Heater troubleshooting on 123
 

My heat doesnt come really warm till about 10min. after car up to temp, I think its monovalve but not 100%. Any ideas??

240 or 300 series?

300td sorry

Is this a chevy or ford 300td and what year?

Peter

I also suspect it is the monovalve. I was getting no heat. Changed the monovalve and that fixed it. It is an easy job on the 123. Just do a search and you will find instructions with pictures. Part cost about $25.00. Also check you auxillary water pump. Just follow the heater hose until you see a small electric pump. You can jumper wire it to the battery and make sure it spins. Good luck.

Any more info on Electric Water Pump?

jumper it and it spins, then what? How is it controlled?
When should the connector have power?
Why do I need it?

Trying to fix an intermittent heat issue. 83 300TD. Not Ford or Chebby. ;)

SHELLNEKOV, Please put year and type of car in your profile then you wont get Ford, Chevy? answers. The mono valve was used from 1981 thru 85 in the 123 chassis, thats why the year of your car is important. The aux water pump works at idle and low RPM to force the coolant up hill to the heater core. Electrically failed, cool air at idle. Not needed once the water pump is spinning fast enough. Simply remove the 4 screws holding the cover on the mono valve (ENGINE OFF AND COOL) reach in and lift up the internal shaft and rubber diaphram. Note how the stacking of the washers go so it goes back together properly. Pull out around the diaphrams circumference and look for a tear in the rubber. Torn, needs a mono valve repair kit. Assembly filled with rust? needs a new mono valve.

What was I doing on September 23, 2004?

Hmm well I was a freshmen in high school. Actually during that week I think I decided to switch from violin to viola! That was one of the best decisions I ever did. I made districts and regionals in those funny PMEA festivals as well as 2nd chair in the local jr. Philhamonic. I still play in my college's orchestra :)


Oh and this years old thread: check the aspirator hose by pulling the glove compartment. Mine rotted apart and stopped working. I replaced it with a large vacuum hose and my intermittent heat started working again.

monovalve question
 

I have a 87 300SDL with similar heater problems. Does the information on this thread also apply to the 126? thanks, Bob

There is a simple test for the monovalve. Just remove power and you should have more heat than you can stand.


I did a lot of testing on my car recently with a meter. On the 85 I have found that the aux. water pump only runs when the defrost button is pushed or if you have the ACC wheel in the max. position (in the detent). In any other position the aux. water pump is off.

There is a temp sensor that cuts out the heater (fan?) until the engine is up to temperature unless the controls are in the defrost position. I would suspect that sensor. I think it is the one at the thermostat but I am not sure. If everything works fine after that 10 minutes I doubt it is the monovalve or the auxilliary pump.

what are mean outdoor temperatures?

my heat sux, but it really sux when its below zero. I wear pac boots for long drives- real comfortable to drive in.
I also cover 80% of radiator w/ cardboard during cold months.

There is nothing like getting an answer to a question 5-6 years after it gets posted. Hey, I guess better late than never! ;). Wonder if he even still has the car. Sorry, had to. Kerry, that would be my first place to look too...For what it is worth.