Multi zones HVAC system not pumping heat to first floor

[H Hui]

I have a multi zones (3 zones) HVAC at home for my 3 different floors, and the HVAC unit is located at the deck level (4th floor).

Recently I notice my ground floor cannot keep the heat and even though the thermostat is set to a higher temperature, but the temperature keeps very low, and there isn't much warm air coming out from the vent. And my 4th floor, where the hvac unit is located, has been extremely warm. I can hear the heater is running but the warm air just can't reach the first floor, it feels like the warm air is trapped on the 4th floor for some reason.

I've looked at the pipes connected to each floor next to the hvac unit, and the one that goes to first floor is labeled as "by-pass".

I've tried to replace the air filter, and even remove it, and it works for a while but it is now kinda stop pumping air down again.

Can someone give me some clue or suggest a way to find out what's wrong?

Thanks.

 

[JerryR]

Sounds like zone dampers are not functioning as they should.

There should be a zone control board that opens and controls at least 3 zone dampers.

What zone board do you have?

A knowledgable HVAC tech should easily troubleshoot the system.

 

[Sponsor]

 

[H Hui]

Sorry for a late reply as I was out of town. Below are more pictures of my furnace and control board.

 

[H Hui]

I might be wrong about the by-pass is going to first floor also, as I just realize there is another pipe behind the by-pass other than the 3rd floor and 2nd floor ones.

 

[DougB]

Those are motorized dampers. If the motor fails, or the damper gets 'hung up' it won't open the duct.

Turn all the thermostats to 60 degrees. You stand by the damper in question. Then have someone turn the 'bad' zone thermostat to the max. See if you can hear / see the damper operate. If you have a DVM - see if there is power to the motor, etc.

 

[JerryR]

That's a Honeywell 3 zone control board. They are very reliable.

It's hard to see but it looks like each zone is a 2-wire damper rather than a 3-wire damper. A 3-wire damper is motor driven both open and closed.

2-wire dampers are usually wired spring OPEN power CLOSED. Look at the zone board where the two wires go. If the zone damper wires are connected to M1 and M6 they are spring OPEN power CLOSED. If wired M1 and M4 they are wired power OPEN.

It looks like they may be wired M1-M6 spring OPEN power CLOSED. If so A broken spring in the actuator will cause the damper to remain closed all the time and never get heat to that zone. If that's the case its a simple fix to replace the RDMH actuator on the failed damper. If the damper plate is hung up then the damper needs to be replaced.

 

[JerryR]

Yep. RDMH actuators are SPRING loaded. Replacements run about $75.

Here's a typical replacement actuator if that's what has failed.
http://www.newegg.com/Product/Product.aspx?Item=119-0009-00003