york limit problems

[litjoe]

I have been having aproblem with 2 york b3hp030a06a. blower running all the time. reset breaker and unit fine till it happens again may be months. the heat kit is a warren on both of these units. when high temp limit opens blower goes to high speed and does not cycle till breaker is reset. talked to york about this was told unit should have had source 1 heat kit instead of warren. i checked and had a 40 rise with nothing but aux heat on. blower motor is x 13 and is set on highest speed. anyone else had problems with this. Duct size is 16 inch on return and supply. evap coil clean, no duct problems. I know I can not have a 40 rise with out limit problems. thanks

[DOGBOY]

I have experienced the same thingonly it just happens once a winter. york told me if it only does it occasionally to have homeowner reset breaker. I am thinking it is from dirty air filter causing low airflow and the high limit is opening. as the only time we get the call is when it is very very cold outside.

dogboy

[litjoe]

thanks

[garyed]

You didn't say how many kw heat strips you had running or what the amp draw was on them. Unless you've got about 15 kw on a 2.5 ton system it sounds like you have low airflow. Add a dirty filter & the HP running too & the high limit tripping makes sense. I would do a temp rise method to see what the actual cfm's are.

[litjoe]

10 kw heat. amp draw 41.6. with filter out

[garyed]

10 kw heat. amp draw 41.6. with filter out

OK then lets assume you've got 240v:
CFM = btus/TDx1.08
41.6 * 240v * 9984 * 3.413 = 34075 /40 * 1.08 = 789 cfm's on a 2.5 ton system. If you've got anything lower than 240v that gives you even less CFM's. Sounds like you've got a low airflow problem causing high TD.
Maybe you've got a dirty coil too.

[sammyray]

Could be the supply air grills are close in some rooms.

[litjoe]

you are right it is a airfow problem. york tech i talked to said they were having a lot of calls on these units.where they used warren heat kit instead of york. says warren to sensitive on limit. but with 40 td. it is just to much coils clean return clean. did not check all the supplies. i will do that when it when i go back out. thanks.

[SuperDave89]

I'd also check the blower wheel when the air scoops start to get gummed up with dirt they dont push enough air.

[DOGBOY]

OK then lets assume you've got 240v:
CFM = btus/TDx1.08
41.6 * 240v * 9984 * 3.413 = 34075 /40 * 1.08 = 789 cfm's on a 2.5 ton system. If you've got anything lower than 240v that gives you even less CFM's. Sounds like you've got a low airflow problem causing high TD.
Maybe you've got a dirty coil too.

but assuming 244v he is only 65 cfm away from the 1000 needed. and if voltage is higher he is even closer.

oh yea mine to were warren heater strips

dogboy

[garyed]

but assuming 244v he is only 65 cfm away from the 1000 needed. and if voltage is higher he is even closer.

oh yea mine to were warren heater strips

dogboy

I only get about 13 cfm's more at 244 v. which is still pretty low for a heat pump. Add another approx. 30 degrees for the heat pump & you're looking at around 70 TD when aux. heat is running. That's enough to trip a high limit.
I did make a mistake the way I wrote the equation though:

41.6 * 240v * 9984 * 3.413 = 34075 /40 * 1.08 = 789 cfm's

should have been:

41.6 * 240v = 9984 * 3.413 = 34075 /40 * 1.08 = 789 cfm's

[DOGBOY]

Where I am at we put outdoor t-stats on the heat strips and don't allow them to come on untill it drops below 40* and with the pro 8000's we keep the strips off again untill below 40* so when our heat strips are on we are not getting a 30* rise across the indoor coil but a more realistic 15* - 20*. And I know the op's company or area may not do it this way but it helps with power bills when people set back heatpumps in the winter.

and with your math I can not for the life of me to come up with your answer. what am I doing wrong?

41.6 * 240 = 9984 * 3.413 = 34075 / 40 = 852 * 1.08 = 920

dogboy

[garyed]

Where I am at we put outdoor t-stats on the heat strips and don't allow them to come on untill it drops below 40* and with the pro 8000's we keep the strips off again untill below 40* so when our heat strips are on we are not getting a 30* rise across the indoor coil but a more realistic 15* - 20*. And I know the op's company or area may not do it this way but it helps with power bills when people set back heatpumps in the winter.

and with your math I can not for the life of me to come up with your answer. what am I doing wrong?

41.6 * 240 = 9984 * 3.413 = 34075 / 40 = 852 * 1.08 = 920

dogboy

Again I wrote the equation out improperly. The 1.08 should have been in brackets with the TD because you multiply the two first & use that figure to divide with. I took that part for granted which is a no no in mathematics.

CFM= BTU's/(TD*1.08)

So its really :
41.6 * 240 = 9984 * 3.413 = 34075 / (40* 1.08) = 789