Carrier RTU trouble light

[timtanguay]

I've noticed that a number of carrier units that i've done planned maintenance on have had the trouble code 1 "fan delay modified" or some such message. A couple of guys I work with said not to worry about it.

Out of curiosity, does this trouble light have something to do with an after market Low ambient Control mechanism? I live in vancouver, where the shoulder seasons often require fan cycling on the condensers to maintain head.

Any explanations as to why the light is going off would be great. I hate not knowing why a unit is doing something.


Thanks!!
Tim

[james mo]

It means that the high temp limit tripped in heat and the control adjusted the fan delay off time

[timtanguay]

It means that the high temp limit tripped in heat and the control adjusted the fan delay off time

Perfect. Thanks.

Also, just noticed it is the evap fan not condenser. :P

Any common causes for the temp limit to trip out on carrier units?

[2sac]

Check the same things you'd normally check

[rundawg]

I've noticed that a number of carrier units that i've done planned maintenance on have had the trouble code 1 "fan delay modified" or some such message. A couple of guys I work with said not to worry about it.

This Fan ON/OFF delay modified means :

High limit switch opens during heat exchanger warm-up period before fan-on delay expires.

or

Limit switch opens within three minutes after blower-off delay timing in Heating mode.


Some Carrier units like the 48GS or 48GX, have a FIXED 45 second on and off delay, so there has been NO modification of the delay time.


The bottom line is you have most likely have poor airflow - dirty filter, dirty evap coil, duct work issues ect........

I would do a static pressure test to help pinpoint the problem.

I would not just disregard it like your buddies at work suggested.

[timtanguay]

This Fan ON/OFF delay modified means :

The bottom line is you have most likely have poor airflow - dirty filter, dirty evap coil, duct work issues ect........

I would do a static pressure test to help pinpoint the problem.

I would not just disregard it like your buddies at work suggested.

Oh okay, thanks for the information. The filters themselves and the coil were all pretty clean. The filters in question get a change quarterly. They were still mostly clean, and the indoor coil looked close to spotless. They had recently had a brush down and a good hose down with some of that lemony fresh no spray coil cleaner.

So you reckon it is poor air flow causing the issue then. I'm new to the trade. Can you measure this from the rooftop? I imagine you'd use a differential manometer. Where would you put the probes? Obviously one facing the blower, where would the second one go?

As for required CFM, should I use the values from the manufacturer literature or do some calculations.

Cheers,
Tim

[rundawg]

The filters themselves and the coil were all pretty clean. The filters in question get a change quarterly. They were still mostly clean, and the indoor coil looked close to spotless

I also would not rule out a weak blower motor. Did you check the capacitor on the motor to see if it was good?

Did you clean the blower wheel? Those can get really dirty and reduce your airflow.

Can you measure this from the rooftop? I imagine you'd use a differential manometer. Where would you put the probes? Obviously one facing the blower, where would the second one go?

You would need to test in the supply and return ducts as close to the unit as possible.

You would have to read the notes on the blower performance chart to see if the filter was included in the units static pressure readings.

It doesn't matter if the static probe is pointing into, or away from, the airflow.

You can use a 0-1"wc Dwyer magnehelic or a manometer like the Testo 510.

As for required CFM, should I use the values from the manufacturer literature or do some calculations.

Either should work.