greenheck makeup air

[jeepfrk9]

hello,
What I've got is a greenheck makeup air unit TSU 218h40db 890,000 btu, honeywell burner control (blue box) and a maxitrol mr212d gas valve,a1044 amplifier, selectrastat temp control. whew...
the unit is only a few years old, customer has been reporting it blows cold air at times,(also shop guys said they've had to turn it off and on for it to fire, not sure if I belive them)everytime I show up it runs fine. I'm not really fimiluar with these...I'm gonna get a reo-stat tomarrow to go through the testing procedures but I think there gonna test good because it works when I'm there. Anyone know of and common problems with these that could cause these problems that I should look at?

Also how does the selectrastat control it, I think it controls the discharge air..sience it's in a large shop and it has alot of open doors I told them to leave it up at 90????
any help is sure apprecated!

[cold in alberta]

what part of country you live in?what part of day normally tripped?frost in your area?off on flame failure?need much more info

[jeepfrk9]

I live in the northwest...yes it's cold but it's been colder.....I dont know if it's a flame failure because it's running when I get there. I dont beleave this thing stores errors...

[tim fox]

see post in pro forum.

[lafayettetech]

any thing over 500,000 btu has to lock out on flame failure on the first try with no recycle. i worked on a few dravo direct fired mua units that have been modernized with maxitrol controls, i had the same thing, just cleaned the whole pilot assembly, made sure the minipeeper could see flame, and checked pressure to pilot. i did find a spider web on a minipeeper, it would send signals most of the time. anyways found out the guys in the factory would shut power off then on, reseting the control and it would run for a week, then that one time flame is not sensed on start up, it would lock out. then they would reset it. i hope this helps

[lafayettetech]

i havent got to work on any greenheck mua, but i imagine its direct fired from your description, their should be a sensor in the discharge air from the stat that modulates the main gas valve to keep a constant 72 degrees at the stat if thats what the stat is set on, their should be a diff on the back of the stat from 0 to like 30. all the ones i worked on had the diff set to 0 and their was no problems. i set them to 70 degrees in a factory and it keeps them happy

[matt8085]

I've worked on these and usually get the same call that the air feels cold. I get up to the roof and it's running fine. The problem is when it's 10 degrees outside, how much of a temp. rise do you expect to get. The supply air is still gonna feel cold.

[gasnowman]

The little blue box is the brain box. It could be a 7800 series control. If so, the history on systems ignition controls status are recorded in the memory of the control. I found that RE Michels sells the interface/burner control module the cheapest. You can not perform surgery without it.... May i also suggest an IOM .... good luck

[jeepfrk9]

looked at it again today and found it blowing what they called cold air, the honeywell flame controler showed no alarm, main, pilot, and flame led's were all lit...i figure what is happening is when they complain it's blowing cold air it's dropped to low fire?
what would make this drop to low fire...40 deg outside 55 in space, selectrastat set to 90.
It came back to high fire right in front of me. Found no other problems.....but I did disconnect the selectrastat form the maxatrol amp and the gv only throttled to 1/2 fire...I figured it would have went to low or off. S suspect a amp problem??? or discharge air sensor problem....any thoughts

[cold in alberta]

your best bet would to remove the remote selector from downstairs and wire it to the amplifier at the unit to save yourself some walking-then you can play with it at the unit and see if your gas valve is actually modulating -how is your dc volt signal to the gv-steady,fluctuating dramatically-when you pull the discharge air sensor wires off the amplifier does it go to high fire?if you pull the d.a.sensor off and it goes to high fire odds are it is not the amplifier.sounds like probably d.a.sensor pooped

[jeepfrk9]

thanks for the reply,
the gas valve seems to be modulating just fine..6 to 26 volts dc...fairly steady. I have not removed the da sensor wires from the amp...I will try that tomarrow.
Have you seen a da sensor work and than poop out for a while and then just start working again?

[Moose]

Have you cleaned the da sensor & tube? Should be mounted on the blower/duct - in the airflow. I have seen them full of dust/lint etc. Slows the response time.

[danscott]

Was it setup properly? The maxitol should be setup for the desired temp rise at winter design temp. If your design temp is 0 and you want to maintain 60 degree supply air, it needs to be setup for a 60 degree temp rise. I have a couple pds on the maxitrol controls. Its for a selectra A200, and I also have a greenheck Model DG manual in pdf form. Also is it firing at High fire or low fire. I had one that was trying to fire on high and modulate down, it was too much gas and wouldn't fire.(EMS control) I reversed it to fire on low and modulate up to maintain temp, and I haven't had a single problem with it since. (fingers crossed)