Combustion analysis ok .
Filter removed still hot .
Difference in temp is very close to limit..??
Any ideas
Did you measure the temperature rise? Or try increasing the fan speed? It could be an airflow problem. Maybe the air conditioning coil is dirty. Maybe the furnace is oversized or the duct work is undersized.
Quote from: Admin on January 25, 2019, 07:02:30 PM
Did you measure the temperature rise? Or try increasing the fan speed? It could be an airflow problem. Maybe the air conditioning coil is dirty. Maybe the furnace is oversized or the duct work is undersized.
Yes temp rise .
That part i dont understand is its been working fine for 5 years .
A coil was replaced last year I didn't check it but I assumed would be ok..
Gas valve pressure is 3.5
So why would I have to adjust fan speed etc ?
And how about static pressure ? I've seen some systems work fine at 1+.....
If air filter, duct work static pressure, A coil, gas pressure all check out, you sometimes need to up the fan speed a bit to get the temp rise in the right spot. It may have been running hot for 5 years... And 3.5 sounds a hair over for what I usually see as the recommended gas pressure on high. I'd put it at 3.4, but I doubt that tiny difference is the problem.
Static pressure is 1.0 and has been working ok for 5 years.
I've seen on systems at 1.3 working fine .
This is what has me confused.
Is this a high efficiency furnace? If so I would wash the blower wheel if it's dirty and check the underside of the secondary heat exchanger and make sure it's not plugged with dirt.
If they replaced the AC last year the new coil is likely bigger than the old one. Maybe air could escape around the old coil but the new one is wider and forces all the air through the coil.
1" w.c. seems a little high. What's the pressure drop above and below the A coil?
Has the customer moved furniture lately, maybe blocking a return in the process?
1" TESP isn't great, in fact that's terrible, just because another furnace ran ok at 1.3" doesn't mean they all will.
I would do what Admin suggested and clean the blower wheel, did you look at the secondary heat exchanger?
Is the customer using a different filter than they normally do?
The main reason furnaces don't shut off on limit is because the fan keeps em cool. Definitely an air flow issue. That's why when u have to check the limit you have to stop the fan!
Quote from: wantboost on January 25, 2019, 07:22:51 PM
Quote from: Admin on January 25, 2019, 07:02:30 PM
Did you measure the temperature rise? Or try increasing the fan speed? It could be an airflow problem. Maybe the air conditioning coil is dirty. Maybe the furnace is oversized or the duct work is undersized.
Yes temp rise .
That part i dont understand is its been working fine for 5 years .
A coil was replaced last year I didn't check it but I assumed would be ok..
Gas valve pressure is 3.5
So why would I have to adjust fan speed etc ?
And how about static pressure ? I've seen some systems work fine at 1+.....
1. Systems running TESP of 1+ are not working fine. They might seem to be working, but are not working fine.
2. You would have to adjust to move more air across the heat exchanger. More air to remove more heat from the exchanger.
3. Check fan speed, blower wheel, and secondary heat exchanger for dust and lint. Check for closed off supplies, blocked returns, dirty/restrictive filter, and an undersized return drop.
4. Do a temp rise after all that. If the temp rise is good and the furnace trips limit, replace the limit.