When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I had replace the heater control valve recently because the old one was leaking. Now I am getting no heat at all. The valve I put on is a Four Seasons 74602. Pretty sure it's the correct part. Any suggestions on why this would not be working or how to troubleshoot? It worked fine prior to replacing this part.
I had replace the heater control valve recently because the old one was leaking. Now I am getting no heat at all. The valve I put on is a Four Seasons 74602. Pretty sure it's the correct part. Any suggestions on why this would not be working or how to troubleshoot? It worked fine prior to replacing this part.
Here's a hint. When the applications show the same valve for a 1971-72 Cutlass AND a 1971-1979 full size, you know that ONE of those listings is wrong. In this case, 74602 is shown as fitting pretty much all full size GMs from 1971-1985, which means that it is a normally open valve that closes when vacuum is applied. All A-body cars through the 1972 model year use a heater valve that is normally closed and opens when vacuum is applied. As with Olds motor mounts, most Olds heater valve catalog listings get this wrong.
Here's an easy test. Disconnect the vacuum line to the heater valve and plug it. Now see if you get heat. If you do, that's the wrong valve.
It's easy to check the vacuum operation to the heater valve - just pull the vacuum hose off the valve and see if it gets vacuum with the temp slider on WARM or COOL.
Apparently mine operates opposite of what the literature says, but I have a valve that matches the vacuum operation.
From another discussion about heater control valves back in 2017:
I have the same valve on the shelf for my car.
It is stamped with:
TYPE H25
RANCO
COLO, USA
The backside has an ink label:
H25-124
The valve is normally open and takes vacuum to close.
Just today I was working on the car, changing the heater core and I'll install the new heater valve tomorrow. I connected a vacuum gauge to the heater valve vacuum hose on my car and it has no vacuum with the temp slider on WARM and vacuum with the temp slider on COOL, so this valve matches my car's vacuum operation.
I recommend you check the vacuum operation on your '72 to ensure it matches your heater valve as my '71 operates opposite of what the factory manual describes per Joe's posts.
Last edited by Fun71; October 30th, 2018 at 12:05 PM.
Way back when the Four Seasons brand valves were good, but in the link I posted above Joe said he has had issues withe the Four Seasons and AC Delco valves that are/were made in Mexico. I got lucky and found one that was made in USA.
Not sure about the quality of any parts these days.
I am a lot of trouble finding the correct heater control valve for my car. So far I have purchased 2 of the p/n 411822 valves and both have been normally open type valves. The sellers on Ebay accepted returns on both, so I'm only out the shipping on one of the valves, the other was free shipping. The parts stores around me show the Four Seasons valve, but the one they call out for my car is normally open, which is incorrect.
Can someone please tell me where I can purchase the correct valve for my 71 442 from a reputable seller? I would prefer a valve similar to the one in the following picture, but any normally closed valve that will fit is acceptable. The picture shows a Buick valve so not sure if that will fit my car. The threads in my intake are 3/4" NPT.
Didja try Rock Auto or NAPA or a higher end privately owned parts house(read not big box)? What about Fusick Year One etc...?
To keep these valves in good shape you need to actuate them regularly and keep the coolant fresh, read not acidic. PH test strips will help you know when its losing PH.
Every time I get into my car I make sure to actuate the heater hot/cold lever. I move it several times from cold to hot..
Im having a problem for the last 15 years where the replacement valves cause a strange harmonic resonant sound when the temp control is moved to hot and engine RPM are above 1700. The orifices (coolant passage) hole ID is smaller on the repro valves. Have narrowed it down to this as a possible cause. The car is nearly un-drive able with the heat on with that noise!
I have looked high and low. All valves I have found are normally open, when I need normally closed. The ones listed on RockAuto and big box stores here in town cross reference to the same normally open valve. The privately owned stores, the same.
On the noise you are experiencing, do you think the valve is just not opening up all the way?
"On the noise you are experiencing, do you think the valve is just not opening up all the way?"
Dam good thought. Next time I go at it Ill give it a test. I drilled the ID to its max on a valve exactly like the new valve seen here(I purchased 2 at the time). It's still smaller than the OEM. I was thinking of trying to go the opposite direction to restrict it down with a threaded insert.
(Note the drilled out valve is not shown, But that tapper you see was almost completely removed in the unit I modified which is currently on the car. Still have the noise though it was slightly decreased so I think I was on the right path)
74601 is the 4 seasons number I have.
The new valve on the left is the 74601.
The other on the right may or may not be the OEM?
This is for a 68 400 with A/C...obviously.
Last edited by droldsmorland; December 11th, 2018 at 06:25 PM.
Thank you droldsmorland!! I will try to get the 4 seasons number you posted. Let me know if and what you did to get rid of the noise. Hopefully I don't get the noise with the new valve.
Just got off the phone with the local parts store. The 4 Seasons 74601 is 1/2" NPT, the valve I need is 3/4" NPT. Would you have a p/n for the normally closed valve with 3/4" NPT? Otherwise I would need to use a reducing bushing.
John, I thought I had an extra but didn't. This is normally closed and has to have vacuum
to open. It is the small 3/4 NPT. You may search the # on it. Kinda stupid, it reads one way, flip it over, it reads another.
Thanks Tru-blue, but neither one of those numbers are valid Four Season p/ns. The p/n I am seeing for four seasons start with 746xx. 74601 is 1/2" NPT normally closed and 74602 is 3/4" normally open. I called Four Seasons and they said they do not make the valve I need. Can anyone provide a p/n for a valve that will work for me? 3/4" NPT, 5/8" hose vacuum to open (i.e. normally closed) is what I need.
Are you certain that your intake manifold is the correct year for your car? I thought the change in vacuum operation coincided with the change in thread size. Ya know, to keep folks from installing the wrong valve. Seems as if I remember my '70 Supreme had a different size valve than the '71 Supreme, but it's been 30 years or so and my memory may be off. If anyone knows for sure one way or the other, please post up and let me know.
Note in the images below that the heater valve port is much larger on the 1971 and 1972 intake manifolds than it is on the 1970 manifold (images taken from Chris Witt's excellent archive contained in https://classicoldsmobile.com/forums...-thread-3.html)
FYI on the heater core noise, years ago I didn't use a heater valve and the unrestricted water flow resulted in a loud "water rushing" noise in the core. After installing a heater valve that has a restriction, the noise went away.
Last edited by Fun71; December 12th, 2018 at 08:59 AM.
I do see it listed as either NPT size on a couple of sites. Thats a new on on me. Of course the link I embedded for Advanced says the sites down for maintenance.
Are you sure your measuring correctly? NPT is different from tube and bolt thread. For example, a 3/4"NPT pipe thread has an outside diameter of 1.050 inches. Worst case is you need a bushing to make it work to get it on the road. Have you Googled 74601?
Correction I think the couple of sites I thought had 1/2 and 5/8 NPT thread sizes was actually the 5/8 hose size. They just didnt spoon feed me. 5/8 NPT is rather Odd. Its usually 1/2 and then 3/4.
@Kenneth - Yes my car is a 71 so yes opposite from the 70.
@droldsmorland - The link you posted did not take me to a part. Yes I am sure of the pipe size. I am an electrical contractor and deal with pipe sizes all the time. I actually called 4 Seasons. They said they do not make the valve I need and that the 74601 is 1/2" NPT.
Can't believe it's this difficult to find the correct valve.
So you're saying the heater valve control on your '71 is the opposite of my '71? Mine has no vacuum with the temp slider on WARM and vacuum with the temp slider on COOL.
This means my car uses the readily available normally open heater valve that you keep finding.
Last edited by Fun71; December 12th, 2018 at 11:05 AM.
Are you sure about that? The valve on the car right now is normally open with no vacuum. I removed the vacuum line from the valve and I get heat and plenty of it. When I attach the vacuum line and put the selectors to heat and warm I get no heat.
Am I sure about what?
If you mean the vacuum operation of my car, then yes, I am certain of that as I checked it with a vacuum gauge as described in post #3 above.
So I may or may not have found the reason why people have so much trouble getting the correct valve. Seems GM has superseded GM p/n 411822 which is normally closed with GM p/n 411823 which is normally open. There's the rub.
So I'm back to the same question. Where am I going to get the correct valve for my car?
Not sure why your car is like that. To quote Joe from above and he also states this in the thread you posted a link for above as well:
"Here's a hint. When the applications show the same valve for a 1971-72 Cutlass AND a 1971-1979 full size, you know that ONE of those listings is wrong. In this case, 74602 is shown as fitting pretty much all full size GMs from 1971-1985, which means that it is a normally open valve that closes when vacuum is applied. All A-body cars through the 1972 model year use a heater valve that isnormally closed and opens when vacuum is applied. As with Olds motor mounts, most Olds heater valve catalog listings get this wrong. "
I must have got lucky on the motor mounts, cause they match the ones that came attached to the motor.
Yeah, a while back Joe even posted the page of the CSM with that info. I can't say why my car doesn't match that, but I'm glad of what it is as I didn't have the issues you are experiencing when replacing the heater control valve. The parts I have all work together to give the correct end result - heat with WARM selected and no heat with COOL selected.
Humm...couple more Ideas...Ill go the Shainin route...lets peel the onion. Whats changed....Just the part? Bad part(s) out of the box? Mis-marked part? Not dealing with OEM parts?
1. Is the intake a OEM 71 W intake?
2. Was factory AC possibly added during a restoration?
3. Try calling the Fusick or Year One vendors. Keep in mind other GM brands may use the same/similar valve. Look at Chevy, Pontiac, Buick even Cadi and Vettes. The latter two wont have the valve. Just for future ref for other commonly shared parts such as high quality points/condenser sets...think NCRS and Vettes, those guys are nuts...Im one of them.
4. Contact https://www.classicautoair.com/ and https://www.vintageautoairconditioning.com/ These guys may have some answers.
5. You're an OCA member, have you put out an APB on the wire there?
6. I know the 74601 fits 68-70. I have installed it on 68-70 in the past with OEM Intakes. Joe said including the 72 model year. Thats a well known fact.
7. I see all 4 of the part numbers mentioned in this thread "available" when inserted into the Googler. Availability may be another story. Glad I bought two when I did about 8 years ago.
8 Could the intake have been altered? I have seen at least one case where this coolant port was redrilled up a size to correct a severe cross thread. Mechanic tried a Helicoil but it wouldn't stop leaking. Yes a bushing was needed. Today that could be repaired correctly for sure. Nobody knew what theses intakes meant in 78.
9 How about some pics of your intake and both of the valves.(you did say you returned parts so this is moot).
10. Did you verify the vacuum signal at the connection point to the valve while actuating the dash temp control, car running? What does it do? On Hot should have full vacuum? Chances are in the last 48 or so years someone else has been in there. You may need to start with the controls and work out to the valve as a systematic approach of eliminating variables.IG,,, Cable adjustment, blend door working etc...Maybe someone before you flip-flopped something not knowing they had the incorrect part for the application?
11 Does the old valve work with vacuum? It just leaks right? And is it N.C or N.O..? You can look down the throat to verity both visually.
Sometimes it helps to start over again with troubleshooting. I call it tunnel vision removal. Same as getting a second opinion. Someone else preferably a subject matter expert(SME) can come in without the blinders on and go directly at the root cause.
We're missing something here...
1) This is on my black car with A/C, so no W intake, but it is 71 original equipment intake for the 442..
2) This car was original A/C car, not added after it came out of the factory. I have owned the car the first time since 1989 and it was untouched at that time.
3) I'll try Fusick.and/or Year one.
4) If I don't get results from #3 I'll try those guys.
5) I have not thought about OCA, good point! Thank you!
6) The 74601 valve is 1/2" NPT normally closed, so it will work but would need to use a reducing bushing to get to 3/4" NPT. I have one on order at the local parts store as last resort.
7) I have purchased GM p/n's 411822 & 411823, they were both the same valve. 3/4" normally open. So I'm guessing one was in the wrong box. Have not seen any others available.
8) No way, this car was untouched when I bought it. It was quite the find. Triple black bucket seats, plus other options. Original W25 with the spoiler. Nothing has been altered. I'm positive.
9) I can get pictures of the intake and one valve when i get home tonight. Will post later.
10) I have tested vacuum, yes vacuum when on heat. I was just under the dash getting the duct work back together. I triple checked the vacuum hoses to the heater control cause I had to remove a couple hoses to reroute wires, etc. I triple checked it with my chassis service manual. All good there.
11) Yes the old valve worked fine just leaked. You cannot look down the tube to check because it's offset. I may still have the old valve in the garage i will look, but everything worked properly prior to installing the valve. Did not verify normally open or closed, but all I did was change the valve and now it does give heat with the vacuum disconnected.
My thoughts are I just have not found the correct valve yet, but I will check everything again to be safe. Will let you know what i find.
Last edited by friesjh; December 13th, 2018 at 04:27 PM.
Well I got some pictures, apologies I didn't get better pictures. So the casting is 407567 and the date looks right, but from what I can tell this a casting for a MT car. But from looking at the parts manual it shows a different intake for OAI cars. Problem is the parts manual I have does not list the part number for the OAI intake. The person who rebuilt the engine said he thought the motor had never been apart. So now I don't know what to think. Why would it have the MT intake on it if was original to the engine? See pictures attached.
No Pics John. You have to use a resizing tool or this site wont load, They just go off into cyber space.
Some genius geek decided to change the process recently, now you need to resize (more gymnastics just what us old guys need) .
Jaunty posted a link to a good one for microjunk...look for the tag "posting pictures" or similar in the search here.
October 30th, 2018, 10:40 AM
