herman nelson unit ventilator

[iowa tech]

I have a school with old Herman Nelson Unit ventilators. This stuff is from 1967 and is all pnuematics. Does anyone have any literature on this stuff? i'm new to pnuematics.motor low speed not working. no info on units
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[Dallas Duster]

Does this unit have the push button speed selector switch with the transformer mounted on top of it ?

[flange]

the p newmatics are pretty simplistic in those old things, get a pneumatic book and do some reading, or as my first boss would recommend....find a bad version of each part on the job, order a new one, and keep the paperwork in a binder until you know how it works. as far as the motors, they were a tad special if i recall, and your local motor shop has seen them enough to know what one will get you close as far as rpms and frame size etc. ours can get you exact replacements if you know what model unit ventilator you have.

[iowa tech]

Does this unit have the push button speed selector switch with the transformer mounted on top of it ?

yes
hi
low
off

[Dallas Duster]

yes
hi
low
off

You need to see about locating the transformer wiring diagram you either have a 1/8 hp or a 1/4 hp motor. Transformer sends a different voltage over to the motor. I would only go OEM on this bad boy it's the only way to go that I know of. You could have a bad transformer or a bad switch. Conpare readings with a similar unit if you can.

[DeltaT]

I have a school with old Herman Nelson Unit ventilators. This stuff is from 1967 and is all pnuematics. Does anyone have any literature on this stuff? i'm new to pnuematics.motor low speed not working. no info on units
Edit/Delete Message

If the motor operates in high speed correctly then the problem either lies in the motors low speed windings, and if so you need a new motor; on in the control relay that powers the low speed winding.

Simply test the low speed tap to see if it's receiving its 115 volt, typically. And if it is then the motor needs replacing. If there is no voltage present on the low speed motor tap then trace the wiring back to the relay that switched the motor from high speed to low speed and replace the relay if it is not providing voltage to the low speed motor tap.

Whatever you do, DO NOT send power to both motor speed taps at the same time.

[Dallas Duster]

yes
hi
low
off

You need to see about locating the transformer wiring diagram you either have a 1/8 hp or a 1/4 hp motor. Transformer sends a different voltage over to the motor. I would only go OEM on this bad boy it's the only way to go that I know of. You could have a bad transformer or a bad switch. Conpare readings with a similar unit if you can.

[iowa tech]

so with no numbers how can i get wiring diagram

do all units have relays ?

back of switch has 7 spots for wires don't know what is what

[DeltaT]

so with no numbers how can i get wiring diagram

do all units have relays ?

back of switch has 7 spots for wires don't know what is what

Are you comfortable with tracing out wires? And can you use a multimeter to read voltages to the different taps/relays/fan speed switches?

[iowa tech]

i can do that

would like to have wiring diagram to work from to make it easyer

[The Doctor]

If you call H-H in Des Moines, they can get the parts for those units. Last year had a real similar situation in CAM schools out in your neck of the woods(old pneumatics with issues of their own coupled with a failed fan switching center) It makes for an interesting troubleshooting session.

Still do not have drawings to forward to you though.

[iowa tech]

do you know how the switch is wired?

[The Doctor]

No...been looking for the pocket notebook with those notes in it for the part numbers or just for the notes from the chat with H-H.

It seems that the switches had two speeds and that H-H asks what colors are the switching buttons.

In our case, I had to jump from the power terminal to a speed terminal because the guts of the switch weren't working. And I had to have a pneumatics guru confirm that a day/night stat was ALSO part of the problem on the same machine.
If I find the notebook/part numbers I'll bump the thread.

[statman]

I am pretty sure I can help you . In the unit ventilators, you will most likely find a heating valve, a damper motor(s) a P/E or E/P, (p is pneumatic, e is electric),a low limit and as well as a mixed air control along with some relays, etc. each is identifiable with numbers. I am fairly certain I can provide cut sheets to you and we can probably figure out how that unit works- based on what you find inside. At my website, you can get cut sheets on the more modern pneumatics, but give me a call after you have done a little legwork.
STATMAN www.eprinc.net

[Control Man]

Many also had adjustable pneumatic relay for night setback operation ( ran on low speed ) over the years found many ADJUSTED and low speed would no longer work.

What model are you working on , have most of their MANUALS from late 50's to late 60's.

[targetman]

I don't have anything else to add, but just wanted to say that I have worked on those units also.

[iowa tech]

model asp3125-347

also check plug with no motor had 120 to net on one leg

check other leg high speed 65v low 75v does that help

i think i have a bad motor right

[Sexton]

I am having a similar problem. Do you happen to have a readable electrical schematic?

[Dallas Duster]

I am having a similar problem. Do you happen to have a readable electrical schematic?

For the motor speed transformer? I just might.

[Sexton]

For the motor speed transformer? I just might.

I have a number of these units in the church and every wiring diagram is faded to the point that they can't be read. I would appreciate any info/diagrams you have. Thanks. NS

[spike1974]

Many also had adjustable pneumatic relay for night setback operation ( ran on low speed ) over the years found many ADJUSTED and low speed would no longer work.

What model are you working on , have most of their MANUALS from late 50's to late 60's.

model # MWADFVG6041-60

I'm working on some of these also, cannot find much at all on these.