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Old 02-26-2015, 08:22 AM   #26
tanman722001
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Re: 1988 k2500 defrost problem

I know this is a old post. But one link they was said a thumping noise. As i have. They say cuy to two wire why cut the wires. What to do after you cut them. Or is there a different fix.
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1991 GMC K2500 4X4 350/auto
1991 Chevy S10 ext cab.
1990 Chevy S10
1993 Chevy S10 Blazer 4dr 4.3 Vortex/Auto
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Old 02-26-2015, 11:46 AM   #27
ChevyTech
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Re: 1988 k2500 defrost problem

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Originally Posted by tanman722001 View Post
I know this is a old post. But one link they was said a thumping noise. As i have. They say cuy to two wire why cut the wires. What to do after you cut them. Or is there a different fix.
If you use the cut the wire suggestion, the actuator (motor) will no longer work. That will stop the noise because it no longer works.

That actuator is there to make the AC colder, when the recirculation door is closed. The recirculation door opens so the vehicle doors close easier, and it does not pop your ears when you shut the door. It is open more then it is closed. In the defrost mode it is needs to be open to bring dry air into the vehicle to keep the windows more clear.

If you have a truck and the AC does not work, you could unplug the motor so it does not make noise.
It is hard to get to so that is most likely why they said cut the wire.
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Old 10-03-2017, 12:38 PM   #28
88lowrider
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Re: 1988 k2500 defrost problem

I see this is a Old thread but not finding any updated information or more information about my problem. So, going to try here first. ChevyTech, you have always helped me in the past so, here goes.
1988 GMC C1500 Sierra, Gas V8 with EFI, auto trans, AC, had the fancy stereo in it that got replaced.
It has the fancy heater/ac controller in it so its I guess digital they might call it?
I will get a picture of the truck and the controls so I am not wasting anyone's time.

I had let the truck set for almost a year, outside. Started to bring the truck back as the price of the new ones were not possible, so, fixing this on my own the best I can. Just turned 70 but been a mechanic in my early year for two dealerships, both GM. Grew up in a wrecking yard taking things apart and building hot rods. I do understand Innovative fabrication and have had to be creative as most of my rigs are older. 91 Geo Tracker, 76 Dodge Van, 79 chev 1500 4x4, and my 88 GMC lowrider which the heater quit working.

I have been though this thread looking and all the links, printing out pictures of the heater design, location of the actuators and well, blah blah blah.

I think its best to show you what I have and the big question would be, How do you Test the Temperature Door Actuator motor ?

I have had the instrument cluster out and able to access to the heater/ac controller. The book just says how to Replace it, not test things.

I would like to test the heater controller as well as the actuator motor before I just start replacing expensive items.
Hope someone can help me please.
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Old 10-03-2017, 08:47 PM   #29
ChevyTech
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Re: 1988 k2500 defrost problem

Hi Lowrider.

This is from my notes and should help.

HVAC Temp door actuator testing

With everything connected, and the key on, the dark blue wire (which shows the position) with door at full cold should read about 4 volts. At full hot the Dark blue wire should have about .5 volt on it.

The light green and light blue wires are the power and ground to move the motor. It should show a voltage between 6 and 7.5 volts on these wires when the motor is trying to move the door position. The polarity depends on which direction the controller is trying to move the door.

Here is a link to a thread with a schematic in it for a 1994.
the 1988 system is different then an 1994. A 1988 thas a position sensor circuit for the recirc door and a 1994 does not. I would think there are other differences too.


http://www.truckforum.org/threads/ac...-silver.20021/
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For those of you that are wondering why you are not getting replies to your thread:
Did you give the model, year, engine, fuel system type, and transmission information?
If it is modified from what came stock from the factory, let us know that too.
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Old 10-04-2017, 09:52 PM   #30
88lowrider
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Re: 1988 k2500 defrost problem

Quote:
Originally Posted by ChevyTech View Post
Hi Lowrider.

This is from my notes and should help.

HVAC Temp door actuator testing

With everything connected, and the key on, the dark blue wire (which shows the position) with door at full cold should read about 4 volts. At full hot the Dark blue wire should have about .5 volt on it.

The light green and light blue wires are the power and ground to move the motor. It should show a voltage between 6 and 7.5 volts on these wires when the motor is trying to move the door position. The polarity depends on which direction the controller is trying to move the door.

Here is a link to a thread with a schematic in it for a 1994.
the 1988 system is different then an 1994. A 1988 thas a position sensor circuit for the recirc door and a 1994 does not. I would think there are other differences too.


http://www.truckforum.org/threads/ac...-silver.20021/
Wow, can't thank you enough. I searched and searched and never could find anything like this...

I stopped by the radio shop today and the fellow showed me how to remove the stereo as so to get behind the dash were that thing is.

I will let you know what I find :-)
Thanks again ChevyTech !!!
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Old 10-05-2017, 11:24 PM   #31
88lowrider
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Re: 1988 k2500 defrost problem

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Originally Posted by 88lowrider View Post
Wow, can't thank you enough. I searched and searched and never could find anything like this...

I stopped by the radio shop today and the fellow showed me how to remove the stereo as so to get behind the dash were that thing is.

I will let you know what I find :-)
Thanks again ChevyTech !!!
I think I need to take this back to my own thread and not be robbing this one.
Quick like, got the stereo and glove box out, checked the blue wire voltage, on low, 2.593 volts, on Hot, .638 volts, used a hose and made a Steth-a-hose and I could here that door motor working. No crunching or stripping gear sounds, then once it got to the end, clunk and stopped. Went back the other direction, same thing.
Then went to the air conditioner. Very cold air coming out on Low temp, moved it to High and noticed it was not as cold. I am guessing the door is working.
Reason I think it is was because I went out, put the fluke inferred on the thermostat housing, 178 degrees (can't seem to find a accurate thermostat, have tried three so far).
Then the stupid on my part. I forgot to check the heater hoses for heat

Found the hose at the radiator, quite cooler than expected, then felt the one coming off the back of the intake manifold, pretty warm but I had put on a "T" flush valve quite some time ago and well, once I felt on the other side, it was cool.

So, either I have a plugged line or the heater core might be plugged.
I will try to back flush it and see what comes out.
Oh, the radiator fluid level was above the heater hose line that comes in to it.

My fault, not checking the simple stuff first, sorry.
Helmar
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