Wiring for Replacement of Robertshaw 300-208 by Honeywell RTH8500D

[Robert T.]

Hi.

I have a heat pump and an electric heat system and I am trying to replace my old thermostat (Robertshaw 300-208) with a Honeywell RTH8500D.

The original wiring setup on the Robertshaw 300-208 was the following:

terminal - color

---------------------------- W1 - white Y1 - yellow G - green R - red

24V - jumper to R 24V(c) - black O - orange B - not connected

I have made the following connections on the Honeywell RTH8500D:

terminal - color

---------------------------- RC - jumper to R R - red O/B - orange Y - yellow G - green C - black E - jumper to AUX AUX - white

This wiring scenario seems to be working ok for a while, but after some time the circuit breaker turns off and I have to reset it. I have tried other wiring scenarios as per the manual without success, but I have to admit that it's pretty difficult for me to understand.

I would welcome any help to resolve this issue and the Honeywell site and their client service is of no use.

Thank you.

[Don Y]

The "classic"/legacy labeling is: W1 commands heat Y1 commands cooling Rh & Rc are the 24V "hot" supplies for heat and cool, respectively. C is the 24V "common" (I hesitate to say "ground") G commands the fan/blower O & B change the "direction" of a heat pump (cooling & heating, respectively)

The colors *typically* used are rather intuitive: White, Yellow, Red, Common is brown/black/blue -- depends on "what's left over" in the cable, Green or Grey, Orange and Brown (!!) There's no guarantee that the original installer followed this convention, though... In your original case, it does *appear* to be the case -- assuming the other ends of the wires are connected appropriately (just because he used the right colors doesn't mean he wired them to the right actuators!)

The Homelywell appears to be rational in its labeling. But I wonder why white (heat) is relegated to E/AUX??

I suspect your tstat is wired more or less correctly and the breaker tripping is an unrelated issue. Presumably, the circuit breaker that you are referencing is the (large) breaker that supplies "heating power" to your system (?). Are you sure the loads aren't wonked?? I.e., that the breaker isn't actually doing what it is supposed to do -- protecting you from something that's not as it

*should* be?

Are you sure the breaker isn't fatigued and tripping at a lower than expected point?

Without an ammeter, the only practical way of determining the actual load placed on the electrics is to monitor your KWHr meter with everything OFF except the heat. You can then determine the rate of power consumption which translates into amperage -- which you can then compare to the marking on the breaker.

[For most folks, this is too tedious an exercise to "get right"]

Can you isolate portions of the heater "load" to determine if one section is possibly failing? (this assumes the breaker is not the problem)

[trader_4]

I don't have experience with heat pump based systems. But from what I can see, I agree with most of your analysis. The only way I can see that miswiring a thermostat could cause an AC supply breaker to trip would be if it somehow resulted in the heat pump stopping, then restarting immediately without a 5 min rest period, putting a higher starting current on, or similar. On systems with aux heat, I assume there are probably at least two breakers? One for the heat pump, one for the aux heat/air handler? Which breaker is tripping and what size is it?

[Tony Hwang]

Don't solely depend on wire colors. Have to understand the nomenclature of terminal markings. Some thermostats are not compatible with heap pump. Please start with reading the manual and from the typical wiring diagram there try to match your system.

[Tony Hwang]

And you have to go into service mode to set the options like you have one stage heat pump. Also you can test the system there. All in the manual. Also Honeywell support is very good if need help from them.

[trader_4]

Unless you buy one of their better there better thermostats, eg VisionPro. Then they tell you that they won't answer questions about how to change the system settings and you have to call one of those guys with saggy pants and a butt crack for $150.

[Tony Hwang]

RTH8500D is Vision Pro 8000 series. I never had problem with Honeywell tech support. Always prompt and gives correct answer to my questions. BTW, with that thermostat, if you run one more wire battery is only back up for power failure which means battery lasts LONG time. All in the manual. I have two Vision Pro 8000 series, one out at our 4 season cabin, one at downtown rental condo with split A/C and hot water heating system. At home I have wireless one with Redlink for Internet connection so I can control the system remotely from any where in the world as well as in/outdoor video surveillance cameras using DDNS.

[Robert T.]

Thank you all for your responses. I'm tempted to think that the wiring is fine and that it may be a breaker issue. The breaker that trips from time to time is the aux heat / electric furnace. Now, I have to find what's causing it to trip. Since I wrote the first note, it tripped twice at different intervals and times (one while asleep and once during the day) but I can't connect the dots yet.

[trader_4]

Baloney. It's not branded, marketed or sold as VisionPro. The "Pro" means something, ie that it's not meant to be sold retail, to consumers. The RTH8500D looks like a VP and has some of the features, but it's sold in retail channels. So, Honeywell will answer homeowner install questions on the RTH, but not on VP series.

Depends on what you consider a problem. If you buy an actual VisionPro thermostat and call up to ask how to change the setup settings, they will tell you to call an HVAC company and will refuse to answer your questions. Been there, done that.

[trader_4]

That is just resistance electric heat, right? So, there is no way mis-wiring a thermostat could cause that to happen. Might just be a bad breaker or there could be a fault in the heater.

[Ron in NY]

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About 15 years ago when my mother was still alive, she would call me a few times a week to tell me that the central A/C in her condo was out. I would go over there, and sure enough, the 30 amp breaker was tripped. I would reset it and a few days later it would trip again. I went nuts looking for a cause, and then I said "Screw it", and replaced the breaker. Never had a problem after that. I guess the breaker fatigued over the years and was tripping at a much lower current than it was supposed to. REPLACE THAT BREAKER !!! ======================================================== Remove the ZZZ from my E-mail address to send me E-mail.

[Tony Hwang]

8000 series has many varieties. Even basic one is quite robust in features. And it comes with a manual, quite thick booklet in English and Spanish. Or you can download it in PDF form which will need a small binder to keep it in order. Of course if you ask dumb question you'll get dumb answer or just stare in the eye or totally ignored. If you ask good intelligent question you get more than you asked for usually. Honeywell makes good stuffs in Mexico, vs. cheap ones are from China. I worked for Honeywell all my life after coming home from years overseas work with DOD. More than 40 years.

My store which is in a LEAD building has Vision Pro 8000 under Lennox badge. Their manual hid some important thing like how to go into service mode. Most manuals trouble-shooting section always says call service tech. Our Genie screw drive DC motor GDO manual does the same but I can work on any problem. I had to find out a fuse on a control board which was hidden in the schematics in the manual. Some people may have problem setting up the Intellicode remote or synchronizing new car remote to GDO. Now I am working on ways to take over new car PTS remote starter. Looks like firmware needs tweaks.

>

[Tony Hwang]

OP, did you set what kind of system you have in the service mode like heat pump or force air furnace, single stage or multi stage, and few other stuffs. If you have heat strip and old thermostat worked fine I don't think it is breaker issue. Go thru set up procedure and see if you missed any thing. You can also test the system basic operation in service mode.

[trader_4]

Of course non of that has any relevance to the fact that Honeywell will not provide phone support, answer questions for homeowners about how to install the VisionPro series. Words have meaning and "Pro" means that product series is not intended to be sold through retail channels to consumers. It's intended to be sold through pro HVAC channels and they are the ones that are supposed to install it. I've been there, done that. I called up Honeywell on a VisionPro thermostat question (Not the RTH8500, which isn't a VP), and they would not answer my install setup question. They told me to call one of those guys with loose pants and a butt crack showing.

Which also has no relevance to what I posted.