Carrier Weather maker 9200

Shellyjames1942

I have a query regarding a heating system in a prayer hall, and I'm seeking some guidance. The setup includes two identical Carrier Weathermaker 9200 gas-fired furnaces with separate pilots. Both furnaces contribute hot air to a common header duct, and the entire system is controlled by a single thermostat.

My question pertains to how these furnaces switch over or operate simultaneously. I'm curious about the mechanism that drives the switching relay to transition between the two furnaces. Currently, we observe that only one furnace is running most of the time, and there's limited switching.

Given the age of these systems, I'm wondering if anyone has insights into the operational logic of the switching mechanism or suggestions on why the switching might not be happening frequently.

Your expertise and advice would be immensely valuable. I appreciate any detailed explanations or troubleshooting tips you can provide. I am an old school late from 40's .
Thank you ,
James

HVACNUT

They might be "Twinned". Check the circuit boards to see if they have the terminals shown in green.

EdTheHeaterMan

I thought this looked familiar:

I just answered this on a PM

This is what I said:

If I recall correctly, the Carrier Weathermaker with a 9200 designation was a furnace that used a hot surface ignitor to light the burners each time there’s a call for heat. So, your statement about a separate pilot is somewhat confusing. That particular furnace series has at least three different models that I recall. The 58MVP was a variable input furnace and the 58MCA and 58MXA were fixed input furnaces. I believe that all three models used a secondary heat exchanger to reduce the exhaust temperature below the condensing point and therefore have some sort of water from the exhaust that will drain out of the furnace during operation. Also, that lower exhaust temperature allows the venting system to be made of PVC plastic piping.

Many of the furnaces models in that range had a maximum input of 150,000 BTUh making them a great choice for most homes, however, older equipment in some larger homes had capacities of 200,000 to 300,000 BTU input. In order to use these new smaller units in those older buildings, a twinning kit was developed by many manufacturers, like Carrier, to allow the use of two smaller furnaces to do the job of one larger furnace. This is no doubt what has happened here.

In order to further assist you in how this system should operate and how it does operate, I would need the actual model number of each furnace. The model numbers of all Carrier furnaces start with the number 58 then usually 2 or 3 letters like MCA the several more numbers to designate the size of the burner like 090 or 140. After that are some letters and number combinations that indicate the size of the blower fan and cabinet with and other things. If you can provide me with the model number of both furnaces, I may be able to answer your query.

tim smith

Are you sure its wired for either or both operation. A lot of the systems like this were set up to run together to meet the demand of the building as there usually is not a single residential furnace that had the output to meet sanctuary's etc. We would set them up with back draft dampers if it was an either or system. If one was off and other on they would recirculate warm air from the running one backwards from the one off and back into return of one running, Not good. So both furnaces would have backdraft damper. Carrier also made a twinning kit with If I remember right, dpst relay and limits for blower compartments so if one blower failed and started to recirculate it would shut them both off. This was for the all on twinning systems. Did them for churches, memorial halls etc. Was decent cost effective solution when pulling a large old low boy furnace that may have been 400000 btu and 3 or 4000 cfm.

Shellyjames1942

Thank you all . I will do some research and get back to you ! God Bless you all !

EBEBRATT-Ed

If they discharge into the same plenum they are probably twinned together, and they should run at the same time.

If they run separately how do you keep discharge air from going backward through the other furnace unless you have motorized dampers.