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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8385
Experience:  Furnace, A/C and heat pump specialist.
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I have several BARD HVAC in run away heat, even though I 't

Customer Question

I have several BARD HVAC in run away heat, even though I don't call for heat from the stat. The Unit calls briefly for heat when the temp drops blow 55 degrees, then stops calling according to the stat a couple of minutes later, but the room heats from 55 degrees to 85 degrees over the course of several hours.
I believe the issue lies in the fact that the unit has the O/B jumpered to the W1. The current stat I have does not dis engage the O/B relay after the heat call. Since it is just the changeover, it stays on. However, this seems to cause an issue when the weather is real cold on certain units. I can provide graph images.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Our first step is to determine if the compressor keeps running or the heating elements are what keeps running.If the elements are what keeps going, the issue id most likely a sticking sequencer.

If you have a volt meter we can troubleshoot to find out exactly what is going on.

Looking at the diagram that jumper is supposed to stay in place to make sure reversing valve is energized anytime W1 gets power.

Now if the reversing valve is staying in heat mode when you go to cool, we would want to troubleshoot the reversing valve and see if we are making and breaking voltage at the solenoid.

Either way, even if reversing valve stayed in heat mode, when thermostat is satisfied Y should lose 24v and cut compressor off so that would not cause the issue you are having about it still blowing hot air.

We can go from here.