98 Gmc K1500

[gmnut1972]

this is a great site, I have a 98 k1500 pickup the heater control just became inop, the only thing that works is the fan switch, the temp dial inop, defrost,setting switchinop, a/c and recirc button inop also,

I pull out the control panel out and unhook, and check power at the plugs,hooked it back up and can get power from the fan switch,low med and hi with my test lite, but a/c and other controlds nothing,

anyhelp would be great thanks

[abracadabra]

this is a great site, I have a 98 k1500 pickup the heater control just became inop, the only thing that works is the fan switch, the temp dial inop, defrost,setting switchinop, a/c and recirc button inop also,

I pull out the control panel out and unhook, and check power at the plugs,hooked it back up and can get power from the fan switch,low med and hi with my test lite, but a/c and other controlds nothing,

anyhelp would be great thanks

 

If the 98 has a similiar control head to the 95, it may be a diode that has blown.  I had similiar symptoms on a 95, replaced the diode and all was well. GM will tell you the control head is not serviceable and wanted some ridiculous amount for a replacement. 

[gmnut1972]

this is a great site, I have a 98 k1500 pickup the heater control just became inop, the only thing that works is the fan switch, the temp dial inop, defrost,setting switchinop, a/c and recirc button inop also,

I pull out the control panel out and unhook, and check power at the plugs,hooked it back up and can get power from the fan switch,low med and hi with my test lite, but a/c and other controlds nothing,

anyhelp would be great thanks

 

If the 98 has a similiar control head to the 95, it may be a diode that has blown. I had similiar symptoms on a 95, replaced the diode and all was well. GM will tell you the control head is not serviceable and wanted some ridiculous amount for a replacement.

 

 

oh ok which diode is that? is it on the control panel

[abracadabra]

this is a great site, I have a 98 k1500 pickup the heater control just became inop, the only thing that works is the fan switch, the temp dial inop, defrost,setting switchinop, a/c and recirc button inop also,

I pull out the control panel out and unhook, and check power at the plugs,hooked it back up and can get power from the fan switch,low med and hi with my test lite, but a/c and other controlds nothing,

anyhelp would be great thanks

 

If the 98 has a similiar control head to the 95, it may be a diode that has blown. I had similiar symptoms on a 95, replaced the diode and all was well. GM will tell you the control head is not serviceable and wanted some ridiculous amount for a replacement.

 

 

oh ok which diode is that? is it on the control panel

 

it's been about 2 years since I fixed mine.  Found my original post from two years ago:

 

1995 Suburban HVAC Control Head is inoperative.

Air only from floor vents, irregardless of knob.

A/C light and clutch do not engage when button pushed.

Recirc light does not light when button pushed.

Fan speed works.

Rear defog works.

Fuses are all fine.

 

Found the following post by someone with similiar problems.

 

 

http://groups.google.com/group/alt.trucks....433057a3e1f2b1c

 

Unfortunately the control board is not labeled with designations.

There are 4 transistors on board labeled 4692, 4687, and 2857.

Looks like the 2857 one has overheated a bit. Does anyone have info on

what can be replaced on board to repair this?

 

Anyone else run across this problem?

 

Thanks.

 

 

No one replied :/  I ended up replacing the 2857 with a PNP transistor.  It's not a diode, it's a transistor.

 

http://www.fairchildsemi.com/pf/MP/MPSA56.html

 

The quote referenced above is:

 

Just fixed the A/C on my '95 1500 a few days ago. After a lot of 

searching, I found the attached message on www.chevytalk.org forums... 

His description of symptoms matched mine except that I have no rear 

defogger. Since my controls weren't exactly the same, the transistor 

wasn't quite as described. Maybe this info can help you, too. 

 

On www.chevytalk.org, search the forums for "a/c problem fixed" from all 

posts and you should find: 

 

* a/c problem fixed 

* #348460 - 02/26/03 07:38 AM  

* 

* Hi there! 

* I hope this info is valuable to someone perplexed by defect a/c. 

* 

* If you have following symptoms in your truck 

* 1) A/C button won't work 

* 2) Recirc won't work 

* 3) Mode of operation knob has no effect (air comes only to floor for 

* example) 

* 4) Rear defog button works normally 

* 5) Temp and fan speed knobs works normally 

* then you might have a similar problem I had. The fix is both easy and 

* inexpensive. Culprit is bad transistor Q1 on your control head. By 

* changing it (cost: 6 cents at Radioshack) everything works as usual. 

* Here in Finland GM dealer asks 275 Eur (about same in US dollars) for 

* the head, so there is your motivation to fix it by yourself. 

* 

* To take the head off, remove dash and gently slide the head out. 

* There are clips on both sides of the head, you need a screwdriver to 

* tweak them slightly inwards. Disconnect all cables. 

* 

* The transistor is MPSA56 (bipolar pnp) and you can locate the faulty 

* one easily. It is the one under the bracket just next to mode of 

* operation knob axis (NOT the easiest one at the edge of the board). 

* Install the new one to the other side of the board, so you don't have 

* to fit it into that extremely confined space. Make sure to connect 

* the legs to the right holes. Emitter, base and collector are marked 

* on the faulty transistor. 

* 

* If you have anything to ask, contact me and I'll send more 

* descriptive instructions. 

* 

* jari 

* 

* ----------- 

* Suburban -97 6.5TD, 73000 mi

 

Hope this helps.

[gmnut1972]

this is a great site, I have a 98 k1500 pickup the heater control just became inop, the only thing that works is the fan switch, the temp dial inop, defrost,setting switchinop, a/c and recirc button inop also,

I pull out the control panel out and unhook, and check power at the plugs,hooked it back up and can get power from the fan switch,low med and hi with my test lite, but a/c and other controlds nothing,

anyhelp would be great thanks

 

If the 98 has a similiar control head to the 95, it may be a diode that has blown. I had similiar symptoms on a 95, replaced the diode and all was well. GM will tell you the control head is not serviceable and wanted some ridiculous amount for a replacement.

 

 

oh ok which diode is that? is it on the control panel

 

it's been about 2 years since I fixed mine. Found my original post from two years ago:

 

1995 Suburban HVAC Control Head is inoperative.

Air only from floor vents, irregardless of knob.

A/C light and clutch do not engage when button pushed.

Recirc light does not light when button pushed.

Fan speed works.

Rear defog works.

Fuses are all fine.

 

Found the following post by someone with similiar problems.

 

 

http://groups.google.com/group/alt.trucks....433057a3e1f2b1c

 

Unfortunately the control board is not labeled with designations.

There are 4 transistors on board labeled 4692, 4687, and 2857.

Looks like the 2857 one has overheated a bit. Does anyone have info on

what can be replaced on board to repair this?

 

Anyone else run across this problem?

 

Thanks.

 

 

No one replied :/ I ended up replacing the 2857 with a PNP transistor. It's not a diode, it's a transistor.

 

http://www.fairchildsemi.com/pf/MP/MPSA56.html

 

The quote referenced above is:

 

Just fixed the A/C on my '95 1500 a few days ago. After a lot of

searching, I found the attached message on www.chevytalk.org forums...

His description of symptoms matched mine except that I have no rear

defogger. Since my controls weren't exactly the same, the transistor

wasn't quite as described. Maybe this info can help you, too.

 

On www.chevytalk.org, search the forums for "a/c problem fixed" from all

posts and you should find:

 

* a/c problem fixed

* #348460 - 02/26/03 07:38 AM

*

* Hi there!

* I hope this info is valuable to someone perplexed by defect a/c.

*

* If you have following symptoms in your truck

* 1) A/C button won't work

* 2) Recirc won't work

* 3) Mode of operation knob has no effect (air comes only to floor for

* example)

* 4) Rear defog button works normally

* 5) Temp and fan speed knobs works normally

* then you might have a similar problem I had. The fix is both easy and

* inexpensive. Culprit is bad transistor Q1 on your control head. By

* changing it (cost: 6 cents at Radioshack) everything works as usual.

* Here in Finland GM dealer asks 275 Eur (about same in US dollars) for

* the head, so there is your motivation to fix it by yourself.

*

* To take the head off, remove dash and gently slide the head out.

* There are clips on both sides of the head, you need a screwdriver to

* tweak them slightly inwards. Disconnect all cables.

*

* The transistor is MPSA56 (bipolar pnp) and you can locate the faulty

* one easily. It is the one under the bracket just next to mode of

* operation knob axis (NOT the easiest one at the edge of the board).

* Install the new one to the other side of the board, so you don't have

* to fit it into that extremely confined space. Make sure to connect

* the legs to the right holes. Emitter, base and collector are marked

* on the faulty transistor.

*

* If you have anything to ask, contact me and I'll send more

* descriptive instructions.

*

* jari

*

* -----------

* Suburban -97 6.5TD, 73000 mi

 

Hope this helps.

 

 

 

thanks alot i will take a look into thanks

Jason