1960 Electra Losing A/C at stop lights

[Bill Stoneberg]

Is there a reason why A/C works great while driving but any time I put it under load or stop the car , the A/C continues to run but it no longer comes out the correct vents.  Its like losing vacuum in the car shuts the diaphragms.  Isn't that what  the reservoir under the hood is for ? Where can I find the check valve they talk about in the manual ?  Does it wear out or deteriorate ?

[NTX5467]

If it "quits cooling" when stopped, that can be an airflow through the condenser issue.

 

If it "quits cooling" under low engine manifold vacuum situations, the cool air might be coming out the defroster and heater ducts rather than the normal a/c ducts.  

 

There are multitudes of vacuum check valves.  Many reservoirs have an internal check valve to keep the reservoir "charged" so the vacuum doesn't go the wrong way.  If you don't find the one in the diagrams, you can consult the "HELP! rack" for one with the correct vacuum hose size.  Then check the "check" direction and install inline between the intake manifold and the vacuum reservoir.

 

The reservoir can have an additional function, too.  Damping the vacuum pulses in the manifold, so the a/c vacuum actuators and controls don't buzz or act funny at particular throttle settings.  That usually doesn't happen on GM products, though, but I've got another car that did that when I went to a heater water valve with a smaller vacuum chamber on it.  At certain lever settings and throttle amounts, the control would buzzzzz.

 

In the '60s, I don't recall any complaints about manifold vacuum issues causing poor a/c performance.  The GM/Harrison factory a/c systems normally chunked ice cubes no matter what.  And we had 70mph cruising speeds, too (even if not completely legal).  And "stop light grand prix" activities . . . even in big Buicks.  My uncle had a '60 LeSabre, lived near Houston, and after he finally found somebody that knew how to adjust the POA valve, NO complaints of a/c performance.  He liked to drive fast, too, as did his wife.

 

For general principles, have you checked the manifold vacuum with the car in "D" with the foot brake firmly applied, at base idle?  My Camaro would idle at 10.5" Hg and no issues of a/c performance, at idle of "under load".  Just curious.

 

NTX5467 

[Frank DuVal]

Check valves can leak, or systems can leak just enough to empty the reservoir when the engine has low vacuum.

 

However, idle usually has the best vacuum, develops against the closed throttle plate. So if the system does not work at idle, check vacuum with gauge first. 

[NTX5467]

In many of the older GM instrument panel controls, there is a rotary vacuum director, about the size between a quarter and half dollar in diameter.  It's held together by a flat clip and rotated via a lever on the control.  It is made of gray pot metal and the two sections are "metal to metal".  A small bolt holds it to the control structure along with a dowel for location, I suspect.

 

It could be that the mating surfaces have eroded with time and use, but I suspect they can be carefully "dressed" with some compound on a flat surface, then reassembled with a thin coat of thin lube.  Might just need a clean-up?

 

Something else I thought about later, but hopefully not a contributing factor.

 

NTX5467

[60FlatTop]

I am pretty sure that car runs a flooded evaporator. It should be checked by the book and not just given a shot of juice from the can of 12.

 

Both my '94 LT1 Roadmasters and my Impala SS blow hot air from the dash at sustained WOT, like for a mile at my favorite place. Makes me smile and I think here comes the heat. There is a little grove of trees in the median just after I let off where the real heat hides.

 

Bernie

[NTX5467]

(Any mutually-beneficial "calibration checks" lately, Bernie?)

[Bill Stoneberg]

11 hours ago, 60FlatTop said:

am pretty sure that car runs a flooded evaporator. It should be checked by the book and not just given a shot of juice from the can of 12.

 

Thanks Bernie,  When I filled it, I followed the book as written. When I go, it cools nicely.