Fan cuts out when on for a while

[Ross Wooldridge]

Hey all,

I think I know where to look, but it's going to be a PITA to do so.

Here's the symptom:

When I run the AC in my 66 T&C, it goes fine for a while, then all of a sudden, the blower stops. It might start again, then stops, start again, stop... and then it's done until the car cools down for a significant period of time. No electrical smell, no bad sound of labouring blower motor, nothing, it just stops. It also doesn't matter what speed I have the blower set to, so it's a main power before the blower motor resistor thing...

I think I need to check the actual blower motor switch in the dash. It gets 12V in, and directs it to one of 3 circuits (and the blower motor resistor) - low, medium and high (no resistor in the circuit). I assume the whole shebang is grounded through the blower motor's mounting to the firewall.

I started from the blower motor end of things, and checked the feed to the blower motor on the engine side of the firewall - tightened up the spade connectors and gave it a wire brushing, and did a sorta wiggle and check of the connections to the blower motor resistor under the dash. All those connections felt strong and there were no signs of corrosion or heat.

No change.

So therefore, I guess I must continue to work backwards and get to the dash switch. I guess I could work from the other end and check to see that 12V is actually getting to the switch from the circuit that feeds it - but I think I already know the answer to that, as the compressor stays engaged when the fan is stopped, so I know that 12V is getting to the HVAC controls - I just put it on Fresh Air and if I'm going down the road I get circulation of cooled air that way. As I write this I'm almost positive that I need to yank the switch and get some DeOxit in there.

Any sage words of advice? Am I on the right path?

 

[Davea Lux]

Hey all,

I think I know where to look, but it's going to be a PITA to do so.

Here's the symptom:

When I run the AC in my 66 T&C, it goes fine for a while, then all of a sudden, the blower stops. It might start again, then stops, start again, stop... and then it's done until the car cools down for a significant period of time. No electrical smell, no bad sound of labouring blower motor, nothing, it just stops. It also doesn't matter what speed I have the blower set to, so it's a main power before the blower motor resistor thing...

I think I need to check the actual blower motor switch in the dash. It gets 12V in, and directs it to one of 3 circuits (and the blower motor resistor) - low, medium and high (no resistor in the circuit). I assume the whole shebang is grounded through the blower motor's mounting to the firewall.

I started from the blower motor end of things, and checked the feed to the blower motor on the engine side of the firewall - tightened up the spade connectors and gave it a wire brushing, and did a sorta wiggle and check of the connections to the blower motor resistor under the dash. All those connections felt strong and there were no signs of corrosion or heat.

No change.

So therefore, I guess I must continue to work backwards and get to the dash switch. I guess I could work from the other end and check to see that 12V is actually getting to the switch from the circuit that feeds it - but I think I already know the answer to that, as the compressor stays engaged when the fan is stopped, so I know that 12V is getting to the HVAC controls - I just put it on Fresh Air and if I'm going down the road I get circulation of cooled air that way. As I write this I'm almost positive that I need to yank the switch and get some DeOxit in there.

Any sage words of advice? Am I on the right path?

It sounds like the circuit is heating up and going open due to high resistance someplace. Check the fuse connectors for rust. If that is ok, take a voltmeter and check the blower switch for high resistance.

Dave

 

[Big_John]

It does sound like a heat issue with something. I wouldn't rule out the blower motor though. It could be drawing so much current it overheats the switch etc.

 

[Devinism]

It wouldn't hurt to install a relay. I have seen plenty of the plastic push button switches with the blower terminals melted.

 

[rags]

any circuit breakers in the circuit or just a fuse?

 

[Sixpactogo]

I think you are on the right path. It sounds like a loss of continuity somewhere. If not in the power circuit, it could also be the ground wire from the motor to the firewall. Have you checked that?

 

[Ross Wooldridge]

It sounds like the circuit is heating up and going open due to high resistance someplace. Check the fuse connectors for rust. If that is ok, take a voltmeter and check the blower switch for high resistance.

Dave

I intend to check the blower motor for high resistance/high draw - but I'm not sure how to do that, and when I do, what would a number be to be considered high, and normal?

Thanks!

 

[Ross Wooldridge]

any circuit breakers in the circuit or just a fuse?

Nothing except what's factory at the moment. I am going to start from the fuse box and work my way towards the switch, and start at the blower motor resistor and work my way to the switch as well tomorrow. Getting that switch assembly out is a total pain, so hopefully something obvious will show itself before I have to go to that length.

 

[Ross Wooldridge]

I think you are on the right path. It sounds like a loss of continuity somewhere. If not in the power circuit, it could also be the ground wire from the motor to the firewall. Have you checked that?

Yes, I did, but I am going to check again.

 

[Big_John]

I intend to check the blower motor for high resistance/high draw - but I'm not sure how to do that, and when I do, what would a number be to be considered high, and normal?

Thanks!

I've never found a real accurate number for amperage draw. I have looked at this in the past and it looks like 10-11 amps is about average results for guys that have checked the draw.

I did find a spec once for newer cars and that's 15-20 amps... I doubt if it's that much for an older car with a 20 amp fuse, but I think it shows that 10-11 amps is in the ballpark.

 

[Big_John]

This might be worth a watch.

 

[Ross Wooldridge]

Thanks John! Sheesh - two issues crop up just as I'm getting ready for WPC. Figures, eh?

 

[commando1]

I have to disagree that it's a wiring problem.
Your symptoms, Ross, duplicates exactly what happens the line freezes up and shuts down until the line defrosts. This happens when coolant is low.

BTW, is your A/C compressor still the old RV2 with the EPR valve removed that is running 134 gas?

 

[Ross Wooldridge]

I have to disagree that it's a wiring problem.
Your symptoms, Ross, duplicates exactly what happens the line freezes up and shuts down until the line defrosts. This happens when coolant is low.

BTW, is your A/C compressor still the old RV2 unit that is running 134 gas?

Well, I wondered about that, BUT for the fact I still get compressor function, and the exap and rear AC unit still blows cold, and I and nice dry cold air out the dash when driving with the fresh air door setting on (Outside air forcing flow through the AC air pathway).

Blower fan on/off symptom is random - once the car is warmed up and the day is hot and I've been running the AC on for 30 minutes, the symptos start: the fan shuts off, and can come back on/shut off a few times until it's dead. Something electrical is opening up under load.

If refrigerant was low I would more expect the blower to keep going and vent air temps to rise and get humid "wet feeling" if the line and/evap were frozen up (which I've experienced before), but this is the opposite.

System is fully charged (using Butane-based stuff called Duracool). I've ben using that stuff without issue for about 10 years now. The system was serviced last year, and until this blower issue, performance has been stellar.

Thoughts?

 

[3175375]

Well, I wondered about that, BUT for the fact I still get compressor function, and the exap and rear AC unit still blows cold, and I and nice dry cold air out the dash when driving with the fresh air door setting on (Outside air forcing flow through the AC air pathway).

Blower fan on/off symptom is random - once the car is warmed up and the day is hot and I've been running the AC on for 30 minutes, the symptos start: the fan shuts off, and can come back on/shut off a few times until it's dead. Something electrical is opening up under load.

If refrigerant was low I would more expect the blower to keep going and vent air temps to rise and get humid "wet feeling" if the line and/evap were frozen up (which I've experienced before), but this is the opposite.

System is fully charged (using Butane-based stuff called Duracool). I've ben using that stuff without issue for about 10 years now. The system was serviced last year, and until this blower issue, performance has been stellar.

Thoughts?

If a floodback is happening, you should still hear and feel the blower working. You should also be able to see ice forming on the return line from the evaporator to the low side of the compressor.

I believe from what you have explained, there’s an electrical issue with the blower. Either the switch, wiring, electrical connection or the blower itself.

 

[rags]

I am going to start from the fuse box and work my way towards the switch

if you could catch it when it stops working, you could just follow the circuit with a test light and have your answer in minute. pulling the switch might be a pain but inspecting it could answer the question. is it accessible with an inspection camera? could it be left removed and operational so that the circuit could be checked at the switch when the problem occurs?

 

[Gerald Morris]

Pulling that switch shouldn't be a BIG PITA. Instead of pulling it, why don't you just BYPASS it temporarily to test your motor? That might save you considerable labor, or just a little. Having lived my entire adult life without automotive AC, I can't tell you much about that mechanism, but my electrical troubleshooting is good. That '66 should be controlled from a panel in the middle of your dash, and be reasonably accessible above, if you pull loose the radio, and below, if you can snake your arm up past the ashtrays. Then, find your switch, disconnect it, and either temporarily join the fan leads below, or use a proven switch to control them.

If this isn't a case of low freon, you can at least determine whether the blower motor is overloading or not. If Ma Par used resistors to shunt that motor for speed control, you may even easily bypass the switch for testing there more easily....

Just a few thoughts outside the icebox 4 ya.

 

[Ross Wooldridge]

Lol @Gerald Morris - you've obviously never dealt with pulling the switch on a 65 or 66 Chrysler - a totally different animal than a Dodge or Plymouth, or a 67 or 68 Chrysler for that matter... there's little to no room up in there. To even LOOK at the switch (which involves lying on your back with your head on the gas pedal and your feet over the seatback), the ash trays have to come out, AC and defrost tubes have to come out, steering column lower cover with fresh air vent cables and controls has to come out (which you then have to put under your head, which is uncomfortable to say the least), the AC vacuum switch, and its push buttons and tubes all have to come out ...and if one wants to actually pull the entire HVAC control unit, the radio should to come out, the speedo should come out for best access, it's a pain, believe me!

Regardless, I went through every single connection point in the chain, from fuse box to the blower motor.

Not a single piece of evidence of bad connections, overheating wiring, melting, nothing, nada. There were a couple of "loose" connections which I tightened up, but they were still OK by comparison to other connections. Blower motor resistor assembly was fine (I have an NOS one on standby, but it was OK), and yes, I can bypass all that to send a full unresisted 12V to the blower motor if I really need to...

Any connection I took apart I cleaned with emery cloth to ensure "new" metal to metal connection, and tightened up the female connectors.

I am now suspecting the blower motor - but why would it quit and come back, quit and come back? If it was going bad, wouldn't it just get worse and worse (slower) and just seize up and die?

Of course when I put it back together everything worked fine, and when I started the car (it's on jack stands to deal with the fuel leak issue) the temps dropped to meatlocker range in about 5 minutes of idling. The proof will be in the next time I drive it with the AC on for any length of time... so I don't know if I'll get to that before I head off to WPC next week, but I can send 12V directly to the blower if I need to.

I will report over the next couple of days. I am waiting on a fuel tank sending unit gasket.

 

[rags]

wouldn't it just get worse and worse (slower) and just seize up and die?

no. i gave it a 50/50 chance. you checked the connections on the outside of the switch but there are obviously internal connections (contacts) as well.

 

[Ross Wooldridge]

That's right - and I am not going to pull the switch at this point, as I have too much going on. I can deal with it after or during the winter.

So as I kind of understand, with no other evidence of overheat anywhere else, if the blower motor is pulling too much current in its attempt to keep going, the fan switch may have tired contacts inside it which are getting hot and opening up under load? Why would it do that on all speeds then?

I just don't see that - it's something where ALL the power going to the blower fan (after the switch and resistor) is getting interrupted, and from what I see that can only be the blower motor itself...

...OR...

I'm going to check the bulkhead connections for the feed to the blower motor again just to be sure.