What a difference a replaced AC expansion valves does

[Sunroof]

I had my 1973.5T in the shop recently to check out the air conditioning system. This was a dealer installed (Behr) unit back in 1973! About 8 years ago I replaced the hoses and updated the York compressor with a Denso.

Of course the darn thing was blowing warm air as i t always has and although I did remove and clean the front and rear condensers and added a new drier before recharging nothing changed! My mechanic said, "look, before even considering the compressor as the problem, let's remove the evaporator and change out the "expansion valve".

Interesting that once the evaporator and fan was removed from the smugglers box a few sockets, nuts and even a small wrench was discovered. Treasures left over the years! The evaporator was pretty clean given that a cabin filter does not exist.

So the expansion valve was replaced and AC system (almost 2 pounds) charged up. With fingers crossed, I started it up, turned on the fan switch and low and behold the damn thing blew COLD!!!!!

We are very hot down here in the south right now, but I discovered even in 90+ heat the AC system was sufficient enough to dehumidify and cool off the cabin. It does not freeze you out but, good bye sweaty rides on vinyl seats for now.

Lesson passed on? Try replacing the expansion valve first (cheap).

Bob
1973.5T

[Mixed76]

Great post, thanks!

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[bazar01]

Good fix.

A gauge manifold should be able to diagnose a bad compressor or an expansion valve that is not opening to let refrigerant flow to the evaporator.

[Sunroof]

I guess the expansion valve clogs up after so many years and the fix is far less than a new compressor. Anyways, when they removed the evaporator I finally found my lost 10mm socket!!

[kuehl]

Originally Posted by Sunroof

About 8 years ago I replaced the hoses and updated the York compressor with a Denso.

Of course the darn thing was blowing warm air as i t always has and although I did remove and clean the front and rear condensers and added a new drier before recharging nothing changed!

Interesting post Bob. And great to hear you have working AC.

Maybe you did have a problem expansion valve (TEV for less typing; or TXV or whatever floats the boat).

But, I'd have to say that if every 911 or 930, say from 1966 to 1989 with factory ac, that was not blowing cold had its TEV replaced and blew cold ac, AND the conclusion was the TEV was the issue, well, that would be interesting.

Normally you can diagnose an issue "at" the TEV.
Closed or blocked valve = low low side pressure.
Open valve = normal high side pressure but higher low side pressure.

However, those 2 simple statements above are not enough to convict the valve to retirement.

A "closed or blocked valve" means the evaporator core is starving for refrigerant, running too 'lean': the diaphragm or circuit in the valve that throttles the valve needle to its seat is not working normally. This could be a mechanical failure in the valve mechanism or it could be debris. Debris could be blockage before the valve inlet (ice, drier desiccant, "oil snot" which is old congealed mineral oil, old ac hose particles or other foreign matter). Ice or moisture can develop before the entrance to valve or inside the valve .... even if you have replaced the drier and pulled a vacuum. "Pulled a vacuum" means although you connected a manifold gauge set and needle on the low side gauge says you are near 30" inHg but what has happened is all the moisture never left the system, it froze inside (yup it happens; you can turn that liquid or gaseous H2O into a solid (freeze) before it has timed to vapor out). This is why on long refrigerant runs (lots of hose) you flush out the ambient gases (air) using nitrogen or refrigerant. Many times these systems are evacuated and charged and the first time results are not good. However after repeated refrigerant recovery, evacuation and charging the "TEV issues" disappear.

An "open valve" means the evaporator core is engulfed with refrigerant, running too 'rich'. Again it could be a mechanical failure or debris in the valve and seat. And, many times repeated repeated refrigerant recovery, evacuation and charging the "TEV issues" disappear as well.


All of this is not to say you did or did not have a failed TEV. Simply, its better to diagnose the issues than throw parts at the problem.

Enjoy your cool summer ride.

[Sunroof]

Thanks Kuehl.........
Your the experts and great insight into the system. Perhaps I was lucky that the "TEV" was all that I needed to correct. Granted, the air is not that cold to warrant wearing a sweatshirt, but cool enough to stop the sweat factor and arrive more comfortable. That's amazing in itself for a longhood AC system.

Bob

[gsxrken]

Bob glad you’re up and running.
Charlie- thanks for the detail. What would you suggest for future searchers in a similar situation? Where do you stand on “AC flushes” as an ingredient in returning a long dormant system to service? Thanks

[Nick Triesch]

A few years ago I also replaced my expansion valve because the unit was just blowing warm air. It worked in my 85 Carrera!! It was a very cheap part and easy to replace. Still blowing semi cold to this day!!!!!!! My cat has larger AC vents than my Carrera!

[kuehl]

Originally Posted by gsxrken

Charlie- thanks for the detail. What would you suggest for future searchers in a similar situation?

The purpose of my post is to advise anyone searching the topic key word in the thread title is to be aware that they should diagnose the issue before they toss parts at the problem.

Originally Posted by gsxrken

Where do you stand on “AC flushes” as an ingredient in returning a long dormant system to service? Thanks

I'd suggest another thread on the topic. But briefly, flushing does not return a system, its a procedure used as an attempt to clean hoses, condensers and evaporators (with TEV removed). And, it will take you nearly 6-8 hours to do it correctly. Flushing does not 'guarantee' you will clean the components nor does it guarantee it will return the system back to factory performance ..... which was not good to begin with for most people.

[ganun]

Check out the thread " AC repair after 8 years" by ganun. Lots of pictures. Barely cool air from blocked valve.

[Nick Triesch]

Kuehl , you are correct. It’s just that the expansion valve is so cheap and easy to change out.