A/c Vir

[RMS73]

I have been 'fighting' with my 73 A/C system for several years. Found the big problem was a leak between the firewall and the fender allowing engine compartment air into the plenum. Now that is fixed I can not get the Max A/C temp down below 58. I noticed in a couple of y'all posts about adjusting the POA valve to get lower temperature out of the evaporator. Can the POA in the VIR be adjusted likewise? If so how?
Roger

PS
It is interesting to see many names that I used to see at CF.

 

[73 Mike]

I don't believe the VIR is at all adjustable but am interested in other points of view. I suppose you could increase the diameter of the orifice but I doubt that would be a good idea.

 

[010752]

Most of them can be adjusted despite GM's instructions. If using 134,
turn the little screw inside the end, (some had a 7/32 locknut) counter clockwise 1/2 to 1 turn. That should drop the pressure to 26-27 psi and bring you into the 40's.

These cars don't have a true recirculate, you will always be using ambient air, but you can sort of minimize it as Mr Vette did.
Properly you would have to remove the fender.

 

[mrvette]

Most of them can be adjusted despite GM's instructions. If using 134,
turn the little screw inside the end, (some had a 7/32 locknut) counter clockwise 1/2 to 1 turn. That should drop the pressure to 26-27 psi and bring you into the 40's.

These cars don't have a true recirculate, you will always be using ambient air, but you can sort of minimize it as Mr Vette did.
Properly you would have to remove the fender.

Interesting you say that, I just pulled the wheel yesterday, removed my fender liner patch, pulled the C4 motor to clean the evap housing....my system been on recirc I thought, for years....yet leaves still got into that housing....

can you explain, maybe a pix of where else that air is coming in from??

It rained pretty good today, so went for a drive with new top up to check weatherstriping for leaks.....and found some humid air got into the ducting somehow....I suspect from that suction/supply side of the fan....

:gurney:

 

[RMS73]

My 73 does have a true recirculation system. There is a vacuum door at the passenger kick panel that opens for recirc and a vacuum door in the cowl plenum that shuts against the plenum forcing the fan to pull air from the interior. When on regular A/C these doors reverse position and force the fan to pull in outside air from the cowl plenum. If the firewall is not sealed to the fender then engine compartemnt air will be forded in the samll plenum behind the passenger kickwall. When the A/C is in the recic mode then the hot engine compartment air will be mixed with the interior air. When in regular A/c
this hot air will push up into the cowl plenum and enter the fan.

Roger

 

[mrvette]

My 73 does have a true recirculation system. There is a vacuum door at the passenger kick panel that opens for recirc and a vacuum door in the cowl plenum that shuts against the plenum forcing the fan to pull air from the interior. When on regular A/C these doors reverse position and force the fan to pull in outside air from the cowl plenum. If the firewall is not sealed to the fender then engine compartemnt air will be forded in the samll plenum behind the passenger kickwall. When the A/C is in the recic mode then the hot engine compartment air will be mixed with the interior air. When in regular A/c
this hot air will push up into the cowl plenum and enter the fan.

Roger

Roger, anyone, can explain just where the firewall is open there??? high, lo, along the side?? I can't see anything much...but tempted to cut out some of the oval duct that old flapper door was in....make the thing bigger....is it possible to get at it? or will I have to cut some panels?? NOT cutting any fender over it, for sure....

:gurney:

 

[RMS73]

On mine the seal from at least the mid point down to the bottom appeared to have cracked. I have a small boroscope I put down into the side plenum. Then I took a shop light and held it against the point where the firewall meets the fender. Looking into the side plenum with my boroscope, actually it is a Ridgid SeeSnake I got at Home Depot, my helper could see the light coming into the side plenum. Turned the light off, no light in the side plenum, turned the light on, light in the side plenum. I got some foam weatherstripping, 2x2 for a window air condition seal to the window frame, at Lowes and pushed it into the seam between the firewall and the fender. Turned on the light and no light in the side plenum.

I discovered the hot air leak by measuring temperatures in the cowl plenum, side plenum, air ducts and found I was getting over 130F air temperature in the side plenum. The only place to get this hot of air would be from the engine compartment. That is why I did the light check.

Roger

 

[mrvette]

On mine the seal from at least the mid point down to the bottom appeared to have cracked. I have a small boroscope I put down into the side plenum. Then I took a shop light and held it against the point where the firewall meets the fender. Looking into the side plenum with my boroscope, actually it is a Ridgid SeeSnake I got at Home Depot, my helper could see the light coming into the side plenum. Turned the light off, no light in the side plenum, turned the light on, light in the side plenum. I got some foam weatherstripping, 2x2 for a window air condition seal to the window frame, at Lowes and pushed it into the seam between the firewall and the fender. Turned on the light and no light in the side plenum.

I discovered the hot air leak by measuring temperatures in the cowl plenum, side plenum, air ducts and found I was getting over 130F air temperature in the side plenum. The only place to get this hot of air would be from the engine compartment. That is why I did the light check.

Roger

Thanks, going to check that right now, in the dark of night....:crutches:

 

[big2bird]

On mine the seal from at least the mid point down to the bottom appeared to have cracked. I have a small boroscope I put down into the side plenum. Then I took a shop light and held it against the point where the firewall meets the fender. Looking into the side plenum with my boroscope, actually it is a Ridgid SeeSnake I got at Home Depot, my helper could see the light coming into the side plenum. Turned the light off, no light in the side plenum, turned the light on, light in the side plenum. I got some foam weatherstripping, 2x2 for a window air condition seal to the window frame, at Lowes and pushed it into the seam between the firewall and the fender. Turned on the light and no light in the side plenum.

I discovered the hot air leak by measuring temperatures in the cowl plenum, side plenum, air ducts and found I was getting over 130F air temperature in the side plenum. The only place to get this hot of air would be from the engine compartment. That is why I did the light check.

Roger

Thanks. I have a similar scope, and will check that also.