1974 A/C Heater Core-Harrison Available?

[Paul L.]

The heater core on my 1974 with A/C went south yesterday and it started to drip on the passenger carpet. I was close to home thank goodness and most of the dump went down the vertical tubes onto the road. The coolant tank emptied as did much of 2" of rad. But all is cleaned up now and with no damage to the interior. No comment on what ethylene glycol on the local road contributes to global warming....

I subsequently cut the hoses to the core and bypassed it to keep the 1974 running (hose from waterpump to intake directly). No problem with this today and the car runs well and holds steady at ~200*F at 86*F ambient. But of course I wish to get this matter fixed before autumn. I am well aware of the time needed for this repair and the pain involved. So I wish to do it only once.

There are a myriad of A/C heater cores out there from $25.00 up. Is there a GM/Harrison unit still available that will install without fitment issues or leaks? I've seen threads on this matter and some of the Chinese units offered even by reputable Corvette vendors, maybe even Delco?, can be suspect. Any recommendations on a good choice? Or is having a rad shop re-do the original an option?

[Dick W.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul, I see cores advertised as manufactured by the OEM manufacturer. I am not sure who actually that is/was as I thought that Harrison was the manufacturer.

Another option is recoring your tanks. Always a slight risk as brass fatigues rather easily.

[Joe L.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul, I see cores advertised as manufactured by the OEM manufacturer. I am not sure who actually that is/was as I thought that Harrison was the manufacturer.

Another option is recoring your tanks. Always a slight risk as brass fatigues rather easily.

Dick and Paul-----


A heater core for Paul's application is available from GM under GM #52484060, aka Delco #15-60094. GM list is about 133 bucks, much less from Delco dealers.

This heater core is not manufactured by Harrison. Harrison has not manufactured these cores in many years. Some outside manufacturer has made them. In fact, the same manufacturing source might make them for all brands; they all appear the same, anyway. Nevertheless, I stick with GM/Delco on these regardless of whether they are the same as all others, or not.

As far as fitment goes. if your car has the original heater core in it, you will find that very slight modification of the heater box may be necessary to get the new core to fit. That's because the new cores are slightly different dimensionally than the originals. It will be obvious what needs to be done. It's very minor. If the heater core has been replaced previously, the chances are the modification has already been done.

You can identify an original (or, early SERVICE) core since it will have "Harrison" embossed on one of the tanks. The current GM/Delco replacement will not. However, once it's installed in the car, no one will ever know the difference (except the next guy that replaces it).

A heater core is something that you want to last as long as possible since it's time-consuming to replace it. So, I always use NEW GM/Delco.

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Joe and Dick,
Thanks for the replies. I will check with the local Delco shop to see if #15-60094 is available.

As alluded to, I only want to do this job once and don't mind paying for a premium part upfront. I checked with the GM/Chevrolet dealer and they would not even give me a Mitchell flat rate for the repair. They want straight time. I suspect they don't have anyone who has ever done the job. I'm not inclined to pay $100/hour for someone to experiment.

So I'll drive with the bypass in place and in a time of foul weather in future, set aside several days to do my own experimentation. Meanwhile I'll purchase the core if it is available.

*Edit* - The Delco people say the core is available from the USA. It will take about a week to arrive here in Ontario. The price is ~$130.00. Makes you wonder who is producing the $37 versions on EBay and what the quality is??

[Dick W.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul, I think that Mitchell's flat rate is somewhere around 3.7 hours.

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul, I think that Mitchell's flat rate is somewhere around 3.7 hours.

I would be willing to pay for that time but I don't think the GM dealer will agree to it. They say their books or I guess database do not go back to 1974 . I suspect they just don't want the job.

[Jim T.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul it is really not that hard to change the heater core in your 74 unless you are an impatient person and don't like to take your time. One thing you need to remember if you remove it is that there is one bolt that does not have a regular type head on it, not one you can put a wrench on, however on the opposite side of the inside, on the firewall engine side you will have to remove the (think its a half inch) nut for removal.
When I first looked at my 70 and saw how the heater tubes were vertical in the engine compartment behind the air cond housing, I wondered how I was going to remove it from the inside. It came right out with no problems from the inside my 70.
Be patient with the air cond ducting. Most likely you will only have to do this once.

[Joe L.]

Re: 1974 A/C Heater Core-Harrison Available?

I would be willing to pay for that time but I don't think the GM dealer will agree to it. They say their books or I guess database do not go back to 1974 . I suspect they just don't want the job.

Paul-----


I understand that there's a growing tendency of GM dealerships to turn down, as a matter of policy, service work if the vehicle is over 10 model years old. This includes the GM car lines which the dealership sells. Under this policy, if you were to go into a Chevrolet dealership with, say, a 1997 Corvette, they would refuse most service work (they'd probably do things like oil changes, coolant flush, etc., though).

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Jim,
What tool is needed to get that oddball fastener off?

Joe,
That is hard to believe...but I suspect you are absolutely correct. But refusing work on a C5 (1997)? Having a 1967 and now a 1974 I look on a 1997 as a "modern" car. I'm getting out of touch with the real world.

Re the heater core R&R I got these step-by-step instructions on another forum. They may be of assistance to C3 viewers here.

1. Remove the map pocket panel and kick pad and right side a/c duct.
2. Remove the center gauge cluster, wiper/ac vent plate.
3. Remove the radio.
4. Remove the center, lower, and upper air ducts. One of these will have a vacuum valve with two hoses. Make sure you mark the color of the hoses and where they go. If you put them on backwards the air will come out the floor when set of defrost and vise versa.
5. Remove the temp cable from the heater box. Also before you do this make sure the cable is free and when in the cold position it pushes the switch all the way in on top of the box.
6. Remove the vacuum hose going to the valve in the right kick panel
7. Remove the bolts from the heater box on the inside of the car.
8. Remove the nut on the stud out on the evaporator box in the engine compartment.
9. If I didn't miss anything lift the inside box up and out. When you do this there is another vacuum valve and two hoses on the backside of the box in where the center gauges would be. Becarefull not to break the hoses off.
10. The box is out of the car.
11. Now there are a bunch of little 1/4 bolts that need to be removed.
12. Also the stem where the temp cable was you will need to remove the bracket holding it on.
13. If you got all of the bolts the core should slide out of the case.
14. The core is held into its holder by two straps on each end and two bolts.
15. Some replacement cores will fit and some need you to file or trim the holder.
16 Install the core back in the case.
17. At this time make sure all of the vacuum valves are working. Lube them with WD40
18. Put the box back in the car hooking up the backside valve in the correct order. Make sure that no hoses or wires are pinched behind the case.
19. If the case is in the correct way install the nut out under the hood but don't tighten it all the way just a few turns so the case can't pop out.
20. Install the bolts holding the case to the firewall.
21. Install the upper, lower and center ducts, temp cable, and vacuum hoses.
22. At this point either install the heater hoses or loop them so you can start the car.
23. Start the car and set the control on a/c. The heater door should close and the air will blow out the center. Next set it on heater and the door should open the and the air shold come out the bottom, next set it on defrost and it should come out the top.
24. Check the temp cable and make sure it pushes the switch all the way in when set on cold. If it doesn't adjust the bracket on the switch.
25. If everything works to this point install the radio. Make sure the vacuum hoses coming from the controler on the console don't get pinched under the radio.
26. Install the center gauge cluster and start the car to make sure all gauges are working.
27. Install the right side air duct
28. Install the map pocket and kick panel
29. Install the seat
30. Tighten the nut out under the hood
31. Start the car and check for leaks and coolant level
32. YOUR DONE!!!!!

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Supplementary question while I await the new heater core. Just twigged to something. When I cut off the old hoses and discarded them there was no in-hose heater coolant control valve as I had in a former 1979. That one was vacuum actuated. This 1974 has A/C and I expected to see one. When A/C is activated what shuts off coolant flow to the core?

[Jack H.]

Re: 1974 A/C Heater Core-Harrison Available?

The hot water shut-off valve for A/C equipped Corvettes was an item that came and went over the various model years. If memory serves, it was on cars up through 1971, then 'disappeared' until it was returned in 1976.

The 'boogie' is the valve HAS to default to either being open or closed absent control vacuum. If the default isn't to being normally open, the threat is lack of heat and/or defrost should the system fail. That's potentially a safety threat, compared with simply not having the A/C work as efficiently as it might for 'creature comfort' summer driving.

So, when you get the car cooled down and make a short stop (fill up the tank, grab lunch, run into a store), the car bleeds vac, the valve opens and, by hot water convection, the heater core re-charges itself with heat. This means there'll be some residual heat in the air plenum until the car re-starts and the A/C begins the task of sucking heat out of the heater core once more....

So, for apparently cost saving reasons a 'cosmetic' component (the hot water shut-off valve) was deleted for a few years.

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Thanks Jack. Seems to be a flaw in engineering there somewhere. I may apply the "Home Depot" $12.00 solution as I did on my 1967 without A/C to reduce cabin heat.

[Jim T.]

Re: 1974 A/C Heater Core-Harrison Available?

Paul I am not home and can't look right now, believe it is an 1/2 nut on the engine side. It is easily seen looking from the top center of the air conditioning housing towards the passenger fender.

[Jack H.]

Re: 1974 A/C Heater Core-Harrison Available?

Yep, that approach gets the job done too!

[Paul L.]

Re: 1974 A/C Heater Core-Harrison Available?

Just an update as the heater core (Made in USA) arrived today. I ordered #15-60094. It appears that the parts #s have changed to GM 19131998 and Delco 15-63338. OR I am in receipt of the wrong core....