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Phil
Phil, Mechanical Engineer
Category: HVAC
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Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I'm trying to convert my McQuay thermostat (circa 1985) to a

Customer Question

Hey there! I'm trying to convert my McQuay thermostat (circa 1985) to a Nest thermostat, I think it's line voltage
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: Just trying to upgrade, really. Though I'm not convinced that the motor that adjusts the valve for the radiator flow is working properly
JA: Do you plan on doing the work yourself?
Customer: yes, I've done a few thermostat conversions but haven't gotten my toes wet with converting line voltage to the low voltage type. I'm pretty experienced with electronics, though
JA: Anything else we should know to help you best?
Customer: I think that's all I really have at the moment ok, can you tell me a little more about how this service works??
Submitted: 25 days ago.
Category: HVAC
Expert:  airheatman replied 25 days ago.

What is model on the McQuay and what does it control?

Customer: replied 25 days ago.
Model HSB-HKD-030C.It has 3 switches. One for on/off, one for high/low (both control the fan) and one knob for temperature. From what it looks like the temperature knob triggers a solenoid that opens/closes the pipe to the radiator looking part. When it's turned to 'hot' the solenoid opens the valve and water (i assume) flows to the radiator fins and generates the heat.What I want to do is connect a low voltage thermostat that controls everything. I think I can probably use relays from the low voltage thermostat to control the high voltage gates; what I'm unclear on is what type of relays to use and where exactly all of those would be connected to a low voltage thermostat. In other words, which leads from a standard low voltage thermostat would control on/off of fan, and which would control the solenoid.. unless I'm missing something (which is entirely possible)
Expert:  airheatman replied 25 days ago.

I have opened to other experts.The Nest is designed for 24v systems. To convert everything over to a 24v system is gong to require quiet a bit of time figuring out what relays you need to control what.

I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk and delay getting assistance..Please stand by to see if another expert can assist further

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