1966 Heater Control Valve Issue! Discouraged!

[gofast123]

Well, just as I feared...  I finally decided to get my A/C working again and plowed quite a bit on money into parts and labor.  Unfortunately my mechanic just called and told me that the heater control valve doesn't appear to be functioning properly.  When the A/C is on, it's not switching off flow to the heater core and as such I'm getting warm air mixing with my cold air.  Other than the obvious (a bad heater control valve) and suggestions on what the culprit might be here?  He mentioned it could be vacuum issues.  If it is a bad heater control valve, are they readily available?

[35-709]

Heater control valves should be readily available at NAPA, etc.  Rock Auto has them listed for your '66 at less than $20, they were used for years.  l

[chrisntam]

If the new HCV doesn't fix it, give Cadillac Tim a call.  I also highly suggest you buy a copy of his a/c manual for your year car.  I bought one for my '70 and its fascinating reading!

http://cadillactim.com/page1.html

[Scot Minesinger]

The first thing you should do is buy Tim's book even if you do not use it, your mechanic could.

The 1966 heater control valve from NAPA will not have the vacuum switch that waits until car is warmed up to allow the control system to operate when in heat mode.  No matter, just pipe that straight thru with a coupling and then heat will start when you immediately start the car and there will be no delay.

The heater valve can easily be tested by removing it and out of car with no vacuum it should be open or (open I think) closed.  The apply vacuum and it should hold vacuum.  If it holds vacuum, then it should close or (close I think) open.  Then you know it is good.  If not replace it.  If it appears original due to the 48 year old rubber diaphragm I would replace it even if it tests good.  Next go the vacuum line that connects to heater valve.  Put a gauge on it.  make car go into heat and a/c, you should see the gauge fluctuate, if not you have a vacuum control issue. 

If you have Tim's book, this is where it takes over on the control issue.  Goes without saying all vacuum lines should be in great shape or replaced.  USA parts sells the color coded vacuum hoses so it looks factory.  If the lines are good, your transducer, servo, dash unit, or a combination of them could require a re-build.

Good news is the 65 thru 68 Cadillac climate controls are the easiest to work on.

[Jon S]

If the 1966 has the same system my 1983 Lincoln has (GM Harrison), then there is an external vacuum ported sensor that provides vacuum to the heater valve once the engine reaches a certain operating temperature (Automatic Climate Control).  When the AC is on, the system cuts vacuum off and the heater control valve closes.  These valves are well made and my original one works just fine.  Make sure your mechanic understands how Climate control Systems work before he just starts replacing parts.  Does your heater come on once the car has run like 2 - 3 blocks automatically?

["Cadillac Kid" Greg Surfas 15364]

With your "Automatic Climatic Control" system introduced in 1964 by Cadillac, the system produces both warm and cooled/dehumidified air and mixes them (temperature control door) to deliver air to the cabin that is tempered to provide the results the driver desires as determined by the setting on the temperature control dial.
The heater water control valve, if functioning correctly only shuts off when it receives a vacuum signal from the programmer indication the car is calling for "heavy" or Maximum cooling.
There was another function of the early heater valves and that as Scott says is to close off the control vacuum cirdcuit to the master switch until the water in the cooling system has warmed up.  This is more often than not bypassed by coupling the two vacuum lines intended to go to the valve together, thus eliminating the "warm-up" feature.
There are many books and instruction pamphlets out there, but FWIW I think the factory service manual (available in reproduction) can't be beat.
All the components , their function and operation and the electrical and vacuum circuits are all shown and explained.  This manual was intended to let the Cadillac service mechanics learn and understand these (for their day) complex AC systems.
Greg Surfas

[Commodore]

The part number for the heater control valve is Four Seasons # 74604.

[cadillactim]

It doesn't sound like your heater valve is the main problem.  As Greg said, the heater valve only shuts off water flow in full a/c mode (recirculate).

You could have more than one issue causing the temperature problem.  If you have the special tools that the shop manual calls for to test the system, you can use the factory shop manual. But I do have an easier to use manual that is very popular (have sold nearly 500 of them).  You don't need the hard to acquire special tools that the factory manual calls for, since the manual was developed knowing that 99% of us don't have those specialty tools.

Wish I could give you a definite answer of what your problem is, but there are several things that can affect not being able to control the temperature.  The manual I have addresses real world problems that come after many years of use.  The factory manual can't cover those problems, since they didn't exist when the factory manual was written.  In 1966, the Climate Control systems were only in their third year.

Tim

[Eldo66]

Well, just as I feared...  I finally decided to get my A/C working again and plowed quite a bit on money into parts and labor.  Unfortunately my mechanic just called and told me that the heater control valve doesn't appear to be functioning properly.  When the A/C is on, it's not switching off flow to the heater core and as such I'm getting warm air mixing with my cold air.  Other than the obvious (a bad heater control valve) and suggestions on what the culprit might be here?  He mentioned it could be vacuum issues.  If it is a bad heater control valve, are they readily available?

FWIW, I disconnect the heater core during the brutal Texas summer months by rerouting the heater hoses back to the radiator.  That ensures that the air conditioner's effort is not reduced by potential air mixture control problems in the climate control system.  If you're not prepared to divert the coolant flow, then you will need to check for vacuum input to the heater flow valve when you switch the system to max cooling.  It's either a vacuum input issue, or a failure of the heater valve to respond appropriately to the vacuum control input, or both.

Regards, P Nesbitt

[tudor_47]

  USA parts sells the color coded vacuum hoses so it looks factory. 

interested in the colorcoded hoses...
links to them?

[48-62]

I would fully endorse the buying of Cadillactim's book.  My garage had never worked on a 66 Cadillac before, bought the book and some parts from Tim, and they have been through the whole system and it works perfectly, live in the UK by the way, and it has been referred to countless times.
Steve

[chrisntam]

interested in the colorcoded hoses...
links to them?

Didn't see them in the catalog, gave them a call.  Spoke with Larry @ 1-800-872-2013.  They have a kit, sells for $30.  Has 6 different colored hoses 5 feet each, I think.  I ordered one.  The part # is 9.281L. 

http://www.usapartssupply.com/cadillac.php

[txturbo]

I think I would be looking for another mechanic. All he has to do is pinch off the heater hose to verify. Then just bypass it until you get the control valve problem solved either by replacement or cleaning.

[Will68]

Cape Cod located '68 convertible.

The "warm up" bypass option very revealing.    My '68 climate control worked well except when I pushed temperature dial above 79 degrees - unit would shut-off completely.   I run car with low thermostat ...I think 150 or lower (dashboard temperature indicator hovers below 1/4 position on an 80 degree day).   I rebuilt power servo which consistently gets vacuum and correctly pulls open the heater door when temperature dial is raised past 80, but fan would cut out.    I bypassed (by connecting together) the water heater valve - two side vacuum lines and now the climate control stays on above 79 degrees irregardless of engine temperature - great for quick rides to the beach.

[35-709]

"I run car with low thermostat ...I think 150 or lower (dashboard temperature indicator hovers below 1/4 position on an 80 degree day)."

The rest of your post aside, if you are indeed running a 150 or lower(?) thermostat in your 472, you not only have the wrong design thermostat in it but you are running the engine far too cold.  Those engines were designed to run hot --- 210 - 230 is common.  There are only 2 thermostats of the correct design available for your engine, one 180 and one 195 degrees.  Other lower temp. thermostats like those for a Chevrolet, etc., will fit but the design is different, not correct, and they will not properly perform the cooling function as intended in your engine.