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Old 12-20-2001, 05:09 PM
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Question cold air from defroster vent

first of all, it is south dakota cold. is it natural for cold air to come out of the defrost vent when warm air is coming out the bottom vent and under the seats? it seems that they are offsetting each other. the defrost vent is warm when it is only on, but cold when either in the economy mode and/or air compressor mode. i've read before on the forum it might be the monovalue, but not sure. thanks for any help and happy holidays
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Old 12-20-2001, 08:43 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Replace the monovalve then recheck.
Donnie Drummonds
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Old 12-21-2001, 12:45 PM
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where is the monovalue located on the motor and are there any special tools needed to repair it? i am buying the repair kit from fastlane, i assume that's the way to go
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Old 12-21-2001, 03:02 PM
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smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
The monovalve is inboard of the battery on the firewall under the diagnostic port.

- remove 2 philips screws behind the transmission dipstick
- move the diagnostic port out of the way
- remove 4 flathead screws on top of the monovalve
-- it might help to disconnect the 1/2" OD hose above the monovalve
--- go easy because the fitting is plastic
- lift the monovalve cartridge and top plate out of the housing
- note the order of washers as you remove the cartridge
- installation is reverse from this point

The amount of coolant I lost didn't even register in the reservoir. Maybe there's a pocket of air in my block now.

The monovalve usually fails through tearing of the rubber seal on the valve or the rubber diaphragm.

[added on 03 Jan] I've added a monovalve album to for some visuals to go with these descriptions for future reference on monovalve cartridge repair and/or replacement. Corrections are always appreciated.

91 300SE
81 300SD

Last edited by sixto; 01-03-2002 at 05:58 AM.
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Old 12-24-2001, 11:47 PM
Posts: n/a
new monovalue, same problem

unfortunately after i changed with monovalve with sixto's directions (thanks man), the cold air out of the defroster still exists. any other ideas, or maybe that's the way it is.
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