Goodman air handler A36-20,, not hot enuff

[mattn124]

Hey,, new to the forum,, look like it will be a good investment at $5 !  I need some help/advice with my furnace.

I have an electric Goodman indoor air handler in my basement. It was here when I bought this house in Dec of 1999.  I am not sure how old it is.  Model number A36-20.

It has both heating elements in it as well as my ac coils for the air conditioning.  It sits upright and the air flows upward through it, always passing thru the a-coil before passing over the heating elements.

Lately it just has not been getting hot enough.  I am not an hvac repair-man,, but I have a  degree in automation and am familiar with how to use a meter and not scared to work on electronics.. 

 The wire going from one circuit breaker on the power supply to the 1st (top) heating element actually melted and broke apart the other day,, causing the breaker to trip.

When the furnace first kicks on you can hear clicks of the saftey overload switches shutting off power to 2 elements after it runs for a  minute or so.

It seems like an airflow problem.. as if there is not enough air moving through the unit and the heating elements get too hot so they get shut off...  The filter is new,, I also clean the entire thing out twice a year,, including the a-coil..  Just a month ago I cleaned out the a-coil with a steamer, and shop-vac/bruch once dry. You can shine a flashlight through the a-coil anywhere.

If I have the front cover off of the unit and let it run, everything is fine.  The air coming out of the register vents upstairs is good and warm and lots of airflow. Of course,, I cant run it like this since the air is not filtered with the motor exposed to the open air...   As soon as I close the thing up and turn it on,, you can hear the overloads click and the air gets cool out of the vents with a noticable drop in pressure as well.

  All four elements have the same voltage drop across them as well as the same amp reading on them,,  or course I cant check this with the cover on, so I can't tell which one(s) are being shut off.. but I'd bet it's the top 2, they are furthest away from the fan.

Over the past couple years I have dealt with this problem, except for the burnt wire..  Over this time I have replaced the timed-delayed relay that all of the heating elements connect to with a factory replacement part, and all four of the limilt switches on the heating elements.

   I have a schematic of the circuits and I am positive they are installed correctly.  In fact,, I had called out a local hvac repair company,, they inspected it when I told them that, they agreed it was properly installed,,

    At that time,, they said I needed a fan relay and I paid for them to install one.. it did not fix the problem either.

So,, if I have the cover off and it can move all the air it wants, it operates as it should.  When I re-assemble the unit and make it use the cold air returns for it's air supply, it shuts 1 or 2 heating elements off.

To my eyes,, the heating elements look ok when I take them out and look at them.

Any suggestions?  Do I need new elements? Is maybe the fan motor old and weak and not moving enough air?  Are there any other tests I can perform? Anybody know where I can find out what the voltage/amp readings should be at different parts of the unit while running?

I had been given advice that maybe 4 elements was too much heat for my house(main floor about 950 sq ft) and that I should unplug one of them. Is that sound advice? 

   Also,, if I do this,, would it not send too much power to the remaining heating elements?  Some of them are on the same leg of the relay as others, and I thought that might cause too large of a voltage drop on one of the elements damaging it or worse..

I know this is a long message.. Thank you very much to anyone who reads all of it,, and thank you even more to anyone who takes the time to reply.

Thanks

Matt

[hvacdrd]

[user=18893]mattn124[/user] wrote:

If I have the front cover off of the unit and let it run, everything is fine.  The air coming out of the register vents upstairs is good and warm and lots of airflow. Of course,, I cant run it like this since the air is not filtered with the motor exposed to the open air...   As soon as I close the thing up and turn it on,, you can hear the overloads click and the air gets cool out of the vents with a noticable drop in pressure as well.

Air flow is king...

a couple items of interest. A36-20 is a 3 ton a-coil with 20KW electric heat. Acutally it is equipped with one 14.8KW heater and one 4.8KW according to the part breakdown. Giving you 19.6KW x 3413BTU/KW = 66894 BTU - yep a bit much for the sq. ft. However most electric heat systems stage on the elements using a sequencer to prevent all elements from coming on at once. Disconnecting an element or two is an option but this does not solve the airflow problem which will show up again when it comes to running the a/c.

The limit is rated at 150F to open and closes at 105F so I would expect normal discharge temps to be 110-125 if airflow was correct.

Back to the air flow, start with the basics by making sure the blower is running the correct direction. The blades should cup the air. If you install the door when the blower is running is it difficult to remove? Is it a strong vaccum? If so you will need to look at the return air setup. A-coil is clean, filter is clean, only leaves restricted or undersized ductwork.

I can't dig up any service literature on this model for the specs you requested but I think we can get you in the ballpark. See what information you can get from the nameplate, maybe even post a wiring diagram.

[That Guy]

You need to find all of the return air vents and make sure they are not blocked or restricted. Once you have all of them cleaned up, check your airflow. If its still not enough, then your return air duct work is too small. It may have been undersized from the start. Depending on your local building codes you may be able to run another return air vent into another room to get the extra air you need.

[mattn124]

Thanks for the replies. 

Here's a wiring diagram, hvacdrd. It's just a picture taken of a diagram sticker on the cover, but it turned out ok.

I had all my vents and returns cleaned recently by a local company.  It was just the vents themselves and a few feet into the ductwork.  I know the main trunks of the ductwork are very dirty.  While that guy was here he cut an access panel to look, very dirty inside.  

I didn't think that would effect airflow all that much though,,  I guess it can? I mean,, there's a 1/4" to 1/2" maybe at most on hair/dust/funk inside the duct work.  My return ductwork is 14" x 8"  on return vent the furthest away from the unit, and that expands to 24"x 8" about 1/2way to the furnace, as well as is that larger size from the 2nd air return, which is very close to the furnace itself.

   There does seem to be a restriction right by the furnace.  The return ductwork runs along the ceiling in the basement and drops straight down behind the furnace to feed it return air. At about 1/2way down this point, the ductwork looks newer, as if installed at the time of the furnace,, all the other dutwork seems to be original with the house(built in 1960)  Anyway,, it drops to 20"x 8" before it makes the last corner into the furnace.

So,, sounds like you both may be onto something with the idea that the ductwork is too small.   Before I hack anything up though, I wouldn't mind trying other solutions that are cheaper/easier,,,  as long as the air blowing out of the vents is warmer than the wind chill it creates I'll be happy! haha

Thanks again for the replies! 

matt

[mattn124]

Ok, I I tried to put an attachment on that last post,,,   I cant seem to get anything to post.  Are you not allowed to add attachments until you have a higher reputation level or something? 

I will try and figure it out and post the wiring diagram when I can.

matt

[mattn124]

the file size was too large.

[mattn124]

here some more info

[hvacdrd]

The easiest way to determine if it is the return air ductwork would be to disconnect a portion of it where it drops down to the furnace. If airflow improves you know where to look. If not we keep thinking.

When you state you can see through the A-coil do you mean you can get a look from the bottom side? Given the amount of dirt in the ductwork it would be logical that the A-coil was plugged on the bottom side long before you moved in...get a good look at the inlet side if possible.

[mattn124]

I'll see what I can do as far as removing the ductwork,,,  might be difficult because of where/how it is installed,, but I might be replacing it anyway..

I can tell you that yes, when the cover is off and the furnace is running and I place the cover back on it, it is hard to remove,, there's a good vacuum there. 

Also,, yes, I was able to get to both sides of the a-coil when I cleaned it.  The way it's positioned in the furnace allows me to take another piece off and I'm looking at the side of it,, you know,, the side that makes the triangle shape, so I'm able to get underneath it. 

      I cant really SEE through it...  What I use as kind of a test to see if it's clean, is that I stick my arm inside(the inlet side) up underneath it with a flashlight on.  If I can see the light from the flashlignt on the inside walls of the furnace,, then I know light is passing through the a-coil...   I know it's probably not an industry standard test,, but I fifgured if light will pass through then air should as well..

It may be a few days to a week before I can buy or fabricate some new ductwork..  Could I unplug one of the heating elements just for the time being?  If so,,, how do I know which one?  My concern is that some of them turn on at different times, and maybe some of them turn on at the same time,,,  I dont want to overload one of more of the elements and burn it up,, or worse.

Thanks again for your help

Matt

[AYUDANTE]

i know you said you cleaned your unit, but what about your blower wheel? what kind of condition is it in?  are your registers balanced correctly? or maybe you have a collapse return to your air handler. 

the rpms should be approx 1075. and the amp draw on your red wire from your fan motor approx 2.6  Some where on the tag u can find the running load apms for the fan motor (RLA).  your temp relay will control the box temp, and cycle as per settings.

So check for any problems with the return duct since you stated that the unit is the basement, maybe some thing is in there or collapsed.

Ayudante