overriding Goodman "Comfortbridge" communicating mode

[RustyShackleford]

So I've just finished installing a Goodman GSZC7 two-stage heat pump. It works pretty well, but it could be working better. What I failed to comprehend before I decided on this model was that the system was designed to be controlled by a dead simple thermostat: from the installation manual:

For all cooling calls the system only requires a single Y input from the thermostat. For all heating calls (including applications with backup electric heater kits) the system only requires a single W input from the thermostat. Internal algorithms will control all available cooling and heating stages based on these inputs.

Sounds good on paper, but it seems like it could be better. For example, when the thermostat suddenly calls for much cooler temperatures when peak electricity hours end at 6pm, it first runs the compressor low-stage for a selectable duration (30 minutes max) and if the thermostat isn't satisfied (which it won't be in this situation) it kicks into high-stage. When selecting high-stage, it runs the air handler at 1500cfm, which seems awfully high for a 3-ton system, and it sounds like there's a tornado in the crawlspace.

I may be mistaken, but I feel like a good multi-stage thermostat (such as https://www.honeywellhome.com/us/en...-wifi-programmable-thermostat-th8321wf1001-u/ ) could be smarter than this; for example, it would realize that the set-point temperature is 5 degrees lower than the current indoor temperature, and select high-stage immediately. But I'm completely unclear as to whether I'm able to run the system in this fashion. The installation manuals have sections for "communicating" systems (from which the above citation is taken) and for "non-communicating systems". The non-communicating sections show typical wiring for a two-stage system with a two-stage thermostat. What I can't figure out is whether this is intended for pairing either of the components with a non-communicating type partner, or whether it's acceptable to wire these two communicating units in this fashion.

I suppose I could just try it; I seriously doubt it could actually cause damage, but I'd have to spring $100+ for the thermostat. I've tried at the hvac-talk forum, but those people are a-holes, absolutely no help. Though hvacdirect.com was great with the purchase, their tech support seems very poor (they say they can't answer phone, leave a message, and I haven't heard back after 2-3 days).

It any clever person feels like doing me a solid, here are the installation docs. The relevant discussion is at pages 10-11 of the first and pages 16-17 of the second.

 

[Pinesmoke]

I'll look in the morning, enjoying a bourbon right now 😁

Gonna sound flip and I don't mean it that way, have you talked to Goodman tech? There should be a setting to control how it deals with the Thermo

 

[RustyShackleford]

I'll look in the morning, enjoying a bourbon right now 😁

Thanks, and cheers !

Gonna sound flip and I don't mean it that way, have you talked to Goodman tech? There should be a setting to control how it deals with the Thermo

I can't figure out how to get Goodman to talk to me. They seem to want everything done thru the installer. My installer is a moonlighting cryogenic tech. He's smart and knows his freon and such, but has no experience with this kind of communicating system and is not licensed (so not registered with Goodman).

You do setup stuff with a phone app that talks to the units via Bluetooth. But it doesn't have any such setting - just has various delays and trims. I think it figures it out by how you have things wired. I didn't do anything to tell it that it was a communicating system, but just hooked the thermostat to the air hander as on a normal one-stage (without auxiliary heat) system, and then ran two conductors between the '1' and '2' terminals on the air handler and compressor as per this figure

 

[EatenByLimestone]

It seems like a lot of these companies are like this. I had this problem from Buderus (Bosch). I solved it by calling in as Rusty from Rusty’s Heating and Cooling.

If you were called in to fix the system, you’re not a certified installer. You’re just Chuck in a truck with some tools. Client called in to see if you could fix the tornado sound in the crawl space. You read the manual and saw it says this. Can you solve this issue by doing xxxxc or should I do it a different way?

 

[Pinesmoke]

Rusty
Working on first coffee and I'll look more closely on a bit (after more coffee)

It appears wire 1/2 are the coms between the units. When you look in the legacy wiring in the HP setup they aren't connected. Then you go to a standard 2 stage wiring for the thermo. So with a good 2 stage hp thermo should be straight forward.

Does the app allow you to set fan speeds based on various factors. Normally heat runs a different speed than cool. Each stage will run differently.

A good stat will give you a circulation mode as well. Runs for example 30min/hour at 50%fan speed. In a non com setup I would think it would run at stage 1 speed since all it can do is call for fan.

Take this rusty with low caffeine in mind. I'll look again.

Back to coffee 😂

ETA I had a Goodman system in a condo from 10 years back and the fan was horrendous at higher speeds.

 

[Pinesmoke]

I was looking a bit more. There are some dip switches to be set for a non com thermo. Doesn't seem too rough.

I looked some at thermos and a thought came through the morning fog.

With the HP and AH having logic boards to tie the system together with the stat it is entirely possible to loose some functionality with using a non com / non Goodman stat .

I'll use my trane system as an example, which is FINALLY running right but that's a different story.

I set a humidity set point and based on how far over set point/ temp set point/ and over shoot temp settings the system will go into "dehumidifier mode" slowing the fan to pull more water onto the coils. This has various levels of aggressiveness based purely in the firmware of the 3 logic board involved. If I had a non trane stat this functionality would not be there.

The Goodman stats are pricier than the Honeywell but there may be a deal from HVAC direct since you got the system from them.

It would open up the system to its full capacity.

Still drinking........ coffee

 

[Pinesmoke]

Original deleted

 

[RustyShackleford]

Many thanks !

It appears wire 1/2 are the coms between the units. When you look in the legacy wiring in the HP setup they aren't connected. Then you go to a standard 2 stage wiring for the thermo. So with a good 2 stage hp thermo should be straight forward.

Yes, wires 1/2 are how I have it connected now.

Does the app allow you to set fan speeds based on various factors. Normally heat runs a different speed than cool. Each stage will run differently.

Just noticed on p. 27 of air handler manual, using 3 push-buttons to set various airflow stuff (including for communicating mode, so possibly I could fix the excesssive fan speed thing without re-wiring). Also on p. 18 can select system type.

ETA I had a Goodman system in a condo from 10 years back and the fan was horrendous at higher speeds.

Well, I don't blame Goodman, just the cfm, but seems odd it'd ever run 1500cfm for a 3-ton system.

I was looking a bit more. There are some dip switches to be set for a non com thermo. Doesn't seem too rough.

The ones for defrost time (on p. 7 of compressor manual) ? I don't see any others.

With the HP and AH having logic boards to tie the system together with the stat it is entirely possible to loose some functionality with using a non com / non Goodman stat .

Well that Honeywell I linked does seem to have a humidity sensor and outputs for calling for dehumidification.

 

[Pinesmoke]

Many thanks !

Yes, wires 1/2 are how I have it connected now.

The legacy wiring diagram I seem to remember those get disconnected.

Just noticed on p. 27 of air handler manual, using 3 push-buttons to set various airflow stuff (including for communicating mode, so possibly I could fix the excesssive fan speed thing without re-wiring). Also on p. 18 can select system type.

Well, I don't blame Goodman, just the cfm, but seems odd it'd ever run 1500cfm for a 3-ton system.

The ones for defrost time (on p. 7 of compressor manual) ? I don't see any others.

Yes the defrost. In full com mode probably it's probably handled but com is disconnected for normal stat.

Well that Honeywell I linked does seem to have a humidity sensor and outputs for calling for dehumidification.

If I remember from this morning that are contacts to control a whole house dehumidifier. I was talking about the main HP system running in a way it doesn't cool so fast and pulls more humidity out.

 

[RustyShackleford]

Guy at stackexchange suggested tying Y and Y2 wires from air handler to current thermostat's Y output, to see how that works - in order to get an indication if this "legacy" re-wiring is likely to work, without first purchasing a new thermostat. Is that how two-stage compressors work, IOW would it be ok with having both Y inputs asserted simultaneously ?

 

[Pinesmoke]

Sounds like the old stat is single stage it would always run in second that way but should work.

Look at the legacy schematic. The stat signals carry through both systems. The stat is controlling EACH system through wires, not the com wiring , 1/2.

I thought, without deep dive this morning you can run the comfort bridge, ie coms with a coms stat OR legacy stat with different wiring

 

[RustyShackleford]

Sounds like the old stat is single stage it would always run in second that way but should work.

It has a W output, but single-stage except for that. So do I understand correctly that two-stage compressors (in general) want to see Y asserted for 1st-stage and BOTH asserted for high-stage (as opposed to only Y2) ? So if I wire Y and Y2 to my single-stage thermostat's Y output, I'll always be running high-stage ? Which should give me a clue if this "legacy" plan will work.

Look at the legacy schematic. The stat signals carry through both systems. The stat is controlling EACH system through wires, not the com wiring , 1/2.

Got it, thanks.

 

[Pinesmoke]

Y y2 are separate they are your 2 stages of cool. W is your heat.

 

[RustyShackleford]

I finally got in touch with a tech support guy at hvacdirect.com (left a message with the guy who sold me the unit and he did an "expedite") and he said yeah, they've had a number of people do what I'm considering. Gave me his direct email in case I need add'l help. I'm pleased to hear this and pleased with them.

 

[EatenByLimestone]

Excellent outcome!

 

[Pinesmoke]

Tieing y1 y2 together should lock you into 2 stage. Getting set up to stage of the stat will let it cruise on first stage when it can or use it to bump the temp to hold it there based on how tight you have the stat set to hold.

This weeks data off of mine. 3/2 ton hp

 

[RustyShackleford]

Cool graphs. Not such which 'stat you have. I hope this Honeywell one I'm considering (link in OP) can do that.

 

[RustyShackleford]

@Pinesmoke Thanks for your help. I still can't find the DIP switches you mentioned in post #6 (other than the ones on p. 7 of the compressor document for defrost timing).

 

[Pinesmoke]

@Pinesmoke Thanks for your help. I still can't find the DIP switches you mentioned in post #6 (other than the ones on p. 7 of the compressor document for defrost timing).

Those are the only ones I saw in the docs Rusty.

 

[Pinesmoke]

Cool graphs. Not such which 'stat you have. I hope this Honeywell one I'm considering (link in OP) can do that.

It's a Trane stat so it's pretty tightly tied to the other hardware. It's possible it could have some history functions written in. Honeywell is good stuff .

 

[RustyShackleford]

Another thing I noticed, the thermostat connection on the air handler has a terminal marked DH/Y2. The air-handler manual says the DH input "allows the air handler’s circulator blower to operate at a reduced speed during a combined thermostat call for cooling and a dehumidification". Which is great. Except, if this connection is used for dehumidification, how do I select first- and second-stage of the heat pump ? Do I have to sacrifice one or the other ? And if so, how do I tell the system which way I'm using the connection ? The attached image (from the manual) shows the recommended "legacy" wiring. Maybe you can't have a dehumdification input unless you're wiring as a "communicating" system ?

 

[Pinesmoke]

Another thing I noticed, the thermostat connection on the air handler has a terminal marked DH/Y2. The air-handler manual says the DH input "allows the air handler’s circulator blower to operate at a reduced speed during a combined thermostat call for cooling and a dehumidification". Which is great. Except, if this connection is used for dehumidification, how do I select first- and second-stage of the heat pump ? Do I have to sacrifice one or the other ? And if so, how do I tell the system which way I'm using the connection ? The attached image (from the manual) shows the recommended "legacy" wiring. Maybe you can't have a dehumdification input unless you're wiring as a "communicating" system ?

View attachment 328452

Rusty that would be a question for HVACdirect tech guy. Speaking theoretically it could be from the stat, y first stage, y2 second, both is DH. I don't have a positive answer on this one. That input is into the airhandler so it must be a combonation of inputs to trigger DH mode.