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s6skuzy01 03-08-2009 10:17 AM

Carrier Furnace Error Code 33
Have a 11 yr old Carrier 80% furnace 58RAV. Back in the fall of 2008 the furnace would go on and shutoff. Called an HVAC mechanic and they replaced a the limit switch and it worked fine for about a month. Then, every 30-45 days since the repair, we get an error code 33. I replaced the filter (it wasnt more than 30-45 days old). Problem went away for 3-045 days then happened again. Called HVAC mechanic out and he just adjusted the fan speed up a notch and replaced the filter. 45 days later it happened again. As soon as I replace the filter the error code stops. The filters are dirty, but we have gone longer than 30-45 days before the initial repair without getting the error. We will call teh HVAC mechanic again and see what the scoop is, but the last time out they didnt seem to know what was causing the error. Any ideas?


yuri 03-08-2009 11:42 AM

Lack of air flow causing the limit switch to trip. That is a reverse flow furnace I believe. If it is sitting on top of a A/C coil then that coil may be dirty and slowing down the airflow. Make sure you do not use one of those very tight 3M filters as they slow down the air too much. Make sure ALL your vents are open and clean. A MERV 7 or 8 filter from HDepot is good enough and change it MONTHLY or pay more for gas/stress the furnace.

s6skuzy01 03-08-2009 11:57 AM

Thanks, we went to the cheaper filters after the first call out to the HVAC mechanic. We're gonna him him another call tomorrow and see, but it seems like once the filter is changed the problem goes away till the next time it gets dirty. Seems the filter fixes the issue but not for long. Could the ac coil still cause that?

All vents are open and unblocked also...

yuri 03-08-2009 12:57 PM

YES. Just like a blocked radiator causes your car to overheat.

s6skuzy01 03-08-2009 02:01 PM

Just checked the AC coil and there was very little dust on it...

yuri 03-08-2009 03:22 PM

Get your tech to check the temp rise thru the unit and see if it is within the specs on the rating plate. He can also do a meter clock test with the gas meter to make sure it is not overfired or check the manifold pressure with a manometer. If this is all foreign to him then you need a more experienced tech.

Good Luck

s6skuzy01 03-09-2009 10:19 AM

Tech is here
Did a temp rise test and found:

Without filter - 130
With old filter - 155 and temp sensor tripped

He adjusted the gas and the temp range was withing specs. When they replaced the limit switch, they put one in that allowed for a larger temp range, so they didnt think that was the issue. Also said to use a different filter. Our current filter is a MERV 6.

We'll see if this fixes it...

beenthere 03-09-2009 10:36 AM

The temp rise is 155, or the discharge air temp is 155.

If the rise(difference between return air temp, and discharge air temp) is 130 or 155, something is still majorly wrong.

You want the proper rated limit switch.
And teh problem corrected, not covered up with an unsafe band aid.

s6skuzy01 03-09-2009 11:34 AM

Sorry, the discharge temp was 155...

beenthere 03-09-2009 11:42 AM

If the return temp was 70, that still gives you an 85 rise.
Too much for many furnaces.
Your furnace will have am allowable temp rise rating inside the burner panel.
Look at it, and see what its limits are.

If 85 is above its limit. Then its not fixed right.
And will have a shortened life span.

PS: An A/C coil can look clean on the surface, but be dirty in between the fins, and restrict air flow.

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