Honeywell M9185D 1004

icesailor

Can anyone tell me how to troubleshoot a Honeywell M9185D Modutrol with a T991A Potentiometer controller?

It runs a Honeywell modulating water valve for a heat recovery unit in a nursing home. The valve stopped modulating. I can open it by jumping the 24 volt Red to Blue, it will open the valve. I got the manual off the Internet but it doesn't tell me how to troubleshoot/test it electrically. I understand how it works, just not how to test it.

Paul48

Assumtions

Check the motor stroke before connecting the linkage:

a. Remove R-W-B jumper.(with this jumper, motor is at mid-stroke)

b. Short R-W. The motor should drive fully clockwise

(viewed from power end).

c. Remove R-W jumper and short R-B. The motor

should drive fully counterclockwise (viewed from

power end).

If the motor functions OK as tested,I'd assume the problem was with the potentiometer. I'm approaching it, the same way as you though.

icesailor

Driving Home:

Paul,

This motor has no linkage but has an adapter on the horizontal end that connects to a cam that drives the motor open. It is spring loaded so that when power is removed to the motor, it will automatically close.

If I jump from the 24 volt power (Red) and the first terminal (I think is blue), the valve will power open. I can't remember if I remove the wires on the T991 Potentiometer/proportional control or not. There is a "Bridge Circuit" inside the motor and the red, blue and white go from the motor to the control. There is a carbon piece in the T991. When you set the T991, and the temperature and pointer are equal, you should have equal something across the carbon and the bridge loop in the motorized valve will be equal. If the temperature goes up or down, the current will switch one way or the other, opening or closing the valve and controlling the temperature in the air handler by throttling the cater going into the coil.

I have been futzing around with this thing for 20+ years. No one has ever told me a way to test the components. I changed the T991 but I don't think that it was the problem, it never has been that I have been sure of. But I don't know how to test the system. If the potentiometer inside the motor isn't receiving a signal from the T991, it would stay closed, which it does. If I put my multi-tester on the leads, I don't know what I am testing. I get no voltage but if I disconnect all the wires on the T991, I will get a Ohm reading in the "middle".

There is a circuit board inside the motor housing. Either the Close cam is dirty, or the board is fried. But it will power open if I jump it. The motor isn't cheap, and I hate to continue to play trial and error mechanic. I can justify the T991 because it is really covered with salt air corrosion. The motor is another story. And found  another motor in another part of the unit that is probably bad. I want a way to check it.

I hate the trial and error method.

Thanks for your response and thoughts. Keep them coming. 

SWEI

135 Ohm potentiometer control

uses a Wheatstone bridge to compare the unknown resistance (position of the valve) with a known resistance to provide position feedback.



http://www.hvacmechanic.com/viewtopic.php?f=11&t=631

http://www.buildingcontrolworkbench.com/Portals/1/GrayBook/Gelec90.htm

Paul48

icesailor

From the documents that SWEI provided, it confirms that is the way to test the motor. Depending on which terminals you jump, the motor should move to a corresponding position. It eliminates all other possiblities, and if it doesn't, the motor is bad.Don't pay any attention to how it is connected.You're only concerned that it moves to the end of the stroke one way, then the other, or to mid-stroke.

icesailor

Testing:

Paul,

I got a PDF from someone at HVAC-talk.com for that motorized valve. There was a flow type chart that said that if you connect red to both blue and white, and the motor opens half way, change the motor. That's what it now does.

Funny thing is that when I started, nothing did anything. The more I futzed with it, the more it started to work. I gave it a squirt with electrical contact cleaner and it then started to open half way.

I'll order a new motor tomorrow.

Thanks for the help.



http://96.61.63.50/techlib/Honeywell/Honeywell_ModutrolIVMotor_M94_iom_D1190_632195.pdf