I am helping a friend with a full sized 1996 Chevy truck. the heater
core is plugged and there is no air getting through it. Whats the trick
to getting the dam thing apart? got the fan out. there is four small
bolt on the heater fan housing top and bottom. removed those but the
housing wont come off. Got the bottom plenum housing loose below the AC
evap coil, but cannot get the back by the firewall to break loose.
Whats the trick?

also, the fan does not have high speed. the resistor pack is ok.
so is the HVAC control head (swapped parts). is there a relay somewhere
to do this?

bob

bob urz wrote:
> I am helping a friend with a full sized 1996 Chevy truck. the heater
> core is plugged and there is no air getting through it. Whats the trick
> to getting the dam thing apart? got the fan out. there is four small
> bolt on the heater fan housing top and bottom. removed those but the
> housing wont come off. Got the bottom plenum housing loose below the AC
> evap coil, but cannot get the back by the firewall to break loose.
> Whats the trick?
>
> also, the fan does not have high speed. the resistor pack is ok.
> so is the HVAC control head (swapped parts). is there a relay somewhere
> to do this?
>
> bob

Well bro in law managed to pry it out. the core was caked with garbage
so much that air flow through it was nil. He did crack a chunk of the
plenum while he was at it.

I think i got the high speed issue solved too. On some Gm trucks, the
High speed blower setting goes through a separate relay above the plenum
and blower motor. A different relay was no help. First, i determined
that the relay was not engaging with the speed selector switch on high.
The switch was ok, i had 12 volts there on high position, there was a
small connector with 4 or six smaller wires that this circuit goes
through that had a problem. I took the connector apart and work it and
the relay clicks now. Its clicks, but still no blower. further testing
with the fluke showed no power to the relay switched terminal.
I did not have a shop manual, but a little sleuthing showed this feed
went through a 3 pin connector at the bottom of the plenum and then
through the firewall. Close inspection showed it melted some. I could
not get it apart, but after working it i had the hot 12 volts back to
the relay. a new connector or bypass with a butt splice should fix it.
Seems a lot of people have this problem, but i had not seen this fix
mentioned.....

bob


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"bob urz" <sound@inetnebr.com> wrote in message
news:1214891191_10993@isp.n...

>
> Well bro in law managed to pry it out. the core was caked with garbage so
> much that air flow through it was nil. He did crack a chunk of the plenum
> while he was at it.
>

Brother-in-law or not Bob, I'd make him buy me a new truck for breaking that
piece.

> I think i got the high speed issue solved too. On some Gm trucks, the High
> speed blower setting goes through a separate relay above the plenum
> and blower motor. A different relay was no help. First, i determined
> that the relay was not engaging with the speed selector switch on high.
> The switch was ok, i had 12 volts there on high position, there was a
> small connector with 4 or six smaller wires that this circuit goes through
> that had a problem. I took the connector apart and work it and
> the relay clicks now. Its clicks, but still no blower. further testing
> with the fluke showed no power to the relay switched terminal.
> I did not have a shop manual, but a little sleuthing showed this feed
> went through a 3 pin connector at the bottom of the plenum and then
> through the firewall. Close inspection showed it melted some. I could not
> get it apart, but after working it i had the hot 12 volts back to the
> relay. a new connector or bypass with a butt splice should fix it.
> Seems a lot of people have this problem, but i had not seen this fix
> mentioned.....
>

Good sleuthing Bob. The AC relay is generally one of the first places to
look for the no high speed problem, but I had not heard about any
connector/wiring problems. That kind of tracing can get nasty and it's good
to see info like this to keep for future reference.

--

-Mike-
mmarlowREMOVE@alltel.net

Mike Marlow wrote:

> "bob urz" <sound@inetnebr.com> wrote in message
> news:1214891191_10993@isp.n...
>
>
>>Well bro in law managed to pry it out. the core was caked with garbage so
>>much that air flow through it was nil. He did crack a chunk of the plenum
>>while he was at it.
>>
>
>
> Brother-in-law or not Bob, I'd make him buy me a new truck for breaking that
> piece.
>
>
>>I think i got the high speed issue solved too. On some Gm trucks, the High
>>speed blower setting goes through a separate relay above the plenum
>>and blower motor. A different relay was no help. First, i determined
>>that the relay was not engaging with the speed selector switch on high.
>>The switch was ok, i had 12 volts there on high position, there was a
>>small connector with 4 or six smaller wires that this circuit goes through
>>that had a problem. I took the connector apart and work it and
>>the relay clicks now. Its clicks, but still no blower. further testing
>>with the fluke showed no power to the relay switched terminal.
>>I did not have a shop manual, but a little sleuthing showed this feed
>>went through a 3 pin connector at the bottom of the plenum and then
>>through the firewall. Close inspection showed it melted some. I could not
>>get it apart, but after working it i had the hot 12 volts back to the
>>relay. a new connector or bypass with a butt splice should fix it.
>>Seems a lot of people have this problem, but i had not seen this fix
>>mentioned.....
>>
>
>
> Good sleuthing Bob. The AC relay is generally one of the first places to
> look for the no high speed problem, but I had not heard about any
> connector/wiring problems. That kind of tracing can get nasty and it's good
> to see info like this to keep for future reference.
>
Well, it not my truck Its for a friend of ours that runs a tow truck
and salvages cars. Its on the tow truck. we got it back together, ALMOST
done. first, the low speeds blew the fuse when it was put back together.
bro in law pried off the screen from the evap coil when he replaced it
and forgot and left it in the plenum. this screen then
shorted out the blower motor resistor pack to ground. whoops.

So now, all the speeds work and the plenum is back together.
got my vacuum pump out and sucked down the system for a couple of
hours. Went to fill it and could not get the compressor to come on.
hot-wired the low side switch, no go. tried a different AC relay,
no go. I hot wired the relay to get the compressor to go and fill it
with R134. seems to be cooling ok.

further testing showed that i do not have ground at the fuse box under
the hood for the relay for the AC. the rest of the relays next ot it
seem to be working ok. So my mission now, is the ground somehow
separate, or where is it really connected to ground from the ac
relay on the main fuse box?

I ran out of time, and taking the fuse box loose seems to be somewhat
of a pain in the ass operation. If anyone has the factory shop manual
on this and would care to enlighten me before i tear the fuse box off
all help would be appreciated. What i need to know is where the small
ground wire from the ac relay socket grounds at? all this wire does is
complete the circuit to the AC relays coil. not a high current wire
at all.

Bob






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bob urz wrote:

>
> further testing showed that i do not have ground at the fuse box under
> the hood for the relay for the AC. the rest of the relays next ot it
> seem to be working ok. So my mission now, is the ground somehow
> separate, or where is it really connected to ground from the ac
> relay on the main fuse box?
>
> I ran out of time, and taking the fuse box loose seems to be somewhat
> of a pain in the ass operation. If anyone has the factory shop manual
> on this and would care to enlighten me before i tear the fuse box off
> all help would be appreciated. What i need to know is where the small
> ground wire from the ac relay socket grounds at? all this wire does is
> complete the circuit to the AC relays coil. not a high current wire
> at all.
>
> Bob
>
>
>
>
>
>
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It's ground controlled. By the pcm.