HVAC - Packard Style

[Duckworth]

Like many I was not thrilled with the climate portion of the car, making a decision a while back to alter how temps are changed. Presenting the idea for some that may find it amusing to an extent, or worth knowing about.

As others can attest, the ability to realize the desired temp is often a challenge. Embarking on it, the number of poss vacuum leaks is alarming, but the real obstacle imo -- the presence and number of actuators built into the system.

Imo, the best climate control is the one where you adjust the temp -- without circuits, or actuators. One way to do it is allowing air to (3) places at all times, windscreen, dash, and footwell, first by removal of top actuator to windscreen and inserting a small chunk of wood to allow 30% of blower to windshield permanently..footwell and dash flowing also. Removal of actuators is a somewhat daunting task since the change is not minor, but for less than show quality car..the results are surprising.

Actuators gone, the main flap arm allowing heat to the cabin is accessed immediately. It is fairly easy to connect a rod to this arm, but somewhat harder to drill near the bottom of dash, to have a tube of the right dimension, so a rod maintains position and setting.. Obviously, it's bone simple in ways, but reaching down to pull / push a few times, it works quite well indeed. Another plus, is more room with stuff cleaned up behind the dash, and when finished maintenance is close to zero.

With the heater valve out, coolant flows all the time, but no heat enters the cabin as the flap door prevents it. When fall and winter comes, full HEAT arrives quickly, in a way that few cars can match.

[Opelotus]

Can you post pictures of the finished product? Might come in handy for my track car build.

[Duckworth]

Here we are..




Near the top, the upper wood is not lit well, but easily understood working the linkage with blower on, to windscreen. Dowel rod is in plain view connected, with (10 cent) eye screw at the end. Length is probably 10 - 12" altogether. Diameter must be slightly snug for feel and adjusting. Like a carb choke, but not loose style. Fwiw, a choke could be used, except that the slope of the metal is a bit of a burden, and some chokes lack a smooth feel.

Red part : Not sure where it came from, a type of male to male hose connector with a positive 'stop' at center. A few hours were needed to sort the copper piece, jb welded, to anchor the fitting. Once secured, the rest falls into place. Clearly, a leather swatch would integrate the mod better than I did, but unless you crouch, it's not obvious as above.

[JK McDonald]

Hey Duckworth - Many owners will agree with you when it comes to the problem of controlling the interior temp of a 928. Although installing a "manual flap adjustment lever" will work, many times the root problem why our HVAC does such a poor job in regulating the temp is because it's exterior air sensing thermistor is disconnected. When this signal is missing - the motorized heater door will constantly swing from full tilt "Freeze Your Cojones to Cook Your Cojones" every time you try to make an adjustment.

The HVAC control system must be able to read the outside air temp (resistance of the exterior thermistor) AND the interior air temp (interior thermistor resistance) to correctly set the temp door position.

The exterior thermistor is located behind the left fender front splash shield in the entrance of the alternator cooling hose. (Tin Can Looking Gizmo). The interior thermistor is located in the small circular sniffer vent built into the dash. The console mounted HVAC temp adjustment slider arm is a variable (series) resistance used to fine tune the total resistance value of the internal thermistor.

Surprisingly for a +30 year old system - when both thermistors are connected, the HVAC temp slider internal contacts are clean, the motorized heat flap is adjusted correctly and the vacuum solenoids/door modules are working - the 928 will do a pretty good job of controlling the cabin temp.

Good Luck - Michael

[Duckworth]

Michael, interesting stuff on the thermisters, which were long gone on my car. Glad to know guys can sort their way thru the issues that arise.

To be clear, I'm not suggesting those with original cars run to the garage and pull out actuators. But occasionally, a mechanical path can trump various electronic whizbangs in performance. Ex., because the location is under the wheel, the rod adjusts temps quickly, almost immediately...a second or two !

Imagine the shock to the public if Porsche ditched sensors in favor of a physical item for temps...it would probably be seen as lacking somehow, but imo the reverse is true.

Unfortunately, nothing gets done today unless it's circuits and solenoids, for everything. The more complexity continually sold to us, the more 'Murphy's Law' will rear it's head. Rods and levers don't often fail, but when they do the fix is fast and enjoyable.


Phil

[JK McDonald]

Hey Phil - Like you've done there are times when keeping it simple is the best way to solve a problem. One winter a friend's CTS Cadillac HVAC computer started doing weird things that disabled the heater and defrost functions. After several shops gave him a repair cost estimate of $1,400 - $1,600 (Most of It Labor) he was about ready to trade it off.

We came to the same solution you did and installed a manual "Choke Style Cable" to regulate the heater core door. It's worked great for controlling both the heater and A/C temp for several years.

Good Luck - Michael

[Duckworth]

Another Packard idea that probably few would consider but can make for nicer cruise depending on where you live with cold spells of 15' - 20' F....

Recently I decided to copy the school buses that block their air grills about 80%, and was quite pleased...so long as you're aware of it and careful to remove it promptly on days over 30' F of course. .

I have no slats in front of the rad, and the idea was simply cutting thin luann plywood section 26" wide by 14" H that goes at bottom of rad, and comes up at top of mouth area, unable to blow out.

The temp gauge does read higher of course, while the cabin receives better output of heat, in a shorter span also. The benefit is mostly felt during a late night drive as a grocery getter thrill ride.

[Alan in AZ]

There are things I don't like about the 928 HVAC but temperature control isn't one of them - it does a fantastic job of this in a closed loop feedback manner when everything is working - far better than any manual system could possibly do. I understand your system probably had some issues and this path maybe an easy fix - it is not however a particularly great one.

I live in Phoenix - in the summer the car would be oppressively hot if the heater core was always hot. If I could not focus air to the console vents only when its 110F+ outside I'd be too hot through much of the summer.

The system works fairly well when functioning right. I do wish wish the heater core wouldn't get hot every time I stop the engine. I also wish I could control the recirc & vents independently and not have to default to multiple vents open. Some other minor things too - but generally its reasonably OK when sorted.

Alan

[honerboys]

is there a test for the thermistors? - i know i can get them - what value would i be looking for? - my car can get icy in the summer with the temp control all the way to cold - in the winter if i move it even slightly to the warm side it will blast HOT air until i nudge it back to all the way cold - thanks

[JK McDonald]

Hey Alan - I agree with you that the 928 HVAC system CAN do a good job of controlling the Heater and A/C temp WHEN every component is working properly. After a lot of time and effort I finally had the Ventilation, Heater and VAC system in Miss Purdy functionally at 99% ........ My only remaining complaint was that my Factory Heater (Hot Water Control) Valve would gradually fall to the OPEN position when parked. This would allow the Heater Core to fill with hot water so on restart in the summer the A/C system must 1st dissipate the heat from this hot water before any cool air is felt through the vents.

The final solution was to install a stubby "manual" hot water shut-off valve in series with the factory heater control valve. I inserted this new heater valve into the short piece of heater hose that's between the top rear of the motor and the factory heater control valve. An accessible cut down choke type cable is used for manual control with the loose end tucked down beside radiator reservoir. In the winter the added shut-off valve is left open to allow the factory heater control components to regulate the heater temp.

In the summer this manual valve is fully closed. Now even if the spring loaded factory Heater Valve gradually opens when parked - my A/C system never has to cool off the heater core before producing cold air.

Good Luck _ Michael

[Duckworth]

Alan and Michael, I found your posts fascinating on the valve function, which I fretted over at one time, knowing the engineers did not have it as an afterthought. In other words, I had DEEP concern of unwanted heat at improper times prior to removing...BUT it never materialized when the rod position was @ 100% shut.. There were grave doubts of discovering that the Ac console vents were compromised. What a great relief when it did not happen as expected, or others found first hand.

Much has been written about it's function in the loop, which makes sense, but the car presents no heat in July of 98F, shutdown, or startup. Although in the summer, I often 'think' about the core temp...whether it will present a problem, since logic says it should be. Otoh, because there is no intrusion, I often feel relaxed, content, with this part of the car, where nothing has reared it's head from the day it was done. Like a blessing of some kind..