Heater Control Valve
5 / 2012 R. Kwas, changes on-going
Function of the Thermal feedback
Influence of the Thermal Sensing
Disassembly of the HCV
HCV Failure modes
Further Tucker Information
Reference 1: Ranco HCV Rebuilding instructions.
Reference 2: Ranco Rebuild Kit (NAPA/Balkamp BK660-1000).
FIGURE 1. Extract from Volvo Parts Catalogue.
An ever increasing number of owners are experiencing failures of their Heater Control Valve (HCV). It would seem that this is mostly due to the age of the rubber, so replacing with a used valve is clearly not a good option, as the replacement will likely be as old, and I wanted to have a good understanding of the assembly before exercising the expensive option of replacing a valve with new, with a lofty price. This article is intended to understand the construction of the valve, and its failure mode(s). After having taken apart an old, used valve, which was graciously made available for me by Chris H. (a.k.a. Agent Strangelove) and the STrangelove Reverse Engineering and Pastry DevelOpment Kitchen (STREPDOK, et. al.) with the intent of evaluating the design, and investigating the potential for rebuilding, including estimating the chances for success of such a rebuild, I have to say that in my considered opinion, I rather doubt if these assemblies are suitable for rebuilding by the casual mechanic, but I'm getting ahead of myself...
FIGURE 2. Side 1. Manufacturer’s name, Ranco, country of manufacture, and the number H16 are revealed
from under forty plus years of surface corrosion. Locking tabs of the housing can be seen straightened
in preparation of disassembly.
A quick search reveals that Ranco is still in business, including in the US, with a specialty of temperature control. It’s nice to see that the place is still around, although there are indications on their site that they are under attack by manufacturers of counterfeit products which are undoubtedly made cheaper than the original.
FIGURE 3. Side 2. Bowdon cable termination and interface with mechanism can be seen.
The capillary tube has been cut, and so is compromised, but Valve No1 is never intended
to see service again.
FIGURES 4A, B. Graphic of Heater Control Valve Body showing action of Seal.
Seal not only provides sealing action for housing but also return spring force to Actuator Pin.
Valve Design Considerations and Use in the Volvo Heater Core Circuit: The valve is a series, fully blocking or continuously variable flow type. It is plumbed into the B18 / 20 cooling system downstream of the Heater Core and in such a way that the coolant flow will tend to push open the valve. When at rest, that is, in the non-activated position, the Actuator Pin (AP) is such that no coolant flow is allowed. Only when the AP receives pushing force from the mechanism does it come off its seat and coolant is allowed to pass.
Function of the Thermal feedback for closed loop control: A capillary sensing tube is positioned in the Heater Core housing, in the airstream on the downstream side of the Heater Core, and in this manner senses the air temperature after it has been warmed by the Heater Core. An expansion bulb located on the other end of the capillary tube in the HCV mechanism, adds this (minimal, 25% estimated, see: Influence of the Thermal Sensing ) Thermal Sensing input into the (driver-set) Mechanical Setting, to maintain a constant temperature.
FIGURE 5. B18 / 20 Heater Core Circuit showing location of Heater Control Valve in the coolant path.
Disassembly of the HCV, the First Reason against Rebuilding: …The valve was just not intended to be rebuilt! Now this has never stopped the determined vintage vehicle rigger / I-believe-I-can-fix-anything-including-a-rainy-day mechanic (like me) from bending back a few tabs or drilling out rivets which hold a housing together, to gain access to internals and see how much restoration work I could apply (or havoc I could wreak). But the extent to which the HCV must be disassembled involves mechanical forces and insult to a level that one has to question if the mechanism would survive being subjected to these forces a third time during reassembly.
There is no such luck as simply drilling out a rivet or two to get access on this part! In order to disassemble the actuating mechanism from the plumbing assembly to gain access to the seal, thick brass locking tabs which are part of the valve body and which hold the assembly together securely must bent back with substantial force…(See Reference 1: Ranco Repair Procedure, Valve Disassembly Instruction No. 3) in my sample, this included impact force to first get under those beefy tabs, then the further application of non-precise force (read: muscling the crap out of) to persuade the tabs to straighten.
FIGURE 6. Showing Locking Tabs after straightening and what’s left of a half
century old Seal (wet side shown, exhibiting plenty of surface crazing…at least!).
When the tabs were finally bent back enough, and straight, and all aligned to allow withdrawing the plumbing assembly from the mounting plate, lots of micro-fracturing was apparent at the tab bend roots. I would certainly never attempt to bend these back over at reassembly time…they would surely be in jeopardy of breaking off completely putting the rebuild into more complication and jeopardy. Locking them back in place by soldering came immediately to mind since the brass would be solderable to the steel base…but I wonder how well the heat necessary for that would play with the rubber seal nearby…I’ll cross that bridge when I come to it…!
After finally manipulating all the tabs enough to be able to separate the two sections (no small feat!), then figuring out how to gain access to the actual seal and removing it, I found the valve section to be a precision assembly certainly worth rebuilding, but with a specialized seal of a very specific shape…a simple O-Ring or circle of rubber cut from sheet-stock will not even come close to doing the job here!
I also found the dry side of the (neoprene) seal from my sample had much less surface deterioration than the wet side…this is rather unexpected…it suggests that the coolant attacked the rubber more than the air, and I have trouble explaining that...I would have thought the dry side would suffer under more attack by ozone etc., but apparently the coolant (or just water) is also able to do a number on the seal after time. As a result of this attack, the seal was compromised to the extent that it had a noticeable through-hole, so my sample valve was certainly a “leaker”.
FIGURE 7. HCV Valve Section Disassembled (dry side of Seal, with minimal deterioration is shown).
Coolant Flow through the Valve Section is controlled by head of the Actuator Pin (AP) position as set by a combination of driver temperature Mechanical Setting (transferred from the dashboard controls by a Bowdon push/pull cable) and remote Thermal Sensing by the capillary tube sniffing the air temp at the air-box. Both inputs are combined to exercise substantial mechanical advantage over the end of the AP protruding into the mechanism. Inside the Valve Section the AP head is either against the coolant sealing face, completely blocking flow, or away from the sealing face by some variable amount, allowing continuously variable partial to full flow. It’s a closed loop temperature control system…no electricity necessary!
HCV Failure modes: If the AP head were to fail to seal well to the seat, the worst thing that would happen is the valve would allow some leakage level of flow through the heater core circuit…not optimal, especially in August, but the Heat/Defrost airflow control could still be adjusted to minimum to reject the heated air and minimize warming of the passenger compartment…so it would be uncomfortable, but not the end of the world…but an inability to stop cabin heating when Temp Control is set to Cold suggests it is time to check the wire control linkages to assure the HCV mechanism is being set to the closed position by the setting of the control (the common cause of this is a binding Bowden cable (it should be lubed and exhibit low resistance to movement), OR a slipped cable sheath at either end (problem is as covered under choke cable article…recommended correction is also shown there LINK: Check your Choke), OR possibly the internal AP sealing is indeed no longer working as it should…checking this would require an involved and difficult test or disassembly of the HCV.
The Seal which
would allow leakage of coolant from the valve body is the Assembly and
Actuator Pin Seal. First, its flat perimeter seals between valve body and
base plate. It is in compression between the two. This is pretty easy
duty…there is plenty of material cross-sectionally to do the sealing, and when
in place, both sides are protected from ozone and UV attack to a great extent,
so are likely to last a long time.
The second part is much tougher! The center area is snapped over a groove in the AP and further sealed to its shaft by a circular spring-ring (on the dry side). It is held in place by a small cup and retaining spring. In the course of moving the AP through its operating range to control coolant flow through the valve (a mere 1/4”of travel), the center part of seal, being locked to the pin moves along with the pin (it does not need to seal against movement along the pin), but it is exercised similar to a speaker diaphragm…held fast at the edge, moving along an axis in the center…(or better yet, a cuica see: http://en.wikipedia.org/wiki/Cu%C3%ADca ).
The neutral position of the AP (that is, when the Seal is not preloaded in either direction) and seal assembly is such that the coolant seat is closed.
Another Reason for not Rebuilding the HCV: Availability of seal…apparently these seals are difficult to get…although I have the NAPA number (Reference 2: BK660-1000), I have been unsuccessfully trying to get a “Rebuild Kit” or simply a replacement seal for 6 months now!
…but for owners out there with coolant puddles on the passenger floor, there is hope beyond simply short circuiting the entire Heater Core loop to prevent the pesky leakage onto the passenger floor (and not having an option for heat because there is no coolant flow through the core)…or alternately, short circuiting the HCV allowing continuous flow through the Heater Core (and not having the ability to turn OFF the heat)!
* One Jim Tucker in
www.heatercontrolvalve.com ) apparently has developed techniques to rebuild
Ranco HCVs as used on our vintage Volvos, as these were also used on
American vehicles of the same era. I
contacted Mr. Tucker, who told me that he has some twenty years of experience
rebuilding HCVs…he was also friendly, knowledgeable and very forthcoming with information
(See also: Further Tucker Information…below!),
and he advised that he does not stock the Volvo valve…I would have to send him a
core to rework.
I have yet to get an example of his work into my hands for evaluation, so I can give no impression of the work and/or value yet. This is planned. Any readers and customers of his are also welcome to send their impressions of dealing with him and his work. If Mr. Tucker has developed techniques and special fixturing with which to turn out quality rebuilt HCVs, I may not need to!
UPDATE: OCT 2012 My Tucker Experience:
Since I could not acquire a rebuild kit (NLA?), I even gave an “insider”, employed by one of the national parts chains, a chance to supply me with one (Thanks for your efforts John A.!), I thought I’d give Mr. Tucker a chance to impress. A second, used HCV (Valve No. 2) was procured from Agent Strangelove for the purpose of letting Mr. Tucker work his Kung-Fu on it. This was a slightly different (later) model as the earlier one shown above, this one marked with an H only. It also exhibited a lot less corrosion…I contacted Mr. Tucker again, advised him I had a core valve from a vintage Volvo, and requested he work his magic on it (and to also include a second rebuild kit for me to study and show here). He quoted me $130 for everything, including shipping…off Valve No. 2 went to him…
Before Pictures of the Valve No. 2: (Pretty much as received from Agent Strangelove.)
FIGURE 8. Valve No. 2. Parts that aren't copper or brass are zinc-chromate plated.
FIGURE 10. The valve was in decent shape, and came complete with the remains of an arachnid summer residence!
After Receiving the Rebuilt Valve Back: About a week after sending it off to Mr. Tucker, Valve No. 2 came back per USParcel Priority Post. It was protectively packed, and included the additional seal kit I had requested. He had rebuilt the assembly as arranged, and as part of his service, bead-blasted the components, so it looked quite nice, with not a speck of rust or corrosion (or the yellow, anti-corrosive zinc-chromate plating) in sight. The mechanism was lubricated so it worked smoothly and with a minimum of counter-resistance.
The locking tabs which caused me great concern were bent back in place, less than originally, to hold the assembly together, but seemingly perfectly adequately to perform their function…and maybe that’s the key...they don’t have to be bent over fully, like they were originally at the factory…and since they don’t need to endure another full bend, a partial bend being enough to secure the assembly but not enough to cause breakage. (See also: Further Tucker Information…below!) The general impression was: Pretty Nice, but being a long-term satisfaction required type of guy, I’ll coat it with a clear lacquer to keep it that way!
After Pictures of the Valve No. 2:
FIGURE 13. Post-Tucker Detail 1. Retaining tab at Red showing a much less than full (but adequate) bend.
Green points to dry-side of Actuator Pin Seal and target for a generous protective blob of silicon grease.
FIGURE 14. Post-Tucker Detail 2. A Torx(!?!) screw used to adjust the action of the capillary tube feedback is visible.
Presence of the Torx screw (which according to a popular on-line reference, was developed in '67), confirms that
Agent Strangelove sent me a fairly new Valve No. 2. .
Leak-Down Test: A thorough evaluation of the rebuild requires a bit more than just an inspection, and being impressed by a bead-blasted clean assembly. A functional test is in order.
Highest operating pressure of the cooling system that I have seen specified for the various cooling systems is XXXXPSIG (this pressure is controlled by the Radiator/Overflow-Bottle cap). After plumbing up the valve to a Stant cooling system pressure tester, 2X was applied pressure and this pressure was left one hour before checking the gauge for a drop.
Pic of Leak-down Test Setup: PLACEHOLDER
Leak-down Test Results: PLACEHOLDER
General Impressions/ Conclusion:
All in all, I’d say Valve No. 2 was nicely rebuilt by Mr. Tucker and it certainly looks ready for another half-century of failure-free duty…not bad for a hundred dollars!! At this point, if you are experiencing a leaky HCV, my recommendation would be to go with his service...it just might be the best $100 you ever spent on your vintage Volvo! It should be said that this recommendation is my own impression of his service, supported by the pictures and data you see here. I haven’t even actually installed this valve into a vehicle yet! Mr. Tucker has not shown me any consideration, monetary or otherwise for this endorsement, and I make no predictions, and take no responsibility for any dealings other parties may have with him…but he did alright by me!
Further Tucker Information and Answers to Additional Questions which Mr. Tucker was kind enough to Answer:
After receipt of the reworked valve, I contacted Mr. Tucker and asked if and how he preloads the rubber seal during reassembly and while rebending the locking tabs. I also asked him what lube he applies to the mechanism. Further, I asked him if he applies anything to the seal dry-side (I’m thinking that this would be a great place for a protective blob of silicon grease)… Also, since the zinc-chromate plating has been removed by the bead-blasting operation, protecting it with clear lacquer would be in order.
Question 1 - What kind of grease does he use to lube the mechanism? Answer – White Lithium grease, like originally from the factory.
Question 2 – What would he think of additional protection on the assembly seal dry side against ozone attack? Answer – He has never been asked before, and recommended against a petroleum based grease as it would not be compatible with the neoprene seal, but agreed that using silicon grease would afford long-term protection to the rubber.
Question 3 – Does he preload/compress the assembly seal during reassembly? Answer – Yes, he has fixturing which applies 30lbs. (his estimate) when recrimping the locking tabs, and in all his years of experience and thousands of valves which he has reworked, he only bends the tabs over 60degrees to secure the assembly. This is perfectly adequate to lock the assembly, and doesn’t result in tab breakage.
Question 4 – Are there different assembly seals? (I asked this because of the apparent differences between used seal on Valve No. 1 and new seal.) Answer – The seals are the same from ’41 to ’70 for Ranco [also Harrison(?)] valves(!), so any apparent bellows shape the seal took on must have been caused by the rubber taking a set while confined and under heat and pressure in the installation. (Wow…there’s another surprise…I still have trouble believing it…and could this mean that 544 and 140 vehicles also use this same HCV…individuals who can supply confirmation or details of this are welcome to contact me!) [Plumbing connections are all different, as are Volvo part numbers, so the valves are all configured differently, but apparently they all use the same seals...interesting!]
FIGURE 15. Pix of seal kit, consisting of Assembly and Actuator Pin Seal and Coolant Seat Seal (both of Neoprene):
Points of information from another phone (Nov 2016) call with Mr. Tucker.
In response to an e-mail question "...and how much is the influence of the thermal sensing on the overall result? could the "on-off behavior" of the HCV be dependent on the thermal sensing failure only?"
Regarding Influence of Thermal Sensing...if you have
the HCV removed from vehicle, you could place the Thermal Sensing tube
alternately in a bath of warm or cold water, and see how much action this
results in at the Actuating Pin, compared to the action of the Mechanical
Setting. I would be interested in your findings and would add them to the
article. I did not actually perform such a test for my article, so I estimated
the amount of influence of the Thermal Sensing, after inspection of the
mechanism and may have understated it...it may indeed be able to fully control
the valve On-Off. I will call Mr. Tucker in California and ask him for his
I just got off the phone with Mr Tucker, who confirmed that the amount of influence of the Thermal Sensing mechanism is only about 25% while the Mechanical Setting is in mid-range, and zero while valve is fully open or closed, so my estimate was realistic, but now that I have a number, I will add this to the article. He also confirmed that flow into the Valve is in a direction which will tend to open valve to allow flow as I already mention in the article.
Additional Pix from Mr. Tucker’s site:
FIGURE 16. Pic of 49-50 Hudson HCV from Mr. Tucker’s site…looks pretty familiar!
Pic Source: www.heatercontrolvalve.com
FIGURE 17. A exploded Pic of a similar HCV with Valvebody removed from baseplate. Folding tab assembly locking system is used here also. Both seals are shown. The small seal located on the Actuator Pin, which seals against the seat to stop coolant flow, is shown removed from the pin, and the larger main assembly seal. Pic Source: www.heatercontrolvalve.com
For individuals needing to cure leakage, but not quite prepared to support the efforts of Mr. Tucker, I present a cheaper, more “rustic” solution here. It consists of a common 1/2” ball valve and associated standard copper tubing replacing the original valve and mechanism, such that a manual control of Coolant flow through the Heater Core circuit can be exercised …there is no thermal feedback, so the flow will need to be controlled by reaching under the dashboard to actuate the valve lever, but I’m thinking that the temperature could be adjusted by varying the airflow, minimizing the need to reach under the dash…and don’t talk to me about “distracted driving”…
I made this assembly, reminiscent of something used by brewers of ‘shine in the back-woods of Kentucky, with parts entirely purchased at my local plumbing supply place, for the total parts cost of around $XX.
Configuration of the HCV fitted to 1800 models is a bit different from the one fitted to the 122...whereas both hoses depart the plumbing part straight, on the 1800 valve, they depart at right angles to clear the hood: http://www.volvoforums.org.uk/showthread.php?t=262880
The valve used on some SAABs looks very familiar(!): http://www.saab-v4.co.uk/speedball/topic.asp?topic_id=920&whichpage=1&SearchTerms=heater,valve,repair
Reference 1: Ranco Repair Procedure [Thanks Chris H.! ]:
Indeed, it looks like they supplied OEM valves for a number of Volvo models (although they transposed two highlighted digits on the 544 part number).
Reference 2: Ranco Rebuild Kit (Balkamp number BK660-1000):
External material attributed. This article is Copyright © 2012-2016. The terms Volvo, Ranco, and Stant are used for reference only. I have no affiliation with any of these companies other than to present my experience, and highly opinionated results of the use and care of their products here. The information presented is my own, and can be used or not, or ridiculed and laughed at, at the readers discretion. As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles!
You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source. If you don’t, you’re just a lazy, scum sucking plagiarist…so the Boston Globe wants you! As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and maybe wise-a** comment.