Hi All,

My vent temps aren't what they used to be so I did some t-shooting using my shop manual ('79). The temp blend door is working fine.

One of the tests (quick freon level check) states to use your hand to feel the temperature of the Evaporator Inlet pipe - (where it meets the Capillary tube) to see if that surface is warmer or colder than the Accumulator.

Well, the Evap. pipe is actually Hot where it meets the Capillary tube but the Evap pipe is Cold right where it comes out of the Heater Box. The only thing in between these 2 surfaces is that black-sticky goop (4 inches long) on the Evap pipe. The manual doesn't state what to do in this situation.
The only other clue that I have is that the compressor is always cycling - it never seems to shut off for a while.
Large line to compressor is ice cold and accumulator is ice cold.

thanks!

 

Could you clarify? It's "always cycling" as in turning on/off constantly? Or you mean it's pretty much always engaged?

 

do you have a set of gauges? what are the high and low side readings? the only way to diagnose properly is with gauges. Do a static test, then a compressor test and post your numbers...

 

need both hi and low side numbers

 

Remove a grill and clean the condenser....over the years they can become coated between the fins with dust/etc that isn't noticeable but affects cooling.

 

Yes, first make sure the AC "plumbing" and hardware is working.

What about the air plenum in the engine compartment? This is the plenum that feeds air to the evaporator. In my 70, it was about 1/4 to 1/3 full of dried leaves and air flow through the evaporator was severly blocked. This is a relatively common situation. On my BB 70, this plenum is about an inch from the passenger side exhaust manifold!!!! This manifold can probably reach 1000 degrees F and only the inch or so air gap and perhaps 1/4 inch of plenum wall plastic separates plenum air going into your evaporator coils from this extreme heat source. If you open the plenum to look for leaves, put some insulation in there. Also, have a look where the plenum is close to the exhaust manifold....on my 70, the exhaust manifold heat had destroyed the plastic in the plenum wall and there was a hole there!!

Covering the inside engine firewall with insulation is really good, but taking off the dashes, etc to get to the firewall is a BIG job. An underbody insulation system was sold for the 68 and 69 Corvettes. It was abandoned as a cost savings for the 70 and up cars. It's really not that expensive..the parts and pieces are still available..from Paragon for one source....and it's relatively easy to install. I know it fits the 70 cars..probably later models also. The factory 69 sidemount exhaust system will lower passenger compartment temperatures. It looks really great, but it is louder and now it's expensive...factory duplicate repro parts are still available...last time I looked the chrome plated shrouds were $2200.