A/H not starting when Fan is set to Auto

rrabih

Hello,
I have an old Carrier programmable Thermostat*, a boiler (with separated Tank), and a Glowcore A/H.
when the Thermostat send in a signal for heat, the boiler kicks and starts, but not the A/H (Fan) when it is set to Fan Auto. When Fan is set to On it works.

The same A/H and thermostat is used for AC in the summer, and it works properly (The A/H starts when thermostat calls while Fan is set to Auto), this means that the issue is only when the call is for heat!

I wonder if it is an issue with the thermostat or with a relay somewhere (A/H) ...

For now to keep warm in this cold weather, we let the Fan set to ON all the time, not very efficient..

any help?

*The programmable thermostat is somehow old, is the one below
https://www.climatesystems.net/wp-content/uploads/2017/06/dimond-manual-carrier-programmable-thermostat.pdf


Thank you

SuperTech

Its not the thermostat causing the problem, I can assure you that the problem is something with the air handler.  Usually hydro air units use either an aquastat strapped to the hot water line supplying the coil or a time delay relay to energize the fans heating speed.  Newer hydro air units utilize a circuit board to control the fan. Cooling fan speed is controlled by a separate relay. This is also the same fan speed that is energized by switching the fan to on.
Since you still have heat I think it is more likely that your air handler controls the heating fan speed with a time delay relay rather than an aquastat. Is there any way you can take pictures of your air handler and the electrical components in it?

SuperTech

Didn't you post about this problem last winter? This is an awful long time to go without it being repaired.  

If it were my unit I would install a CB201V control board. This board is designed to control any hydro air unit with a PSC fan motor. 

rrabih

thank you for the quick response!
you are right, it is more likely using a time delay relay.. 
tried to take some photo as opening it is not an easy task, id photos are not clear will do the complete job tomorrow 

rrabih

yes, I had this issue but actually passed the winter and because this was working properly for Cooling it was forgotten:-(

SuperTech

I remember your previous post because I have never heard of Glowcore, but that is just a First Co. hydro air unit rebadged. I have seen these units wired up a lot of different ways, but I don't recognize what you have by your pictures.  

But it should be pretty simple. You should have three relays. One for the cooling fan speed, that looks like its probably the one on the bottom in the first picture. You also have a separate heating fan speed relay and a relay to the boiler. 

The Robertshaw and ICM controls are both time delay relays, perhaps a picture of the wiring diagram will reveal what which one does. 

SuperTech

After researching that model number it appears that the VDX units use the same fan speed for heat and cooling. That's a bit different from what I typically see. Is this air handler heated by a tank type hot water heater? One of those relays could be for a circulator pump. But I would really need to see the diagram and pictures of the system to determine whats what. 

Its possible that the heating controls were field installed....its late. I'll think about it more in the morning. 

rrabih

thank you, 
yes tank is separate from the boiler itself separate from A/H
I will take some photos tomorrow, just wonder if what you asking is inside the A/H or outside it?

HVACNUT

It looks like in the top photo, white from the thermostat goes to the TDR and energizes the coil on the heat relay above it, for the boiler circulator. 
The output side of the TDR energizes the coil on the fan relay below it.
Check if there's 24v at the fan relay coil.
If no, faulty TDR.
If yes, faulty fan relay. (Assuming it's the same fan speed as G on the thermostat).