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Post by brubacca on Jan 12, 2019 0:00:37 GMT -5
While going to bed tonight (2 hours ago) I noticed that our fancy Honeywell Prestige thermostat was blanm (no power).
After a couple of hours of troubleshooting I figured out that we only have 11.97 VAC on the R and C terminals on the controller. That is the incoming wires to the controller and I verified this by removing them from the terminal block and measuring them.
Anyone know what to check next? And where? I guess our heat pump has a 120V to 24VAC transformer in it somewhere.
Am I on the right track?
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Post by ngmitter on Jan 12, 2019 8:52:47 GMT -5
HVAC engineer here. You are in the right track. I strictly do commercial, but a lot carries over into residential. I did some research and some residential thermostats are designed for 12V, but most are 24V. Depending on manufacturer, some of the 24V thermostats will work fine on a 12V power source.
As for the transformer, yes there is a 120V or 208V to 24V transformer typically on the control board of the heat pump.
If you jump the two wires to the thermostat together, what happens?
Also, please report back on the model number of the heat pump, thermostat, and transformer of you can access it.
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Post by brubacca on Jan 12, 2019 11:07:49 GMT -5
Thanks for chiming in. I typically work in the industrial sector also, I have been on the sales side of automation for more than a couple years. So I can use a meter and follow the wiring a bit. The physical location of things is not so apparent,
When the wires for R and C are terminated on the Honeywell Thermostat Control Board I get less than a volt, I had to remove them from their termination point to get a voltage measurement (the 12VAC). I definitely had what should have been 24VAC to the board. The control board calls for 24VAC (I'm used to DC in Automation).
I have a Honeywell Prestige IAQ 2.0 Thermostat and their wired control board (not wireless). It controls a Luxaire Heat Pump and for emergency heat we have an oil backup. The part number on the manual is a TH16B3621S. There is a control board in the outside part of the heat pump that I am going to try and access now. It has a diagnostic LED and a code display to read.
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Post by brubacca on Jan 12, 2019 12:39:38 GMT -5
I checked the HVAC board on the outside unit. It has power and a flashing green light. I think it means its in standby. I did see a small transformer on the circuit board labelled 1A, 24VAC, but as I said its on the board. Its not something that I can change. I have my HVAC guy coming this afternoon although I am not sure what he is going to be able to do.
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Post by autiger on Jan 13, 2019 12:32:58 GMT -5
I'm no HVAC guy. But a month ago I had a HW thermostat-no power and finally found I had a blown fuse 3A in the air-handler. Anyway best of luck on the repair
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Post by modicen on Jan 13, 2019 20:35:36 GMT -5
Does the tstat have batteries and have you checked them? Also like autiger said, check the little purple 3a fuse on the circuit board in the air handler, sometimes they can pop.
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Post by brubacca on Jan 13, 2019 22:30:09 GMT -5
We are back up with our emergency backup. It looks like we may have taken a high voltage spike which possibly damaged out units VFD. Can't run on Heat Pump, but can run the oil.
Just a refresher, on single phase in the home you get 220V right? Possibly 208v?
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