way to easily convert that DC power to AC power?

It was this post and this post that sparked my questioning of the AC/DC power issue. Is there a way to just convert that DC power to AC power?
 
  #58  
Old 04-07-22, 11:30 AM
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The AC/DC 24v dual relay that you suggested came first thing this morning and I have it installed. It's working perfectly! The heater now switches off when it's told to by the thermostat and both heating stages work. This is so exciting! Thank you so much for the help, PJmax. Almost everything is working now. The only remaining thing that is not working correctly is that the pump does not turn off when the thermostat turns off the cooler, even though the thermostat turns off the fans without issue.

I have the cooler wired slightly differently though than what you mentioned in post #24. When I only connected the Y >> Y1, only the fans would turn on and the pump would not engage. But, when I connected Y >> Y2 and W >> Y1, the pump engages without issue and the fans turn on and off, but the pump stays on forever (once the cooler is activated).

Once again, it seems like something is preventing the thermostat from turning off the pump (perhaps the DC power)? If I restart the thermostat, the pump will shut off and stay off, but once I turn on the cooler, the thermostat will turn on the pumps forever even if the cooler is later turned off. The only way I know of getting the pumps to turn off is to restart the thermostat again.

Do you have any ideas on how this could be fixed? It's not really that big of a deal, but it's just the final piece of getting everything working 100%.
 
  #59  
Old 04-07-22, 09:10 PM
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The W/R controller was built using DC and that's what it's relays are. No real way to convert it .
You can convert AC to DC but not the other way around.

I don't know how that thermostat switches. If it's electronic.... it uses AC switching. If not... it uses relays.
When the stat activates.... does it click when the functions change ?
If not.... then it is electronic and the DC may be holding it active.

Do you have any diodes hanging around ?
Type is absolutely not critical. Try it in the W/pump line. Not sure which polarity.
It may work in one direction and not in the other. Try both ways.
Feel free to yank a diode from something electronic and scrap.

 
  #60  
Old 04-07-22, 11:08 PM
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It's definitely an electronic thermostat then as I don't hear any clicking whatsoever when the thermostat activates. It's completely silent. I don't have any diodes lying around, but I can order some.

Since I'm going to get some diodes, I figure I should order a pack of several different kinds so I have some for the future to play around with. Would these work? Or would you recommend a pack of something different?

Before COVID-19 happened I was going to school for my electrical engineering degree. I had just completed my first 2 years of prerequisite classes (which had nothing to do with electrical engineering) and was ready to take my first electrical engineering class. Unfortunately, I never did get the chance to take my first electrical engineering class as COVID happened and it likely won't be for a few years until I can go back and finish my final 2 years to get my degree.

I guess what I'm trying to say is that I don't mind getting into the nitty and gritty details. Heck, as we've been going through this, I've watched countless youtube videos and several Khan Academy videos. I may not always understand why we're doing something, but I follow your guidance as we go through this. I honestly find this quite a fun hobby as I work to learn how everything works.

If it turns out the W/R controller just won't work, I wouldn't mind trying to build my own controller from scratch if that's what needs to happen. Either way, this has been quite the adventure and I've been enjoying it every step of the way.
 

Last edited by Vanimox; 04-08-22 at 02:05 AM.
  #61  
Old 04-09-22, 08:59 PM
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Turns out there are additional issues with the setup using the soldered common line we attached and I believe it's all related to the DC current. The transformer on the w/r makes a buzzing sound and gets very hot when the common wire is connected to the thermostat; however, if I disconnect the soldered 24vDC common wire we added, it makes a very faint (almost inaudible sound) with a very slight warmth which I believe is the way it's supposed to behave.

Additionally, after having spent more time with the thermostat changing the cooler from stage 1 to stage 2, it appears that I can select stage 1 and I can hear a click from the w/r which must be the relay clicking which is great (the thermostat makes no clicking so it must be using electronic switching). Stage 1 cooling works great at this point which is perfect. Now I can turn down the thermostat to activate stage 2 cooling. When the thermostat shows stage 2, I also hear a click from the w/r indicating that its relays are working as intended. Stage 2 cooling also activates perfectly at this stage. Now is where the issue lies. If I turn up the thermostat to go back to stage 1, the thermostat will say on the display that it's going to stage 1 cooling, but I hear no click from the w/r and the high cooler fan speed stays the same indicating that the w/r is stuck in stage 2 cooling. I believe the 24vDC current is what's affecting the switching from stage 2 cooling to stage 1 cooling. This is in addition to the pump never deactivating even when the cooler is fully turned off from the thermostat.

I've got this 24vAC adapter. Can I just use this instead of using the w/r's 24vDC current? I'll just disconnect our soldered line and instead connect this adapter to the setup.

I know you said in the past that the 24vAC has to come from the cooler's side, but if it's just a continuous 24vAC current, why would it matter where it came from? I figure it wouldn't hurt to try using this 24vAC adapter. Worst case scenario, it just won't work. But how could I connect this adapter to the current setup?

I've laid out the current setup and drawn a red X through the 24vDC wire where I will disconnect it. I've also attached the 24vAC adapter with pink lines in the diagram. If I attach the 24vAC line to where I disconnected the 24vDC line, where do I connect the other wire to complete the circuit?


 
  #62  
Old 04-10-22, 10:00 AM
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What if you swapped how you power your thermostat? In other words - power the thermostat from the gas furnace, use relays on the evap cooler side.

Might be able to do it with the relays you have already purchased. Or use a different setup.

Some reference materials: 8-wire 120v Honeywell conversion to 24v NEST Learning

https://bravocontrols.com/shop/mecha...ng-and-4-gang/
 
  #63  
Old 04-10-22, 01:11 PM
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You can't power the stat with ext 24vac and then electronically switch DC loads.

You could use the furnace for stat power.
Then you would not need that relay pack for the furnace.

You would then need to isolate between the stat and the W/R unit.
If you must have Y, Y1 and G then you'll need three relays to go in that direction.
If you can use two..... then that relay pack would be fine.

Why can't the pump and blower come on together ?
 
  #64  
Old 04-10-22, 07:22 PM
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Thank you caddymac for the idea of powering the thermostat from the gas furnace and then using relays on the evaporative cooler's side. I did exactly that, and everything seemed to be working perfectly except that the fan from the cooler's side (stage 1 and stage 2) would not turn on. The w/r pump turned on and off just as it should, the 2 heat stages worked without issue, but the fan for the cooler wouldn't turn on at all.

Even though the fans for the cooler would not engage, I could hear the relays clicking each time I changed the thermostat from just energizing G, to G and Y1, to G, Y1, and Y2. After some more fiddling, it appeared that I could manually connect the Rc wire (which was not plugged into the thermostat) to the G wire and get the fans to come on, but if I put the Rc wire into the thermostat instead of the Rh wire, it would not power the thermostat (I assume because the common wire from the heater didn't have a completed circuit).

I then figured that since the Rh wire only needs to be connected to the furnace to complete the C wire coming from the furnace for thermostat power, and the Rc wire only needs to be connected to energize the G wire: "what if I just shove them both in the same R terminal in the thermostat"? It felt wrong, but at the same time, I had been playing with these wires for 2-3 hours at this point and was getting tired so I was in a "let's just do it and see what happens" mindset.

Well... it worked. Everything works. Literally, everything is working.

The pump turns on and off, the fan for the evaporative cooler works, the 2 heat stages work, the 2 cooling stages work, and the White Rodger's transformer is no longer overheating nor making a really loud buzzing sound.

I'm going to work on making a diagram in the next day or two to post so I can show exactly what I did and get some feedback since connecting the Rc and Rh seems wrong and didn't seem like it should work (but it did).

Also, thank you PJmax for telling me to put that 1A Fuse with my common wire installation. As I was playing with the wiring today, I accidentally touched the R and C wires together while trying to connect a different series of wires and blew the fuse instead of the w/r. Thank you for telling me to put that fuse in there!


Caddymac, I'm going to order that 8-gang relay board that you mentioned because I think I'm going to need it to complete this endeavor.

Even though the thermostat is now working perfectly, there's still an issue that I would like to automate if at all possible:

There are two dampers that are supposed to be opened or closed based on whether the evaporative cooler is running or whether the furnace is running. If the evaporative cooler is running, the vent on the roof connecting the cooler to the indoor ductwork is to be opened and the furnace vent is to be closed. On the other hand, if the furnace is on, the evaporative cooler's vent on the roof is to be closed and the vent connecting the furnace to the house's ductwork is to be opened.

I would like to install auto-opening/closing dampers and tie them to the thermostat using relays if something like that might be possible. Would that Mechanical Relay Board work for something like that?
 

Last edited by Vanimox; 04-10-22 at 07:45 PM.
  #65  
Old 04-13-22, 07:01 PM
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Here's the diagram. What do you all think? Is there anything that should be changed? It's working perfectly, but I want to make sure everything also looks safe.


 

Last edited by Vanimox; 04-13-22 at 07:29 PM.
  #66  
Old 04-14-22, 10:25 AM
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You shouldn't be mixing the R from both the cooling and heating systems. The reason why your fan (G) isn't working correctly and needs the R from the cooling side is the circuit isn't complete. To fix, you need a 3rd relay for the purposes of the fan.
 
  #67  
Old 04-14-22, 10:42 AM
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Exactly... I had mentioned three relays previously.
Remove the red/R jumper from the stat to the dual relay module.
The relays R source is coming from the W/R control.... not the stat.
 
  #68  
Old 04-15-22, 09:23 PM
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Could you help me map how I should change my current configuration and link me to which additional relay I should buy? I'm really confused about what I need to change. Also, should I purchase that 8-gang relay that Caddymac recommended? Also, keep in mind that later this year (or next year) I would like to add those auto-open/closing dampers into my system. Those dampers work using 24VAC so it should have no issues being incorporated into the system we're setting up.

Thank you both again for your help, I can't believe we've made it this far. I feel like we're almost at the finish line!
 
  #69  
Old 05-06-22, 07:15 PM
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It's been several weeks now and it's been working great, but I would like to add that third relay if you think it's safer. Any ideas?
 
  #70  
Old 05-13-22, 07:20 PM
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Still here... Bumping this thread for visibility.
 
  #71  
Old 05-13-22, 11:57 PM
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So the red R wires are still combined ?
If it's working ok and nothing is running hot.... leave it.

What would I personally do.... use a relay.
The reason is the R coming from the W/R controller is not true AC and not even 24v.
The R coming from the furnace is pure AC at 24v.
 
 

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