Heater Blows Cold Air

[Waldo]

This is my first post..But I'll try to be clear.

My 82 300 CD Turbo has been cooling just fine all summer here in Arizona.

However, now winter is here , yes even here in AZ. I set the heater for hot

air & it works just fine for about a half hr, goes to 120 Deg. I turn the

roller down a bit & the air goes full cold. I have reset the roller to hot a

couple of times & the warm air returns, but goes cold again.

The question of course is...Where's the fault? Control, Monovalve,?

Sensor,?

I've been following this forum for some time & I'm sure there are a good

number of you guys ,& Gals, who know this as just "Old stuff". This is

driving me nuts.. HELP!

[Mölyapina]

Originally Posted by Waldo

goes to 120 Deg

The temp in the interior, right? I ask because 120°C is the overheat point for the engine on the gauge .

[whunter]

Originally Posted by Waldo

This is my first post..But I'll try to be clear.

My 82 300 CD Turbo has been cooling just fine all summer here in Arizona.

However, now winter is here , yes even here in AZ. I set the heater for hot

air & it works just fine for about a half hr, goes to 120 Deg. I turn the

roller down a bit & the air goes full cold. I have reset the roller to hot a

couple of times & the warm air returns, but goes cold again.

The question of course is...Where's the fault? Control, Monovalve,?

Sensor,?

I've been following this forum for some time & I'm sure there are a good

number of you guys ,& Gals, who know this as just "Old stuff". This is

driving me nuts.. HELP!

Check the coolant level with the engine running.

Replace the damaged Mono valve.

.

[Waldo]

The 120 F is on a thermometer in the vent. Air temp coming into the cab.

Coolant is ok.

Thanks for the comeback & opinions. I'll check the Mono too. I had one

replaced about a year ago,...could be damaged. I disconnected the aux

pump when I read they could take out your control.