heater only works on high....searched already

[xpndbl3]

My heater only works on high, I installed a new blower resistor as old posts that I searched for showed as solving the problem. It still only works on high and I installed an AC delco part not a cheap autozone one. Where should I go from here to fix this now? Could the switch be bad? Any wiring to check with a voltmeter?

 

[buefchris]

I've seen a few OEM switchs go bad in the early models.

 

[xpndbl3]

well guess I should have mentioned this is an 88 3/4 ton suburban if that matters. I figured I could go junkyarding for a different switch but didn't know if there was anything to test first.

 

[Yobtaf]

Mine is doing the same thing. Your better off going to vato zone or napa for the switch. I have a parts truck in my yard and took the one off of it to find out it doesnt work. A lot of work for nothing.

 

[xpndbl3]

just didn't want to blindly toss more money at it if there is some electrical to test first you know?

 

[Yobtaf]

I hear ya, I thought mine worked on all settings until I pulled the whole thing out and saw a spark. I think I hit the part on the back against the dash and shorted it out. Im not sure but I think thats what happened. Im actually hoping its the switch and not the block in the back that the sliding parts go into.

 

[noJeepshere]

My 81 did the same thing a few years ago, it was the switch in the dash that controls the fan speed. $10-15 part and if that isn't it, it is the resistor block that controls the voltage to the fan motor.

 

[Yobtaf]

is the resistor block the part that the controls go into?

 

[tRustyK5]

The resistor block is at the fan motor area, engine side. It's on top where it's easy to see and get to. you unplug it, then unscrew the screws holding the resistor block to the fan housing.

Rene

 

[Yobtaf]

The resistor block is at the fan motor area, engine side. It's on top where it's easy to see and get to. you unplug it, then unscrew the screws holding the resistor block to the fan housing.

Rene

got ya, thanks Rene

 

[xpndbl3]

I already replaced the resistor block, would the next logical step then be the switch? Or is there a wiring schematic to check first to see that it failed?

 

[noJeepshere]

Well if you really want to take the time to check for continuity in each wire in the fan control circuit, you can find a digital volt/ohm meter and do that, but I think that your switch has failed, based on past experience and that they tend to fail.

 

[xpndbl3]

Fair enough, guess I'll have to pull out the controls shortly and replace the switch and hopefully that'll get me back on track.

 

[noJeepshere]

Don't worry, it's easy, just take your dash apart. Unless it's like the dash in my 81 It's held in by a few screws, some electrical tape, and hope.

 

[rd2116]

I wouldn't replace the switch/control head just yet. There is also a relay wired in between the resistor and the blower motor called the high blower relay. I'm not sure of the exact location on an 88 suburban but it should be mounted inside the vehicle on the heater box, usually behind the glove box. When you find it you can test for power at the dark blue wire, according to the schematic (I can't post a link to the schematic due to this being my first post) with the key on and switch in low or medium fan setting. You can test with a volt meter or a bulb equipped (as opposed to diode equipped) test light. There should be less than 12 volts due to the power being fed through the resistor, probably in the range of 9 to 10 volts, or the test light bulb will be dimmer than normal. If there is power on the dark blue wire check for power on the purple wire coming out of the relay, power on blue and none on purple = bad relay. Hope this helps without having to just throw parts at it.
EDIT- It appears the relay is mounted on the heater box in the engine compartment. I will check on my 88 blazer in the morning to confirm the location.