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Help!! my heater wont work and its cold



well short and sweet i got an 87 coupe- the other day went to use the heater/defogger and nada - zilch- nuttin happening- check fuses in right side dash panel-- (any more i miss?)- any ideas? or is this the end of my heater control panel any help will be apprciated--- thnx scott
Welcome To The Corvette Action Center a_scott_h!

First off, is it the fan that is not coming on, or is there no heat at all coming through the heater? Is the HVAC system electronically controlled or is it the manually controlled version? :confused

If it's the blower, there is a resistor assembly located atop the blower motor housing underhood, as well as a relay for the blower, the location of which escapes me at the moment. And the late hour prevents me from even thinking straight enough to find it in the books I have in front of me now. :crazy

Give us more details please.

:L I can't help myself! I just noticed in your profile that you are a "heating technician". And your Corvette is cold? :L
cold heating tech. ( lol)

yeah, i just realized it myself too bad i only fix oil fired heating systems lol- anyway- my problem isnt the fan though that doesnt come on either but there seems to be no power at the control panel (no lights) i have the manual (I think) its not the digital one it has the rear defogger switch on the right and the little lite- but that went at the same time thats why i think its power related or the whole control head is ng thnx for any help --scott
Ok Scott, I guess we'll have to direct this one to vigman (Mike). He is a wizard when it comes to the electrics on the C4s, and this sounds like it falls into that category. I've replaced my relay, switch and resistor, but haven't solved my glitch with my fan - it sometimes won't stay on in the "high" position. :eyerole

Good luck, Mike'll be here sometime today. ;)

_ken :w
Lights in A/C panel

There are not any indicators in the manual A/C
except the backlight of the panel
( night driving)

There are 2 fuses the A/C fuse 25 AMP & fuseible link K

The only indicator is for the rear window de-fog ( electric ) on the right side of the panel
( glows when on)

When you operate the controls do you hear the vac doors hissing & moving?

Psych..changed the post hahahahahahah
And Away we go! ( manual A/C only84-89)

I would check the following.

The blower relay located by the blower fan motor. almost on the top of the fire wall.

Get a test light.

Key on, engine off, *heater on, fan hi
( or select any other mode that suits you other than off and the TEMP lever dosen't matter)

At the relay check the following.

Red wire pin A +12 volts direct from the battery. this attaches to fusible link A
( that big jumble of red wires by the battery)..This is very important if this isn't hot you will not get High speed on the blower.

Orange wire pin D of the relay coil control
(is this HOT?)

This is the main output from the blower switch.

If this line is not hot we will have to pull the dash,or the 25amp A/C fuse is dead OR the switch in the heater control (under the slide levers) is toast..which is one of the bigger failures.

Dark Blue pin C of the relay ( with the fan switch 1 click down)

( Is this hot?)

This is the output of the blower resistors
so when you select the next slower speeds
this is the feed for the motor power to the blower.

Purple wire Pin E of the relay
Is this hot?
This is the output of the relay selecting between Max blower (Orange wire hot, coil pulled in +12 volts going directly to the fan) or your slower speeds via pin C ( relay relaxed)

If the purple wire is hot & your connections to the fan are cool...odds are your blower motor is shot.

Jump pin A (RED) to pin E (Purple)

If the motor's good & you have +12 on the red. The motor should spin.

If not
Check the ground G 109
on the frame leg under the AC stuff, black wire.


Thanks for helping Scott out with his problem Mike. :upthumbs

;) Tell me, what do you think would cause my blower to kick off after running for a while, then come back a little later.

Let me fill you in first I guess. At first I was getting no low speed fan, but had medium and high (or at least high - I can't remember now). I replaced the blower switch, it didn't make a difference. I replaced the relay and had high speed but no low speed, so I switched them back but it made no difference. Now I've switched 'em back and forth so many times that I lost track of which is which at this point, but the fact still remains that I'll have the high speed blower for a while, but then it kicks off and I only have low and medium for a while. I've looked at the resistors in the blower motor housing and they appear to be ok, so I haven't replaced those yet.

Any hints?

_ken :confused
Ken's problem

He loses High fan only after a while.

The middle 2 speeds seem ok
(replace your blower resistors while your there).

SO the power feed for HIGH speed is pin A
which is the +12 from the battery ( via fusible link K)

So you need to identify that link ( in the big pile of links by the battery)

Disconnect battery, remove all links, remove blower relay, get Ohm meter and buzz the line out between Pin A of the relay & the plie of links. Replace the link.

While your there pull the blower motor, remove the dead mice on the A/C condenser
& lube the motor.

Note here ( aka oh by the way)

there are secondary switches hooked up to the AC mode selector switch ( no not the blower switch)

This switch TOASTS.

The test is,
Put a test light on pin D of the blower relay.
Put the fan on HIGH
Slide the lever from MAX to NORM all the way down to defrost.

The test light should remain SOLID..If it flickers
the switch is getting FUNKY.

At this point..If you have the funk..replace the head unit.

no heat

thnx for the suggestions mike i will try them in the morning (2 AM NOW) my 25 amp is good --where is the fusible link fuse- and to answer your vac doors question -- no there is no noise - and u are right about which control head i have (just as u descirbed it) only
lited display is the rear wind/defog-----thnx again------ scott---- ill let ya know what happens :w
Also if you follow the wires back from the relay and blower motor they go to a connector under the A/C pipes. I had medium power and low but no high till I found the ground (black) wire in the connector was burnt. I cut the wires from the connector and put a waterproof splice on the ground and now the blower works as it is supposed to.
Foot note

When you have Burned wires, blown relays, toasted switches etc. It's a fair bet that the motor is getting funky.. but do not despair!!!

Take the blower motor out clean it & lube it!

While your there.. stick your hand in the blower hole & feel the AC evaporator grille.

You will find everything in the world in there from leafs to left socks.. get that funky gook OUTTA there and you will get more air flow & fewer odd smells!

You shoud have seen what came out of my Bronco..looked like black felt off a pool table.

heater still out

ok all thnx for the help so far but i still havent figured it out i believe its a power problem (since i dont have any at the control head) no blower no defogger nuttin --if it was just the heater id say ok maybe blower but the reaer window defogger went to same time------ the 25 amp fuse is good WHERE IS THE IN LINE FUSE?? HEEEEEEELP thnx again scott
Check your links

There are a bunch of Flexly red wires by the battery, follow the positive batt cable.

The Flexly red wires are the fusible links, there is a moulded round rubber/plastic thingy twds the end.( these are for other circuts.. not the one YOUR hunting)

To test, you have to get close to the splice point in the harness, the link sometimes goes close to the end where it's not so obvious.

Fusible link K for the fan HIGH is on the starter motor wiring harness. ( sorry you got to get under the car).

The power to the Heater & control assy is a brown on C-1 pin E this is a home run from the fuse panel. If ya got no juice here.. you'll have to check the fuse box out from the backside ( a big PAIN)

Try this..I didn't see your last SOS


Ah wait

You said the FUSE was good.. you didnt say that there was POWER to the fuse. And is there POWER to the DEFROSTER fuse????

Check the link under the starter.... Link K

The other ones are by the battery A,B,C,M,J,F&G.

It's a little black plastic cradle with a screw in the middle with all the flexy wires coming out.

Get a test light and poke em CLOSE to where they splice into the harness.

Link A is for the Defroster ( and others like brake, hatch etc.)

power splices

thnx guys will check first thing in the morning ----and let ya now-------scott
You need to use a test light and go to the fuse box and check for power to the fuses and circuit braker for the rear deffoger. The deffoger circuit braker(silver cased fuse in the fuse panel) should be the second one from the top is hot all the time the A/C fuse has to have the key on, but also check the gage fuse if it is blown the rear deffoger could not work either. Don't worry about the fusable link at this time you can check that by removing the relay and testing the heavy red wire with a test light but I would suspect a faulty relay both low and high have to go through it and I have found it to be the most likely problem for loose of blower motor operation other than motor. But check it out and let us know.

David Fulcher

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