Joined: Sat Mar 25 2006, 07:31PM
Location: Nebo, NC
Posts: 86
The heater blower voltage supply is about 1.25 volts leass than battery voltage on the high "heater" setting in our '71 300. The output of the heater is, therefore, inadequate. I have not actually measured voltage on the "A/C" setting, but it seems to be adequate in that mode. Our '70 300's heater works great, so I know that this is not how they are supposed to operate. Moreover, the '71's blower works fine when I jump it to battery voltage.
I am not new to these cars, but I have never had one exhibit this symptom. It has been recommended that I check the switch, but just getting to the switch is a nightmare. Has anybody else ever had to deal with this problem?
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Certainly sounds like either the switch, dirty connections or possibly a bad ground. The blower circuit is fairly straight forward, power enters at the switch and depending upon the switch position feeds the blower motor through some wire wound resistors and finally exits the motor to ground. Run a jumper from the blower case to the battery negative post and see if that solves the problem. If it does then the motor isn't properly grounded. If it doesn't then put a meter on the power lead feeding the switch, if it's low then you may have a dirty bulkhead connection. If the switch is getting full voltage and the motor ground is good, then the only thing left is the switch.
Joined: Sat Mar 25 2006, 07:31PM
Location: Nebo, NC
Posts: 86
Fury 440,
Thanks for the post. Bulkhead connctor has been cleaned and dielectric-greased. Ground wire terminal has been cleaned and re-secured to windsield wiper motor lug where I found it. Haven't measured the voltage supplied to the switch or tried grounding the motor case directly to the battery terminal. I'll check those out.
I think I'd rather freeze than mess with that switch. As chilly as it has been, Ill probably end up breaking something as I work with all of the cold plastic that's in the way!
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
I guess one step before giving up is to get a spray can of contact cleaner and hose down the switch contacts while cycling the switch a bunch of times.
Do you have a circuit diagram? If not I can scan in one for a 70 Fury - which should be the same as yours.
Joined: Sat Mar 25 2006, 07:31PM
Location: Nebo, NC
Posts: 86
Thanks for the further input, guys. Here is what I have learned since my last post: first, though the blower motor definitely runs faster on the A/C setting, the voltage supplied by its wiring under the hood DOES NOT CHANGE regardless of wheter thje switch is set on "Heat" or "A/C"! Second, the voltage to the heat/A/C circuit at the fuse box appears to be lower than that of some of the other circuits (about 1 - 1.5 volts). Clearly, this information creates more questions than it does answers. And, for the record, grounding the blower case to the battery changes nothing.
Joined: Sat Dec 10 2005, 04:28PM
Location: United States
Posts: 4954
Since the blower is the heaviest load, let's look at a few other things.
71 Chrysler has the ignition in the column, unless it's tilt. Teh blower runs through the accessory circuit on the ignition switch. If the switch is usually not the problem. Check the connector at the bottom of the column. If it's an original connector, it will probably show burning in the connector. If it does, cut that wire out and use two insulated male/female to rejoin it. This is a typical place for low voltage.
Technically, you should be seeing 12.5 VDC at the fuse block. I suggest you get a voltmeter to be more accurate
My blower runs faster on A/C setting than heater. I think this is a normal operation. Could not find any mention of it in my 70 Chrysler service manual.. Maybe something explaining it is in a 69 book, seeing as that is first year for fuselage and new control head.
Joined: Sat Mar 25 2006, 07:31PM
Location: Nebo, NC
Posts: 86
[quote]Since the blower is the heaviest load, let's look at a few other things.
71 Chrysler has the ignition in the column, unless it's tilt. Teh blower runs through the accessory circuit on the ignition switch. If the switch is usually not the problem. Check the connector at the bottom of the column. If it's an original connector, it will probably show burning in the connector. If it does, cut that wire out and use two insulated male/female to rejoin it. This is a typical place for low voltage.
71F3, I have done the update you describe to the column wiring on my '70 without the tilt column. I have had the tilt/telescope column out of the '71 to replace the rubber shaft coupler and, though my recollection of the set-up is fuzzy, things were indeed different in the column wiring department (is this a Saginaw column?). As I recall, I saw no problems so I probably just cleaned the connectors and packed 'em with grease. I will check this wiring again and proceeed accordingly.
Actually, I have been using a voltmeter. The car has been parked for a while so battery voltage is down just a bit, but the values for the heater blower feed circiut are pretty consistently 1v to 1.5v lower than the battery. Thanks for all of the feedback.
And yes, Fury 440, I have both of the factory '71 manuals (not as user-friendly as the '70 Chrysler manual because it covers all '71 Chrysler and Plymouth) but thanks for the offer of a circuit diagram anyway.
I remembered that I have an NOS control head gathering dust, so I pulled it out along with my OHM meter and learned something. There are two semi separate circuits supplying voltage to the blower motor. One part is active when in an A/C setting and the other when in heat. Two supply wires run from the control head to the blower resistor block. They connect at two separate locations on block. I'm sure that there is extra resistance built in to the heat mode circuit. I don't have a blower motor resistor block to OHM out and get the values. The 1970 Chrysler Imperial service manual has a nice schematic on page 24-38 at bottom. Circuit 14T is voltage route in A/C mode. 14BR is used during heat and defrost. The engineers must have wanted different blower speeds between heat and A/C or else why would they have duplicated circuits. Hope this is some help. image attached (I hope).