Installing Air Conditioning on a Non Air Conditioning Truck

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Matt98

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Hi,
I am posting this to show what has to be done in order to install A/C on a GMT400 that did not come with A/C. I wanted to keep the manual climate control, with cables and do the swap as cheap as possible (basically free). Here's a basic write up of what I did. The total swap took me a day, minus pulling the dash out of the donor truck the night before (about an hour). I used the original non-AC HVAC box.

I used parts from a 98 Tahoe and swapped them into a 1992, so there were some differences, however it did pretty much bolt right in. I had to change the accessories to the 98 on the front of the engine. Unfortunately, I've swapped intakes since which would not clear the A/C compressor and had to remove it for now and return back to the original accessory setup, though I'll be putting a 92 style compressor and lines in and be back in business. Unfortunately, I didn't take any pictures of the swap, however I can explain what had to be done.

The HVAC boxes between the two trucks (Manual W/O AC, 92) (Auto climate W/ AC, 98) were identical, the piece that bolts to the passenger side of the AC box was different for recirculate. I was originally going to 3d print a lever to go on the 98 door so my passenger vent control could control recirc, but instead I decided to just use the entire original manual HVAC box. You will retain the fresh air vents this way, however you would lose recirculate without a bit of modification to the box. I didn't bother as I have a single cab truck anyhow, and it hasn't been an issue.

Start by pulling the dashboard from the truck, then the HVAC box. You will then need to disassemble the box to get where the evaporator would be. Mine had a rubber plug where the lines would run. With it apart, re-install the box. You can then get in the side with a sharpie and draw out the shape of the hole to drill in the firewall. Note that the hole is significantly larger than the line and there is a foam part that wraps around the evaporator and takes up the empty space in the hole. If you haven't pulled the evaporator from the donor truck, you will need to make this piece. Install the evaporator and re-assemble/install the HVAC box and the dashboard.

Next is the accumulator. I would recommend replacing this, however I re-used the one off the donor truck, and the bracket that holds it bolted right in. Install the compressor off the donor truck, again, it will bolt right in. Like I said, because I was using a vortec style compressor on a TBI style bracket, I had to switch the brackets, power steering pump, alternator, tensioner and the compressor.

To install the condenser, pop the grill off and it slides right in. You will need the mounting brackets, though for me the holes were already there, again, bolt in.
Next is to install the lines as they were. I would suggest replace the o-rings and orfice tube before installing the lines.

Next is the electrical. 95+ trucks use the BCM to control the compressor and all climate control, while 88-94 use the module. In my case, I was using neither as I was using the manual controls. Here is the simple understanding:

In the open "IGN" port on the convenience center, I installed a 10A fuse inline and ran a wire to a relay I installed under the hood to pin 30. I also ran a jumper wire off pin 30 to pin 85. Pin 30 will provide power to the compressor, and pin 85 will provide power to the coil in the relay. Next you want to install a switch in the dash. One end of the switch will simply go to ground, the other wire will run into the engine bay.

There are 3 switches (at least in my case with the vortec setup). There is a low pressure cut off switch, a cycling switch on the compressor and a 3rd which I believe is a safety switch if the pressure went too high. I never hooked up the high switch, as it didn't seem to function anyhow.

Run the wire from the switch you just pulled through to one side of the low pressure switch (on the accumulator), it does not matter which side you put the wire on. Take the other wire from the low pressure switch and run it to the (high pressure switch first if you've hooked it up, then to) cycling switch on the compressor. Finally you will take the other wire off the cycling switch and put it to pin 86 on the relay.

So now, when all conditions are correct (Switch is on in the truck, pressure is adequite) the relay will energize. The final pin on the relay (87) now needs to be run to one of the wires on the compressor clutch, again, it does not matter which one. The other wire on the compressor will go to ground.

Assuming everything is done correctly, the system can now be vacuumed, leak tested and charged. You have maintained the OE manual climate controls and the system will cycle as intended from factory. Note if you are charging it yourself that GM trucks (even new ones) have a low pressure cut off of 25PSI. When charging the system it will cycle a lot until you've put enough in that it will not drop below that amount.
 

1998_K1500_Sub

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When charging the system it will cycle a lot until you've put enough in that it will not drop below that amount.

Charging with liquid to the extent possible, once the system is “vacuumed” completely and with the compressor off, mitigates the extensive compressor run-time you described, but charging with liquid must be done thoughtfully and carefully. Just keep this approach on your radar.
 
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Kutthroat

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Hi,
I am posting this to show what has to be done in order to install A/C on a GMT400 that did not come with A/C. I wanted to keep the manual climate control, with cables and do the swap as cheap as possible (basically free). Here's a basic write up of what I did. The total swap took me a day, minus pulling the dash out of the donor truck the night before (about an hour). I used the original non-AC HVAC box.

I used parts from a 98 Tahoe and swapped them into a 1992, so there were some differences, however it did pretty much bolt right in. I had to change the accessories to the 98 on the front of the engine. Unfortunately, I've swapped intakes since which would not clear the A/C compressor and had to remove it for now and return back to the original accessory setup, though I'll be putting a 92 style compressor and lines in and be back in business. Unfortunately, I didn't take any pictures of the swap, however I can explain what had to be done.

The HVAC boxes between the two trucks (Manual W/O AC, 92) (Auto climate W/ AC, 98) were identical, the piece that bolts to the passenger side of the AC box was different for recirculate. I was originally going to 3d print a lever to go on the 98 door so my passenger vent control could control recirc, but instead I decided to just use the entire original manual HVAC box. You will retain the fresh air vents this way, however you would lose recirculate without a bit of modification to the box. I didn't bother as I have a single cab truck anyhow, and it hasn't been an issue.

Start by pulling the dashboard from the truck, then the HVAC box. You will then need to disassemble the box to get where the evaporator would be. Mine had a rubber plug where the lines would run. With it apart, re-install the box. You can then get in the side with a sharpie and draw out the shape of the hole to drill in the firewall. Note that the hole is significantly larger than the line and there is a foam part that wraps around the evaporator and takes up the empty space in the hole. If you haven't pulled the evaporator from the donor truck, you will need to make this piece. Install the evaporator and re-assemble/install the HVAC box and the dashboard.

Next is the accumulator. I would recommend replacing this, however I re-used the one off the donor truck, and the bracket that holds it bolted right in. Install the compressor off the donor truck, again, it will bolt right in. Like I said, because I was using a vortec style compressor on a TBI style bracket, I had to switch the brackets, power steering pump, alternator, tensioner and the compressor.

To install the condenser, pop the grill off and it slides right in. You will need the mounting brackets, though for me the holes were already there, again, bolt in.
Next is to install the lines as they were. I would suggest replace the o-rings and orfice tube before installing the lines.

Next is the electrical. 95+ trucks use the BCM to control the compressor and all climate control, while 88-94 use the module. In my case, I was using neither as I was using the manual controls. Here is the simple understanding:

In the open "IGN" port on the convenience center, I installed a 10A fuse inline and ran a wire to a relay I installed under the hood to pin 30. I also ran a jumper wire off pin 30 to pin 85. Pin 30 will provide power to the compressor, and pin 85 will provide power to the coil in the relay. Next you want to install a switch in the dash. One end of the switch will simply go to ground, the other wire will run into the engine bay.

There are 3 switches (at least in my case with the vortec setup). There is a low pressure cut off switch, a cycling switch on the compressor and a 3rd which I believe is a safety switch if the pressure went too high. I never hooked up the high switch, as it didn't seem to function anyhow.

Run the wire from the switch you just pulled through to one side of the low pressure switch (on the accumulator), it does not matter which side you put the wire on. Take the other wire from the low pressure switch and run it to the (high pressure switch first if you've hooked it up, then to) cycling switch on the compressor. Finally you will take the other wire off the cycling switch and put it to pin 86 on the relay.

So now, when all conditions are correct (Switch is on in the truck, pressure is adequite) the relay will energize. The final pin on the relay (87) now needs to be run to one of the wires on the compressor clutch, again, it does not matter which one. The other wire on the compressor will go to ground.

Assuming everything is done correctly, the system can now be vacuumed, leak tested and charged. You have maintained the OE manual climate controls and the system will cycle as intended from factory. Note if you are charging it yourself that GM trucks (even new ones) have a low pressure cut off of 25PSI. When charging the system it will cycle a lot until you've put enough in that it will not drop below that amount.
I'm thinking about doing this myself well written up it's making me believe that I could do it but I have a question idk if you could help answering... i have 95 non ac truck It's a 305 5.0 with manual transmission I found a 95 that's auto but it has a 350 4wheel drive are the wiring harnesses the same? Could I just take the wiring harness and hvac box with all the ac parts and just install it in mine? Or would there be need for me to do stuff to the computer to make it work??
 

Matt98

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I'm thinking about doing this myself well written up it's making me believe that I could do it but I have a question idk if you could help answering... i have 95 non ac truck It's a 305 5.0 with manual transmission I found a 95 that's auto but it has a 350 4wheel drive are the wiring harnesses the same? Could I just take the wiring harness and hvac box with all the ac parts and just install it in mine? Or would there be need for me to do stuff to the computer to make it work??
You should be okay. I had the entire unit out of the 98 I was originally going to swap in and managed to wire it up and have full function of all actuators etc. The only reason I didn't end up using it is because I wouldve had to make a custom control switch so it didn't look out of place in the older style dash. You may have to make some modifications to the wiring, as it may or may not use the computer to signal the a/c relay on, but the controller will work on its own
 

Kutthroat

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You should be okay. I had the entire unit out of the 98 I was originally going to swap in and managed to wire it up and have full function of all actuators etc. The only reason I didn't end up using it is because I wouldve had to make a custom control switch so it didn't look out of place in the older style dash. You may have to make some modifications to the wiring, as it may or may not use the computer to signal the a/c relay on, but the controller will work on its own
I ended up finding a 95 farm truck [same year as mine] for 600$ i removed the whole under the dash wiring harness and hvac box from it all I have left is the engine wiring harness part the only difference is my truck is a 305 manual 2 wheel drive and this truck is a 305 auto with 4x4 do you think it'll be any problems I should be able to just swap it out plug and play?
 

Matt98

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I ended up finding a 95 farm truck [same year as mine] for 600$ i removed the whole under the dash wiring harness and hvac box from it all I have left is the engine wiring harness part the only difference is my truck is a 305 manual 2 wheel drive and this truck is a 305 auto with 4x4 do you think it'll be any problems I should be able to just swap it out plug and play?
Now that I think about it, when I was originally going to use all the controls I cut the wires I needed from the harness and rewired it to make it a stand alone harness. That is possibly what you will have to do. I would assume it would fit if you were to swap the entire harness, maybe someone else can chime in. It was completely different for me because my truck is a 92 with cable actuators.
 

iamthesargent

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I've been looking at adding air conditioning to my non-ac truck, and this seems promising to say the least. I do have to wonder, is this setup having to fight with the heater core as well (Not sure if thats how Factory Air HVACs did this too)? And without any dash vents, are you running the cool air through the floor vents?
 
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