Q) 94 ZJ Limited 4.0L blower motor relay

The HEVAC blower motor relay on my 94 ZJ Limited 4.0L without ATC appears to be failing. The fan motor will randomly shutdown then restart. Speed switch position is not a factor.

The specific location of the relay is a bit vague. Where does this relay reside?

Reply to
japeters
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Got enough R134 in there?

In the non ATC there isn't a relay, just the switch and a blower motor reistor pack that when it dies leaves you with high only.

From what I remember it's up behind the blower motor next to the firewall.

Reply to
DougW

The blower fan shutdown will occur with just the key in "Run" e.g. the engine is off but the fan circuit is live. AFAIK the A/C circuit is independent from the blower circuit.

The circuit diagram I have has a relay driving the speed select switch. I will scan and post. My guess for location given this layout is close to the control head.

Reply to
japeters

The blower fan shutdown will occur with just the key in "Run" e.g. the engine is off but the fan circuit is live. AFAIK the A/C circuit is independent from the blower circuit.

The circuit diagram I have has a relay driving the speed select switch. I will scan and post. My guess for location given this layout is close to the control head.

Reply to
L.W.(Bill) Hughes III

You don't have Automatic Climate Control right?

Remember I'm going off a 93 service manual here.

In the 93 (very close to the 94 as no major changes were made till 95) the only relay I show is in the ATC system schematic (HEVAC Module Wiring with ATC) and connects to the "power module".

For non ATC the Fan/Blower switch is just a wiper contact connecting a 14 Ga Dark-Green wire fed by Fuse 11 (30A) in the power distribution center behind the battery to one of several feeds that hit the resistor pack.

Tried pulling/cleaning/reinstalling the fuse? Could be a cruddy contact. Although stop-start-stop-start is more indicitive of a failing connector. Possibly at the fan?

Reply to
DougW

Non ATC, just 3 knobs: Speed, Mode and Temperature and A/C button.

I pulled both the resistor pack and blower fan connectors. No impact upon the shutdown other then if the fan was on it would stop while unplugged.

I will check the 40A fuse connection also, need to eliminate the obvious.

I can hear a relay click in the dash when it shuts down.

Reply to
japeters

Got me.

Mebby this will help.

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Reply to
DougW

I pulled the control head out of the dash today. The temperature control and blower speed switch harnesses both go to the right under the glove box. I also opened up the air bag relay cover in the glove box, but it does not provide any clues. Will be pulling the glove box for access to the top of the heater and A/C unit.

Pulling the temperature control connector from control head shuts down the fan, no surpise this is the "Off" function . The guage of the wires going into this connector is also smaller then the 14 for the speed control.

Reply to
japeters

The only thing that I can think of is if the motor itself has a breaker. I don't think it does, but who knows.

Got me.

Reply to
DougW

1994 JGC HEVAC Heater schematic,

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Reply to
japeters

What do you know, they did slide a relay in there. The rest is nearly identical. Wonder why the relay at that point?

Reply to
DougW

My guess is that the wiring harness was evolving into a common format between manual and ATC and/or they did not want 30A running through the mode control.

Reply to
japeters

Sounds reasonable. Perhapse there was a problem with that control burning out or they switched to a less expensive (less copper) version. That's got me thinking I should take a look at the mode selector just to make sure it's not melting. Shoving a relay in there would be easy, especially if it avoids problems.

Reply to
DougW

I had to replace an old one after it carbonized - like to never have gotten the connector off with those humongous wires to the switch. Instantly obvious what the problem was. FYI: the major issue of heating at high current contacts is most commonly corrosion. The contacts get an oxide coating which increases the resistance which increases the temp temp (to say the least) which weakens the spring force of the contacts which deceases the wiping force that removes the corrosion which...

Different problem but worth noting is that the sockets in your house do the same thing over time, especially if you plug in heavy loads. If the plug sags or falls out when you plug it in, REPLACE THE SOCKET NOW before the fire starts. No urban legend - I've seen it happen.

Reply to
Will Honea

:

Short answer: the relay is integrated into the fan speed switch.

This explains the "box" surrounding the controls in the heater schematic and no relay in the wiring diagram. I tested the relay solder tabs on the control and have isolated the fault there.

I will post a detailed photo of this switch.

The switch relay may be serviceable but I will need to price replacing the entire unit prior doing surgery.

Reply to
japeters

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