Hey folks, new guy here but looking for some assistance. I'm a general contractor and having some issues with a natural gas Trane package unit at the shop. Model # 4YCC3030A1075AA, Serial # 9193H8G9H. It's used in a storage area to just keep things above freezing during the winter and occasionally cool and remove some excess humidity during the summer. The furnace did fire up this fall and seemed to heat, though maybe a little cooler than normal but I can't say for sure. However, the other day I noticed it wasn't heating (people are not in that area regularly so not sure how long it had been malfunctioning) and started to diagnose the problem. I thought I'd give it a whirl at fixing before calling the HVAC guy.

When calling for heat, the combustion fan motor will turn on but I never hear the gas valve "click," no igniter, or anything similar to indicate it even tries to light. The CFM LED does flicker when it is running, though I don't know if that is normal or not. Per the diagnostic LED, it is showing a "Pressure Switch Problem." After doing some searching online, I tried a few things people suggested, but it appears to me that this unit has significantly different characteristics since it is a package unit. Some people talked about a clear tube from the pressure switch that can become clogged or even blown into to, I guess, simulate high pressure. There is no tube anywhere near this switch as far as I can tell. Does not appear to be any blockages on the combustion fan from what I could see. One of the things I did try was disconnecting and then jumping across the pressure switch terminals but it still threw the same code.

Does anyone have suggestions on where to go from here?

Thanks!
bjepple

 

Welcome to the forums.

I can't find the full service package for that unit. Based on the pictures of the pressure switch.... there is a connecting hose in your unit. I don't see any nipple on the draft inducer to connect to the pressure switch.

To test the pressure switch circuit........ disconnect the two leads from the pressure switch. Start a call for heat and then short the two wires. They cannot be shorted before the draft inducer starts running. The igniter won't glow until the pressure switch proves vacuum.

Some what helpful manual but not complete (pdf)