Modifying AC Kit (In Squareback)

[nogoodwithusernames]

Alright folks, looking to get some feedback regarding an idea of mine. I've got a Gilmore enterprises AC kit for my Squareback, and I am contemplating setting it up to run as a heat pump also. (T4 engine conversion with homemade stainless exhaust manifold so no heat currently...)

To start with I'll summarize my knowledge:

I know I'll have to source another evap valve, a couple check valves, reversing valve, and a two way drier.

The kit as it is, seems to have a thermostat dial that has a cap tube (??) running to the evaporator to control when the system need the compressor or not, as well as of course a fan control switch. (This is speculation on my part based on what I've observed so correct me if I'm wrong.)

Now for the questions.

Once I get the system setup mechanically, how do I run it??

Fan control will obviously still work, but what about switching between heat and AC? Would I need an additional thermostat to control it in heat mode or can I source something that can do heat and cold control?

I thought up some crazy contraption where two differently calibrated thermostats are connected with some 3D printed gearing system so that it's setup to seamlessly switch between the two but that seems far fetched

Also where should I source parts from?
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71 Squareback, 1.7l T4 w/ crank trigger fuel and spark
(Conversion thread https://www.thesamba.com/vw/forum/viewtopic.php?t=732508&highlight= or https://shoptalkforums.com/viewtopic.php?f=1&t=151375&sid=f0542d44a322d290c29d6609fac7f215 )
74 914, 2.0L w/ D-Jet

-Derek

[jeffrey8164]

I’ll say first off, that I barely know how a heat pump actually works, but I do understand the theory.
My simple mind envisions two buttons. One button to engage the A/C system and a second button that energizes whatever relays are required for reversal. Similar to the O/B terminals on a heat pump thermostat.
I can’t speak to any specific temperature control. Every Heat Pump thermostat I’ve seen runs on 24V A/C.
I had an old Honda back in the day that had A/C added. It was basically on or off with different fan speeds.
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Volkswagen!
Turning owners into mechanics since 1938.

“Let he that is without oil throw the first rod”
(Compression 8.7:1)

[Mispeld]

Interesting topic. I often wondered about a heat pump in a car since I own two diesel cars, a diesel truck and of course my ACVW. But I live on the coast of NC so heat isn't too important to me. I was more interested in the concept.

I am no expert on vehicle AC's but I did work as a certified HVAC service technician on residential/commercial.

In residential - the reversing valve is normally operated when control voltage 24VAC to the reversing valve is turned off (some are opposite but the theory is if anything fails the unit will be on heat mode). The evaporator and condenser will both be the same but will switch jobs meaning the evap will now become the condenser and vice versa. You shouldn't need any extra coils. So to switch between AC and heat would simply be one wire energized or not to the reversing valve. You would have to make sure the reversing valve can work on 12VDC.

I would think the hard part would be to source bi-flow expansion valves to work with 134a pressures. I would want a TXV for the evaporator side but one that could be bypassed in heat mode and perhaps a piston type expansion valve for the condenser coil. I wonder how a piston would handle the RPM fluctuation/pressures/flow of the compressor?

Another area of concern would be the condenser coil icing over in heat mode. I am sure if your savvy you can install some type of timed relay to switch to AC mode to defrost the coil while the blower motor turns off. I suppose replacing a residential type defrost card with some type of mechanical relays and such?

I doubt you would need a thermostat unless your looking for a fancy climate controlled vehicle like that of a new car where you can set the temp. I have never worked on RV's, but maybe they run off of 12VDC?

The concept isn't rocket science, but is it worth it? A heat pump in any water cooled vehicle is pointless in my opinion. Could be interesting in a ACVW but I don't think the juice is worth the squeeze. I had a fastback in the 90's and that heat was great. It melted a cheap 12v plug-in compressor I had on the floor behind the drivers seat. I would rather run stock heat with no loss of HP rather than running a compressor and dogging the 1600.
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Tom
1977 Westy. 2.0 Fuel Injected.

[nogoodwithusernames]

[Mike Fisher]

Easier to just put stock heater boxes on it like the Germans designed it.
Keep heating/cooling separate!
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https://imgur.com/user/FisherSquareback/posts
69 FI/AT square Daily Driver
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[KTPhil]

It might make an interesting exercise in "conversion losses" as we go from chemical to pressure to inertial to phase change and back, instead of using the original waste heat to achieve the end result directly!

[Erik G]

[Mike Fisher]

[KTPhil]

There is a thread about making custom heater boxes using steel wool or equivalent. Can't find it right now...

[nogoodwithusernames]

Guys, guys, it's alright, you both think heater boxes are the best option eh? Let's leave it at that, enough junk in our lives as-is let's stay focused on our VW's here.

I was picturing in my head painstakingly TIGging each fin onto the header pipes which would take eons, but if I can wrap in a coarse wool like stainless scrubbers... That opens up the heater box option as much more feasible. Skins would be fairly easy to fab up and then source some 914 flapper boxes and it'd about put itself together. And likely a fair bit cheaper than sourcing extra parts to convert the AC.

If anyone has a link to that thread I'd appreciate it, and I'll so some searching for it as well via google.

This is exactly the kind of feedback I was looking for. Yeah it could be a neat project to do a heat pump but I just want the easiest and cheapest heat source I can get. Cheers to you all!
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71 Squareback, 1.7l T4 w/ crank trigger fuel and spark
(Conversion thread https://www.thesamba.com/vw/forum/viewtopic.php?t=732508&highlight= or https://shoptalkforums.com/viewtopic.php?f=1&t=151375&sid=f0542d44a322d290c29d6609fac7f215 )
74 914, 2.0L w/ D-Jet

-Derek

[Erik G]

[mark tucker]

why wood you need another evaporator?? just bypass the expansion valve.and add one to the condenser that can be bypassed could also pull some heat off the oil cooler or just use a heat exchanger. I dont see it being that hard to do. kinda like riding the vapor in reverse.....with a few extra parts. you could also make a hot water heater.just make the J tubes from stainless add some finnage and a tube around them welded & sealed good add fittings&anitfreezze&pump. you may also need a external core to run in the summer so you dont boil the liquid & cook nutten. inner cooler pump should do the trick. or....put a waterboxer engine in

[air-h2o-air]

Once completed you will have a window fogging issue due to recirculating interior air to heat....add that into your thoughts

[mark tucker]

bring in some out side air for the heat/ac will help. ac de fogs a lot better than heat.

[nogoodwithusernames]

[nogoodwithusernames]