Older Rheem rooftop Package

[Cliff Naylor]

I cant identify this Rheem unit installed about 1988 - 90. Here is the outline drawing.
https://picasaweb.google.com/lh/photo/9LSBPjgkBTeNrF9_Ki1tKUKweslNWMH7r3Ysd8TeCs4?feat=d irectlink


Also others here.

https://picasaweb.google.com/113403583336321407877/LosBanosFurnace?authuser=0&authkey=Gv1sRgCJPXjaSJuqoj&feat=directlink

Problem is fan motor is on low all the time. If I call for heat, fan goes to high and blows out warm air. Wiring Diagram in in bad shape. states that it is a Honeywell. Drawing # 90-22141-01
Need all the help you guys can give.

Thanks

[Markus Keller]

Rheem unit Ok. The board is what would be a Honeywell. The board typically has 3-4 connection taps. low, medium and high. Some units have a tap to 'park' a lead. Fan motor speed for heat or AC is dictated by which lead is on which tap. AC = high. Heat is typically low or medium.
Sorry don't remember which color is which.
I also don't understand how the motor is always on low and goes to high when turned on. Sounds like a conflicting statement. When is the motor on low?
Could be a bad board but doesn't seem likely.

[Cliff Naylor]

The motor is on low at all times. If i remove the thermostat, the blower motor is still on low. According to what I have read, blower should be low on heat and high on cool. It appears that motor relay is activated all the time. I'm looking for a readable diagram. So heating works but fan is on high. When it reached its set-point, blower motor goes to low speed and stays there.

[Jack Feldmann]

If you have a 1988 Rheem gas pak unit, you have a very good chance of having a cracked heat exchanger. I'll go out on a limb here and try to predict where it might be.....

The left side of the far right burn chamber, about 6" inside. Vertical crack about 3" long. There may be more.

[Garry Sorrells]

If you have removed the thermostat (disconnected), I would look for a short. Either in thermostat wire or in the unit it self. Have you run test at board in unit for live line to fan?

[Steven Saville]

As far as the fan running on low speed continuously, I would suspect the fan/limit control. If it is a Honeywell control, it may be stuck, or due to age, not rotating to the point of opening the fan circuit. It may be that the fan "off" setting just needs to be set slightly higher. After removing the fan/limit control cover, while calling for heat, watch the fan/limit control. As the temperature rises in the heat exchanger, the control should rotate to 1.) turn on the blower, 2.) turn off the burner if the high limit setting is reached. With heat off, the control should rotate and turn off the blower once the "fan" off setting is reached.

Without more information, not sure why the fan goes to "high" though.

FYI - Fan speed motor leads are generally:
Black = High (cooling)
Blue = Medium (not generally used)
Red = Low (heating)
White = Neutral

[Cliff Naylor]

I think were on to something here. I'll be checking the fan limit control. It could be bad and stuck on. Thanks for the guidance. Ill see what i find today.

[Jack Feldmann]

While you are at it, pull off the cover to the burn chambers and take a look inside. A cracked heat exchanger is not something you want to ignore.
Just saying.........

[Cliff Naylor]

Bingo...Problem. Honeywell fan controller is bad. It's a 5" model with a broken Bi Metal twister goodie (don't know the technical name). I have ordered one. Thanks for the Help. As far as a crack in the heat exchanger, I spent about an hour inspecting it also using a carbon monoxide sniffer. We didn't find anything at all. Unit looks like it had been only slightly used before i got it. House is located in California central valley where winter rarely gets below 60 Deg. and summer are in the 90's to 110's daily. Thanks to everyone for all the help.