Suction Throttle Valve vac source?

[Dan M.]

My 64 A/C coupe has problems. Anew compressor installed , high side has good pressure, low side has 20 inches vacuum. Mechanic says restriction somewhere, probably expansion valve. I'm trying to determine if the STV is working properly or if it is the plug. Can anyone tell me an easy way to test the STV on the car or off. And I also need to know where the vac line feeding the Atmospheric regulator comes from. Right now it is teed off manifold vacuum. Is this correct? Are there any companies that can rebuild the exp valve or STV if needed? Thanks for the help. Dan

[Edward J.]

Re: Suction Throttle Valve vac source?

Dan, Did something in the compressor fail?, generally when a compressor fails all the debris tends to block up the screen on the STV or the valve its self gets stuck causing the system to go into a vaccum on the low side.

If the compresssor did fail and system was not flushed and receiver dryer not replaced, the compressor will be short lived.

[Mike G.]

Re: Suction Throttle Valve vac source?

Dan: the 1965 shop manual supplement has a 50 page section on A/C, including the tests you're interested in.

The vacuum line to the regulator is, in fact, teed from the intake vacuum fitting. The other side of the tee goes thru the firewall to the vacuum switch that controls the coolant flow valve on the intake to your heater core.

STV's are pretty easy to overhaul, once you locate a piston/diaphragm assy. Instructions are included in the shop manual info mentioned above.
If you end up needing the piston/diaphragm assy--I can help you there.

Expansion valves are not generally rebuildable, to my knowledge, but they do have an inlet screen that NAPA carries replacements for. That's the most likely area for your blockage since it's before the STV.

Mike

[Dan M.]

Re: Suction Throttle Valve vac source?

Thanks for the help. I'll get a kit for the STV and flush the evap while it's apart. The receiver's rebuilt and the compressor is a remanI just put on to make it through the summer while I send mine out to get rebuilt. It has a front seal leak. Thanks again. Dan

[Jack H.]

Re: Suction Throttle Valve vac source?

Two tidbits:

(1) When you're flushing out various system components, they WERE originally filled with a certain amount of refrigeration oil. You'll want to make sure you replace that oil after you've done the flush/clean... If memory serves, the Shop Manual (Chassis Service Manual for '66 and later cars) documents the amount of oil to be used in the separate A/C components.

(2) When you send out your original A-6 compressor, the rebuilder is going to have a choice of the front shaft seal/bearing kit he uses. Originals from the era were sintered metal while the later service replacements (slightly more expensive) were ceramic. The ceramic parts, when properly installed, last MUCH longer...

Last, the nose of the compressor was factory equipped with a small absorbant cloth. This 'soaked up' stray refrigeration oil during the compressor's break-in period for the seal/bearing. Few who provide rebuilt compressors or those who do individual overhauls bother to replace this piece...

I've seen a couple of the mass re-manufactured compressors come with a note in the box telling you to EXPECT some oil leakage during the compressor's break-in period. That's not too professional in my book!

And, one more thing, when you change out a compressor, don't just turn it ON, verify operation, and put the system to 'sleep'.... Go log a few hours run time on the new compressor to get that new bearing/seal interface nicely run-in and properly seated!

[Terry M.]

Re: Suction Throttle Valve vac source?

Last, the nose of the compressor was factory equipped with a small absorbant cloth. This 'soaked up' stray refrigeration oil during the compressor's break-in period for the seal/bearing. Few who provide rebuilt compressors or those who do individual overhauls bother to replace this piece...

I've seen a couple of the mass re-manufactured compressors come with a note in the box telling you to EXPECT some oil leakage during the compressor's break-in period. That's not too professional in my book!

That "small absorbant[sic] cloth" was nothing more than a piece of felt -- maybe 1/8 or 3/16 thick, and sized to fit in the opening and wrap around the compressor shaft. I would start looking for that kind of felt at one of the hobby or fabric stores. I would bet you could get a lifetime supply for next to nothing.

[Jim T.]

Re: Suction Throttle Valve vac source?

Thanks for the help. I'll get a kit for the STV and flush the evap while it's apart. The receiver's rebuilt and the compressor is a remanI just put on to make it through the summer while I send mine out to get rebuilt. It has a front seal leak. Thanks again. Dan

Dan the previous post by Mike Geary and the mechanic you mentioned gave you some very good information about the stinless steel cone screen that is in the inlet of the expansion valve. If this screen is full of debris, the air conditioning system is not going to function properly because the R12 cannot flow through the expansion valve properly. This should be your first check before your purchase for rebuilding the STV valve.
The stainless steel cone screen can be cleaned and reused.