Carrier 40aq air handler electric heat
No heat call, found the filter was plugged solid and coil.
With the blower door off Im bypassing the coil and the unit works.
I would assume that with the door on and the unit calling for heat 2 things would happen because of lack of air.
1- Air switch would not prove and heat strips would not energize.
2- Heat strips would energize and limit switch would open ( limit switch didnt not open when tested)
Its in a dark ceiling thats very tight and hard to work in, theres no tech data on site as far as schematics. I was able to locate the limit switches but not the air switch if there is one.
Carrier says unit has been obsolete since 1989
I have a call into the carrier tech line to see if I can get my hands on some data.
Tomorrow Im going back to the job to clean the coil, just trying to get more information.
What are you saying? Explain more
the 40AQ does not have a proving switch. it has a sequencer that parallels the blower, it has a thermal limit.
It`s better to be silent and thought the fool; than speak and remove all doubt.
Your not being very clear. But, first I would make sure you have good air flow. Clean that coil and change the filter. Check to make sure the elements aren't damaged. Are any overloads/ limits tripped. Is there a sequencer that might be bad. Is the heat relay energized. Is the thermostat calling for heat. Visually track things down. You can check alot of things without a schematic if you take one wire at a time. Good luck
Thermal limits would just open and reset when cool. Sounds like you just need to get your airflow taken care of
because of the age and if the coil is that plugged up it will be hard to clean properly without taking it out. And because of the tight space you have to work in. I would look at the labor cost verses putting in a new coil or unit.