ajrothm

I have slowly been working towards fixing my AC. Its a 1971, the system appears to be all original and intact. I talked to a few vette shops and they want to just rip out everything and install all new parts. I though, would like to test and trouble shoot it and only replace whats needed. I have a friend that does AC work and he says we can shoot some R22? into it, which is like a cheap refrigerate only used to search for leaks with the sniffer. If no leaks are detected, then drain it, vacuum the system and stick in the R12. I am sure we will have to change the POA valve but...

This past weekend I fixed all of the fan(blower) speeds and got it working along with all of the ducts. My compressor comes on but it just doesn't blow cold.

Here is my problem: I am getting heat into the AC system from the engine compartment. I know this has been an ongoing problem on old vettes. I just restored my interior, installed dynamat everywhere and I am CERTAIN the heat is coming into the AC system somehow and out through the ducts. Even if its 60* outside, I get 80-90*(at its coolest) air coming out of the vents. Here is what I have done so far:

1)Installed ball valve on the heater hose blocking hot water to the heater core.

2)Checked the hot/cold door in the ac box for proper operation and sealing. Appears to close off all the way and the gasket is still soft.

3) Checked the vacuum operated flapper in the pass. kick panel and it opens and closes when on MAX ac or not.

4) Checked my evaporator box for cracks or holes to let heat in. None

5) Checked my hood seal to make sure engine heat not getting into cowl area. Seal is good.

6) Sealed all holes that I could find in the firewall to cabin area.

7) Checked the other vacuum operated doors in the ac box that change over when control is moved from AC to heater etc and everything is working well.

SO any help in getting the hot air out of the system would be greatly appreciated. At this point, there is no use in charging the system and trying to get it to blow cold if I am still getting so much heat in the system from the engine compartment. Hell even if the ac blew 40* but its getting 100* heat mixed in with it, its futile.

Thanks in advance guys!

big_G

Two things to check....Make absolutley sure the ball valve is working (one of the heater hoses should be much hotter than the other). Next, make sure the hood weatherstrip is in good condition. This seal keeps the hot engine heat (and fumes) from getting into the HVAC inlet in the cowl. There will always be some heat absorbed by the heater/evaporator box. A working a/c system will overcome this. Not bad advice to at least pull the evap...we are currently doing the same on a '71 and the evap. was about 50% plugged with animal hair and other unidentifiable matter. Also, I hear that parallel flow condensers are more efficient when converting to R-134. Fab work and custom hoses would be required.

chevymans 77

Good advice G; here is what mine looked like.



Neal

ajrothm

Thanks Big G. Yeah I checked my hood seals and they are good. My ball valve was brand new and I checked to make sure it sealed. Plus my car runs REALLY cool, like right at 160* all the time so I don't think its heat coming from the heater core even IF water was getting to the core. The heat getting into the system is way more then just heat absorbtion through the e-box. I remember reading something about heat entering the system some how on the right side OUTSIDE of the car, there is some factory sealant there somewhere where air goes from the cowl into the system. I could not see what they were talking about though.

As I am driving down the road, the plastic ducting that feeds air to the left and right ducts gets almost to hot to touch with a bare hand. Last summer I stuck a thermometer in the duct and the out coming air was 110*, that was with the entire system turned off and the ball valve in place. There is something big letting engine compartment heat in there somehow. Somewhere by the blower motor or something I can't see.

I know these original systems don't work great but I would like to to work just so I can say it does and if I get caught in the rain, I have SOMETHING which is better then nothing. Going to aftermarket AC is not an option.

Thanks in advance.

427Hotrod

Just for fun I'd completely unhook the heater hoses and loop them together or whatever while you chase it down. I usually put two shutoffs in there..one on each line. While it doesn't circulate with one..you still get a lot of transfer.


Is the system working at all? Pressure readings? Or are we just getting rid of other heat before we mess with A/C??


JIM

mrvette

What is most likely happening is there is a flapper which is an absolute bitch to get to, up under the fender next to the cowling, there are 3? 1/4? inch bolts to get to it, on a bracket ONLY SEEN when you remove the wiper door completely....you will find a tiney hose going to that flapper door, it's what lets in outside air, and works just the opposite of the one under the kickpanel of the pass side....lovely....

so if one is open the other is closed......

IMO, after messing with this for years, the only way to fix the system to acceptable performance, is to remove the flapper under the fender, hard to do.....disable the spring/dashpot mechanism....line the door with RTV, and seal the damn thing shut permanently....then remove the interior door behind the kick panel....thus ensuring just the recirc postion....you got plenty of air exchange anyway....and enough heat loading regardless.....especially with a convertible like I have.....

NOW....you need make damn sure your blower is getting FULL system voltage when running on high speed.....the ground wire for the blower frame is too thin....I found it dropped over a volt with the full load....

THEN I found off this forum, to use a C4 blower motor and squirrel cage with 3/4 inch wooden spacer, this allows more airspeed,

obviously you need clean the air handler right in front of the evap coil....I do that though the blower motor hole with a 1.5 inch shop vac hose....suck all them damn leaves outta there, blocking the fresh air intake ensures it will never again get clogged, kinda hard to do with recirc position on the exclusive.....

the above fixes you airflow probelms for good....

ajrothm

Jim, I was kind of thinking about fixing the heat problem before dumping freon in and checking for leaks. I figured if an old system blows 50*s at best, yet I am getting 100* in the system already...its not gonna be worth fixing.

Thats a good idea blocking both heater hoses. I just stuck a valve in one because I figured if I stopped the circulation, it wouldn't get hot. I will look into looping them.

As for my system, it appears to be the original compressor and POA valve, as well as the condenser but the hoses look to have been replaced as they still look relatively new but I know they are at least 18-19 yrs old.

If I turn the AC on, the compressor kicks on yet nothing gets cold, no pipes or anything. Something is wrong though because the compressor stays on all the time, even if I put the control on "Vent" or on "HTR" the compressor still stays locked in. All wiring and relays for the blower appears to be original although I did have to repair a few wires and add new insulated female slide connectors.

Once I realized the extreme heat leaking in to the system,I knew it would be pointless to go further.

I want to keep the factory ac and want it to be liveable at least. I know it can be done, one of my buddies down here has a 77 and his AC was converted to R134 but nothing else was changed and is completely original and his blows 50*.

ajrothm

MR VETTE, that flapper you are talking about...thats EXACTLY what I was told about. That is where the air leaks in some how. I didn't know there was another flapper but....I know my flapper in the kick panel is working, not sure how well it seals off but...

To I have to take the wiper door off to get to it? I don't know if that flapper you speak about is working..I don't recall seeing a hose going to it maybe its disconnected and hung open? or closed? HMMMM

Some pictures would speak volumes to me...lol

I'm Batman

Did you take the box out with the engine in? I need to fix a hole in mine, but I'm not at a point where pulling the engine is an option. (I also want to cut and 'glas it for the deeper C4 fan.)

vettfixr

Read this. It may help.

https://www.corvetteforum.com/techti...=241&TopicID=3

ajrothm

Vettefixer. that was the thing I was thinking about. I have no idea how you got your hands in there to seal it, it would help if there were pics somewhere of this plenum and the flap up in it. I looked all through my 1970 chasis manual and there is no real pics only drawings of the flap valve. I wish I could see a cut away of the side of the car where this plenum is to give me an idea of where to seal before I rip my brand new dash apart. LOL

Very good read though and I am SURE thats where the air is coming in. I don't feel hot air coming in the kick panel vent though when driving, it seems like its all going in the ac box and out of the vents. With the AC off, my lower air valve flap should be open letting the hot air in the cab and I don't feel it coming in there.


I am gonna try to find some pics of that area. IF you happen to know of any, please advise. Thanks a lot for posting up on this thread...

Artsvette73

You don't have to remove the engine to get the evap out.Where the cqase splits you want to remove the half that is close to the engine. My 77 was loaded with debre. Might want to check the heater hoses that go to core the should be a seal ther to prevent engine compartment heat from getting in

I'm Batman

I need to get both halves out. I have a seal kit on hand to fix that problem.

vettfixr

Here's a pic of the problem area that someone gave me when they had their front clip off. Once you take the flapper off you can get your arm in there and seal the area in question. Notice on the picture how close the bottom opening is to the exhaust. By using a straw or two like I recommend you can maintain a drain without having a lot of heat sucked in to the system.

SIXFOOTER

This is the flap Gene was talking about. It may not be working. Also removing the evap is a good idea, mine looked just like the one above with all the leaves in it

BKbroiler

ajrothm - a minor point at the moment but, instead of valving off or looping your heater hoses, just remove the hoses and put pipe plugs in the water pump and manifold. I did this on my car. Also removes some clutter from under the hood. Good luck with the AC issues.

chevymans 77

It was one of those while I am at it, (had the motor out).

Neal

ajrothm

Thanks for all the replies guys...

Vette fixer, thanks a lot for the pic but i have a couple questions.
1) Where exactly do we need to apply the sealant in that area? Like where the plenum area seals to the firewall under blower? or right there where the fiberglass meets the front of the plenum area?

2) Also that flap in the pic, the rusty looking one, thats the same flap thats down in the kick panel area right? so where is the OTHER flap thats supposedly in the plenum that lets air in the cowl? I see the vacuum pod for one but, it the flap under it?

What I was looking for was a way engine heat could enter the AC system and I assumed it could get in the plenum and get pulled in by the blower but I never feel heat blowing in the kick panel area through the flap, at least no more then what you think would be normal. If heat was leaking in the plenum, would it not come into the cabin from the flap in the kick panel.

This is quite a mystery how the ac system works. I did study the original service manual but it had no real pics of how the air traveled through the plenum so I couldn't figure out how heat is getting in there. I don't think its coming in from the cowling under the windshield, at least not from the hood leaking.

ajrothm

Looking at my pic, is the area in red the area that needs to be resealed? also where I put the white line on the bottom where we should put the straw?

Is the area I have labled flap the actual cowl inlet flap?

ajrothm

Also, how does air enter the AC system? I know it comes in the cowl and the blower pics it up and blows it into somewhere? is there a hole on the other side of that vacuum pod/flap thing where air goes into the evap? I mean if its on MAX AC and the system is sucking air into the plenum from the cabin, where is it blowing it into?, around that top flap into the evap?

Sorry for the dumb questions, just trying to get an idea of how the system works so I can figure out where my heat leak is.

I don't have side pipes so I am unsure if my heat entry is this seal or not. I am kind thinking its getting into the evaporator box through the seams and seals, also maybe around the heater core. I am getting SERIOUS heat into the AC system somehow. not just a little warm air blowing in. All of my plastic AC ducts get over 100* surface temp. Almost as if the heater is on, even though the temp selector is on C, the whole system is turned off and the heat core is blocked out.