Chrysler Repair: Low Heater output, dodge grand caravan, cable sheath

Question
The heater output is low on my 1994 dodge grand caravan 3.3L engine with 136,000 miles. The coolant level is good.  I have already replaced the thermostat, backflushed the heater core and replaced the contol valve.  There was good flow through the heater core when  I flushed it. I put a new water pump on last summer.  What else do I look for?  Could the new thermostat be faulty and stuck open?  It still seems to take a long time for the engine to come up to temp.  There is also a vacumn leak under the dash which makes the blower switch to the defrost under moderate to hard acceleration.  Could that impact it?  Thanks for you help!

Answer
P.S. If it if like the car heater units, Mark, you may have a loose, broken or disconnected cable between the heat contol slider (that regulates the temp between hot and cold on the control panel) and the door that directs the incoming air across the heater core or the a/c evaporater core. So while you are looking for the vacuum leak and have the control panel ajar to look inside, check the slider motion and observe whether its cable seems to be loose between the slider lever and the door lever on the top of the heater unit. The end of the cable sheath is held in place by a removable clip type disconnect (push on the tab on the side that faces you and lift out) and then there is a clip on the cable itself right at the door lever. To adjust it, you set the control knob slider at full cold, then allow the end of the cable to slide in its clip and rotate the door lever full counter clockwise. Then observe that you have full range of door lever motion. I trust this car type heater setup is the same as in your van.
Roland




Hi Mark,
The slow to rise temp gauge is suspicious of perhaps you have a too low temp thermostat or a faulty thermostat. Did you use one that opens at 195? which is what the shop manuals usually call for. Even so, you might want to check it out on the stove top in a pot of water with an accurate thermometer to see at what temp it really begins to open.
The vacuum leak under the dash is something you might do well to correct because it certainly controls the air distribution doors, and maybe it has something to do with the door that controls the air flow over the heater core. I don't have a manual or knowledge of the heater system for the vans, but I would want to correct that vacuum hose leak to be sure that is not the cause of your low heat output.
It is a line that runs from the power brake canister thru the fire wall and to the heater control panel where the vacuum is switched around to various door actuators via the push botton controls. So if you took off the bezel that surrounds the console you could then get the control panel released from its mounting and isolate the leaky vacuum line. You might also be able to check the line at the firewall on the cabin side and trace it all the way to the control panel. Listening would be the best way to find it, perhaps using a rubber tube in your ear like a stethiscope to help focus the hearing better.
There is a heater by-pass valve in the engine compartment that is put into play when you go to the recirc max A/C mode, but my understanding is that the by-passing of the heater requires the vacuum to actuate that valve, rather than the other way around, so unless it is set up differently in the vans it would seem that a vacuum leak might prevent the by-passing of the heater rather than causing a by-pass of the heater. But why not feel how warm the hose to the radiator are, they should be both hot if the system isn't set to bypass the heater. If one is cold then I would suspect that the by-pass valve is open and that is why you aren't getting much heat.
Let me know what you find out.
Roland