1979 Chevrolet C70 Conversion to OEM Air Conditioning

[Airdirect]

This post will detail my conversion of a 1979 Chevrolet C70 from heater only to OEM Air Conditioning. This truck is equipped with a Detroit Diesel 4-53T and 5 speed trans with two speed rear axle. Just purchased this truck and plan to make it a flat bed hauler for my tractor collection. It has 45,000 original miles and is rust free.

[Airdirect]

Driving the truck home after purchase. This truck was last registered in 1989. The driver is Noah Jones, my son. We found the truck on Craigslist, was a non operating unit. Drove 850 miles one way to purchase it. With about six hours of work (brakes, lights and fluids) we were able to air up the tires and drive it back to Texas. Only problem we encountered in the 850 mile trip was a headlight failed. Stopped at O'Reilly and purchased a new sealed beam and we were back in business. We did not expect the tires to make the trip, we could not find a set of 9.00 X 20 in stock along our route. These tires are getting hard to acquire. The truck did not come with Air Conditioning. In Texas A/C is a must. I plan to document the conversion to OEM style A/C in this thread. Hopefully this will be of assistance to others who might want to do the same.

[Airdirect]

Here are pictures showing the modifications necessary to the cowl. The first picture shows my truck with heat only (I have already flattened the tabs), the second pictures shows a A/C equipped truck cowl. The first picture is taken from inside, the black line shows the area which will need to be opened for the A/C unit. The second picture is taken from the outside on a donor unit.

[Airdirect]

I was able to harvest the cowl insulation from the A/C donor which I used as a template to mark the opening and holes that would need to be drilled. I then fabricated a filler plate to close the heater only opening. This plate was then spot welded front and rear.

[Airdirect]

I then used a step bit to drill the heater hose holes and also drill the four corners of the A/C opening. During this process I also drilled the evaporator housing stud holes next to the dog house. I then used a jig saw to cut between the four holes to make the evaporator opening.

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The next step was to test fit the evaporator housing (no picture). I ended up having to elongate the two holes next to the dog house. With that exception it fit perfectly. Given this area is subject to lots of moisture, I elected to prime it and follow with 3M seam sealer. Once this is cured I will refinish with white topcoat.

[Katrina/10]

Nice write up, and nice truck! I did the same conversion on a 77, but it has a gas motor. What sort of compressor arrangement are you going to use on your Detroit? Glad you made the long trip safely, and hope you can find some tires.

[ckfarm]

As for the wheels,the best would be to change over to tubeless tires.You can buy a rim and tire for not much more than just the 900 20 tire. The equivalent wheel would be a7.25x22.5 with a10.00x22.5 tire.Or go to a 11x22.5 tire on a 8.25x22.5 rim as these maybe are more common.The wheels are a direct replacement,as the size difference comes in the way they are measured because of the different bead lip on a tubeless tire

[Airdirect]

Originally Posted by Katrina/10

Nice write up, and nice truck! I did the same conversion on a 77, but it has a gas motor. What sort of compressor arrangement are you going to use on your Detroit? Glad you made the long trip safely, and hope you can find some tires.

I harvested a GM compressor from a 1985 pickup. The pulley size is correct and I plan to drive it from the camshaft pulley on the front of the engine.

[Airdirect]

Originally Posted by ckfarm

As for the wheels,the best would be to change over to tubeless tires.You can buy a rim and tire for not much more than just the 900 20 tire. The equivalent wheel would be a7.25x22.5 with a10.00x22.5 tire.Or go to a 11x22.5 tire on a 8.25x22.5 rim as these maybe are more common.The wheels are a direct replacement,as the size difference comes in the way they are measured because of the different bead lip on a tubeless tire

Wow! Thanks for the valuable information and suggestion. You say the wheels are a direct replacement, do you mean the rims will fit my spoke wheels?

[ckfarm]

Yes they are the same. I should have said a 7.5 wide rim for the 10.00x22.5 tire not 7.25.Any good truck tire dealer should be able to set you up with no problem.

[jdl71]

Looking good so far. Sub'd. Just wondering though did you get a drive away tag from TX or the state you purchased it in? I've considered doing something like this, (though not for a big truck) and was wondering how to be semi legal.

[Airdirect]

I purchased the truck in Denver CO. In Colorado you can legally drive a vehicle with bill of sale and properly signed title for 36 hours. Must have these and proof of insurance with you at all times. For the remainder of the trip, I purchased a one way trip permit that allows me to drive a vehicle from a specific place to destination. Once you arrive it expires. Again you have to have proof of insurance. If you look in the pictures above you will see the one way trip permit in the back window.

[jdl71]

I saw the permit, that's what I was wondering about. Is it from TX or CO?

[Airdirect]

It was a Texas One Way permit that makes the vehicle a legal Texas licensed vehicle for the duration of the trip.

[57NAPCO]

Originally Posted by jdl71

Looking good so far. Sub'd. Just wondering though did you get a drive away tag from TX or the state you purchased it in? I've considered doing something like this, (though not for a big truck) and was wondering how to be semi legal.

Not that I suggest or condone doing this but over the last 25 years I've probably flew in one way and drove home at least 25 trucks from all over the country. Some never should have made it....not once did I ever drive one that was legally licensed. Most all had expired plates or no plates at all, never been pulled over or stopped.

[Airdirect]

Originally Posted by 57NAPCO

Not that I suggest or condone doing this but over the last 25 years I've probably flew in one way and drove home at least 25 trucks from all over the country. Some never should have made it....not once did I ever drive one that was legally licensed. Most all had expired plates or no plates at all, never been pulled over or stopped.

I prefer to be legal when I can. The one-way tag was cheap and having insurance was invaluable in my opinion. Would love to have had new tires, just feel very blessed that I did not have a problem. Praise the Lord.

[Airdirect]

Got more done on the conversion. Working around the air filter canister I decided to pull the filter and look at it. A sticker on the housing cautions to not over service the filter. Given the truck is a 1979, I don't think the previous owner can be accused of over servicing it. The filter date is Oct 1978.

The next item installed is the cowl insulation. Be sure to install the rubber plug (lower right corner) to hold the insulation is position.

[Airdirect]

Prior to installing the heater core housing (cab side), install the vacuum controlled vent on the right foot well. This provides the re-circulation vs fresh air function.

The next picture shows the heater system wire harness next to the A/C wire harness. Both harness plug into the same feed coming from the fuse box.

[Airdirect]

Once the cowl padding is installed and the wire harness is passed thru the cowling it is time to install the heater core housing (cab side). On the right side is a bolt that can be started to hold this housing in place while you install the evaporator housing (engine compartment side). Do not tighten this bolt until all the other bolts are installed.

The next two pictures show an area that I had to trim to give the evaporate clearance to align properly. If you look close just to the left of the heater core holes you will see a small tab that had to be removed.

[Airdirect]

Prior to installing the evaporator housing, apply sealant to the edges and the divider between the evaporator and blower.

[Airdirect]

Install the heater hose housing gasket between the cowl and the evaporator housing.

Once the evaporator housing is in place install the three nuts on thru studs and the three sheet metal bolts (two on fan housing and one on the top of the evaporator housing).

[Airdirect]

I replaced both heater hoses as the original hoses were too short to reach the relocated heater core. To gain access to the engine side of these hoses I had to loosen the alternator. The alternator belts were old and dry rotted. Looking at these belts, I am sure they are the original belts due to the GM number on the belts.

[Airdirect]

Does anyone have pictures of a OEM A/C compressor mounted on a 4-53T Detroit Diesel in this vintage truck. I am going to fab up a mount and would like to see what the OEM setup looked like.

Thanks.

[83GMCK2500]

I found reference to it on this page, no accompanying picture.