1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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?

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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).

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

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

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Thanks, I tried to use the number shown and did not get anything to come up.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Got some more done, installed driver side A/C vent. This vent uses a plastic molded section that routes the vent duct below the steering wheel. You can see the plastic u shaped duct under the steering column. The duct that feeds the driver side vent also feeds the driver side right vent. Once these are installed you will need to position the driver side defrost duct and attach the end on the driver defrost outlet.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Next, positioned the right end of the center duct in the upper portion of the dash. Then move it aside and install the defrost door housing. Before installation I replaced the door foam seal. When installing the defrost door housing, connect the passenger side defrost hose going between the defrost vent and the housing. Defrost housing slides under two clips on the heater housing and is fastened in place by a screw on the right side. Connect the vacuum line to the actuator and then install the right end of the center duct using two screws one on each side. The center duct is held in position by two metal tabs with screws through the dash frame.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Here is a picture of the foam installed on the defrost door.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Installed the dash vents to the dash pad using six plastic nuts. Installed new foam seal on dash duct. Installed A/C Heat control, hooked it to both wire and vacuum harness. Note, I removed the radio before installing duct work to give me better access. Installed padded dash and instrument cluster bezel.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

nice job :D
amazed that gm had 2 firewalls for a truck ac and ac delete

why you didn't convert it over to r134?
all you had to do was solder in a new expantion valve
then go with a new compressor, dryer and hoses

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Thanks, yes I am planning on converting it, I have flushed the oil and have adapters to go on the low and high side ports. I am going to make new hoses that will be the barrier type for 134A.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Next I installed the A/C configured glove box. I had to change the plastic pocket from the donor door to my original door. This ended up being more difficult than I imagined. The lock has tumblers that have to be released. This is accomplished with a paperclip inserted into the hole in the release knob. Once the tumblers are released then you pull the knob and tumbler assembly out and remove the retaining nut using a hex wrench. Remove the four screws (2 each side) and bend the metal tabs on sides of the glove box door outer metal shell. This will give clearance so the plastic pocket will slide out. Reverse the process to install the A/C style pocket.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Installed the lower heater vent today. This vent is attached with a small screw on the passengers side and a bolt with rubber grommet on the drivers side. Note the forward edge snaps to the edge of the heater housing prior to installing the small screw.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Awesome write up, thanks for the level of detail!

-Richard

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Got some more done on the A/C conversion. I installed the vacuum controlled hot water shutoff valve. This valve stops the flow of hot water to the heater core when you select max cold on the temperature control. Settings other than max cold allow the heater core to operate to provide blend air for temp control.

I also got some more done on the interior. I installed a new dash pad and door cards. I purchased the door cards from LMC. They fit and look awesome.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

Did the dash pad also come from LMC? What color did you specify? That looks like what I need.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

No, I purchased it from Classic Industries, it is Carmine red. It fits real good as well. Just be sure to save your clips from the old one.

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

I need a new dash pad and door panels for my 77, and the original color looks like what you installed. I have been watching other people's projects to see how the look and where they got them before I buy any. Yours looks like the right stuff. Thanks!

Re: 1979 Chevrolet C70 Conversion to OEM Air Conditioning
 

1979 C65 really low mileage ex-firetruck. Looks like dealer add-on A/C, maybe this will help you.