Heater Core Bypass Mod (Tony Wa) [How To]

[t65tampa]

I took my car in to the local Lotus dealership for regular maintenance. I explained that the AC has been freezing up lately after 20 to 30 minutes of use (air going warm, volume of air pushing through system decreasing). I know this is a common problem, so that's why I am posting this. The service technician told me they have a repair that can help limit the condensor freeze that causes the problem. I will find out what the repair or fix is specifically when I pick the car up Friday.

[lucksta]

I just knew you'd nail this, Tony. Congrats

Hope someone from Lotus is lurking.

-Chuck

[Tonywa28]

The freeze-up mod repositions the thermostat pickup in the AC evaporator coils. This take about 15 minutes to do and did help my car with the freeze up, but didn't address the poor cooling performance overall. There are other issues that can cause freeze up including wrong freon amounts, poor air circulation, etc.

Hopefully your freeze-up goes away with the mod.

Good luck at that Tampa Bay dealership. I've had issues with their service.

[Tonywa28]

JnC,
I looked for quite a while trying to find the normally closed switch in the counter-clockwise postion, but no luck. For me this would have been preferable to the push/pull version I was able to find. I'm sure it could be custom made, but at what price and how many. I was hoping by posting the need on the board maybe someone else knew of a source.

FYI - when the switch is "pulled" it only moves out about 3/16 (see pic). So it's not noticeable at all.

Tony

[JnC]

I found something on digikey but I can't tell how the switch works.

Doh. Here's the datasheet.



Out of curiousity, can you tell who the manufacturer is of the OEM switch? Is there a part number to x-reference? Maybe they have some additional varieties.

[Tonywa28]

+Here's my take on whether the bypass would affect your warranty or not:

I have no clue what Lotus might say (also stated this in my installation instructions). I’d guess they’ll “not okay” it as their corporate stance. It’s difficult for them to “approve” a mod to their cooling system when they don’t know the source of the parts, the mod, or the testing. If I was them, I wouldn’t. They would take on too much liability for something they know nothing about. They’ll probably say the same thing about a CAI or aftermarket header or piggy-back ECU or adding an in-car bluetooth cellular phone system (MINI won't allow that). I’m not trying to belittle them; I just see their point of view. I’ve been on that side in the past. Also Lotus seems to be very stingy with their warranty budget (in my experience). Wouldn't pay to aim my headlights (almost straight down from the factory). No rental car during warranty repairs, etc.

On the other hand, I’d ask them what they are expecting to do as a company about their seemingly inadequate and problem ridden AC system. My car has been in 4 times for AC issues. Pinched O-rings, bad compressor (2 trips), temp sensor mod.

But would they not repair your broken transaxle because of the bypass? I personally believe they would fix it. I hope everyone is reasonable. But if they didn't, I'd be taking them right to court to prove cause and effect. But this is all just my OPINION!

Statement: I’d love to drop the whole bypass thing if they’ll just fix their problem.

[Tonywa28]

JnC,
I found lots of pots with the on/off like we want (radial switch), but they all had other problems like round shaft (a biggie). I went to the places like Digikey, Electronics Goldmine, Radio Shack, Jameco, CTS, Clarostat, Alpha, and some other manufacturers, but didn't find one that met our needs. It seems the biggest problem is the shaft. That half shaft does not appear to be common. There's are lots of knurled, slotted, round, and d-shape. The knob on our cars only fits the half shaft... You could take a round one and do some grinding, but that was something I wasn't willing to get into....and I couldn't drill out the knob, reversabilty of all mods is King for me!

Keep up the looking though, I definitely am not the authority on these parts and I appreciate the help.

[lucksta]

Originally Posted by Tonywa28

I looked for quite a while trying to find the normally closed switch in the counter-clockwise postion, but no luck. For me this would have been preferable to the push/pull version I was able to find. I'm sure it could be custom made, but at what price and how many. I was hoping by posting the need on the board maybe someone else knew of a source.

Tony

Another alternative to a push-pull switch (and one I think I'll try) is to add a SPDT relay to the standard rotory pot-switch combo which will activate the bypass when the switch is turned off (fully counter-clockwise to coldest). This does add about 1.25 oz. of weight, a couple bucks of expense and a little wiring complexity, but it makes cold air operation entirely intuitive (idiot-proof).

-Chuck

[Tonywa28]

Find attached an updated bypass instruction and parts list that addresses the installation of the push-pull potentiometer. These documents supercede the ones I posted a week or two back. I'll be contacting the webmaster to have them removed. Maybe I can get this moved to the "how to" section. I've added parts and information for insulating the vent hose and aluminum heater tubing as well. I also added some information about adding cool air vent tubes from beside the radiator that dump onto the firewall to cool it (see pic). I have little time on the car since this last mod (cool air vent) , but it really seemed to cool down the drivers footbox. More on that another time.

By the way Lucksta is absolutely right about the relay , I was just looking for a way to avoid the relay and additional wiring by trying to find a pot with normally closed contacts in the CCW postion.

Water Wetter rules....

I think I'm done.

[JnC]

Originally Posted by lucksta

Another alternative to a push-pull switch (and one I think I'll try) is to add a SPDT relay to the standard rotory pot-switch combo which will activate the bypass when the switch is turned off (fully counter-clockwise to coldest).

Definately post pics once you get it together.

[Buz]

I think the heater bypass mod should be split off into its own thread. A big deal for us down south.

[Randy Chase]

Originally Posted by Buz

I think the heater bypass mod should be split off into its own thread. A big deal for us down south.

I was waiting for Tony to finish to split it off and clean it up. It very much deserves to be separate.

Tony, I did this mod today. Thanks for everything. It was not easy, but it is done. I also repositioned the AC proble which had moved since the car was fixed before.

[qball]

We should start a club! AC Bypass Club! Tony is the founder!

I should be member #2...

[CALtd]

Originally Posted by Randy Chase

It was not easy, but it is done. I also repositioned the AC proble which had moved since the car was fixed before.

What were the hardest parts of the install and how long did it take you?

[Randy Chase]

Originally Posted by CALtd

What were the hardest parts of the install and how long did it take you?

Probably the hardest thing was finding the bits I needed. If one can wait (I can't... I cross the desert this upcoming week), then get the kit.

Finding the part numbers and getting the valve and solenoid was very easy. Had them in a couple days. I have hose clamps, tie wraps, wire, etc. I needed the proper 1/8" tubing and the tube junction.

Once I had the parts, taking stuff off is easy. 5-10 minutes. Unplugging vacuum fitting from brake booster. Simple. Cutting booster line, easy. Inserting "Y" Junction, easy. Attaching hose clamps... mostly easy, one end is captured down a bit deep. Attaching the 1/8" hose to the coupling... not so easy. It was tight!

Cutting the heater lines. Easy. Trying to make sure the valve is far enough away from the corrugated hose... not so easy. I had to trim more tube on the passenger side and even then use cable ties to pull the valve away from the big hose. My recommendation is to move it farther left than I did. But it works now.

OH... dealing with the coolant mess sucks. It was not very much in volume, but sopping it up, rinsing it out... and it made everything slippery.

Putting the hose clamps on the valve... pain in the arse. Specially since my hands were slippery and my clamps were a little too big.

Attaching the small 1/8" tubing... not too hard. The valve has a small nib.

Attaching the tubing to the solenoid thing.. sucks. Sucks dead bunnies up a straw sucks. But I mostly got them on.

I soldered the wires directly to the pins on the solenoid and then filled the entire connector area with RTV and gobbed RTV on the wires for a strain relief and then tie wrapped them back to the body of the solenoid thingie.

I already had wires running from the fuse block area to the cockpit, so that was not needed. If you did have to add one wire, it should be easy and add 10 minutes, but you also need +12V. I also already had the switch installed in my Trikster Gauge Bracket. Attaching the ground lead to the wiper motor is a good thing and easy.

I was doing some other things to the car, but I am going to guess start t o finish was about an hour. Maybe 90 minutes tops.

[pete k]

Is there a reason you cant just put a manual on/off water valve in the engine compartment? Switch it off in summer, open in winter? What is the reason water needs to circulate through those lines? It can't be engine cooling, it seems to me the recirc pump is just to get water to the heater core in a hurry on a cold day. What am I missing? Thanks in advance. Pete

[Bruce]

Originally Posted by pete k

Is there a reason you cant just put a manual on/off water valve in the engine compartment?

Guys are afraid to disable the heat soak. I'd like to know how often heat soak is actually enabled and is there a way to know.

[pete k]

Originally Posted by Bruce

Guys are afraid to disable the heat soak. I'd like to know how often heat soak is actually enabled and is there a way to know.

Thanks Bruce, that explains a lot. First, I have never heard it come on, and probably won't. 110 C is the same as 220 F, which is probably possible to reach after turning off a hot engine, although I always run my engine for 30 seconds or so before shutting it off on a hot day while I wait for the temp guage to start declining, indicating no hot spots left in the engine.

What about a solenoid operated water valve in the engine compartment which is held closed with power on it while the engine is on, and when the key is turned off it opens. Then in the winter, just pull the wire off of it. Seems to me an easier way to stop the water circulating and heating up anything. Any thoughts? Thanks. Pete

[TimMullen]

Originally Posted by Pete k

It can't be engine cooling, it seems to me the recirc pump is just to get water to the heater core in a hurry on a cold day.

Nope, the recirculation pump is controlled by the ECU. After you shut down the engine, the ECU monitors the temperatures for about 20 more minutes. If it detect that things are "heat soaking" then it turns on the electric recirculation pump to circulate water through the head to the heater core. This prevents localized hot spots.

What is not known is how much heat removal is done by the heater core, verses the lines up to the front and back again. In any case, that is the reason for the vacuum controlled valve - when the engine is turned off, the valve go out of "bypass mode" and water is again circulated through the heater core.

Making it a manual bypass valve by the engine, would defeat the purpose of the recirculation pump. Even making it automatic (like the vacuum operated on valve) might cause problems with "cold" water from the bypassed heater circuit is suddenly recirculated into the cylinder heat. That's why the bypass valve is mounted up front - all it is removing from the circuit is the actual heater core (removing it as a heat source in the HAVOC box).

It would be possible to put a manual valve in the vacuum line to turn off the bypass in the winter, and make it automatically come on in the summer if you wanted to save the effort of doing the electrical wiring. But I would think that the on-off switch would be worth the effort.

[TimMullen]

Originally Posted by pete k

TI have never heard it come on, and probably won't.

I've never heard mine come on either. But then again, I have yet to wait around for 20 minutes listening for it either. I suspect that it must be a distinct possibility that it can be needed, or Lotus wouldn't have gone to the trouble to have installed it on the car. I believe that someone had simply disconnected their heater by replacing the hoses at the engine with a short one to interconnect the in/out at the engine.

I like the safer way of mounting the bypass up front - keeps the recirculation pump/system for heat soak, and should prevent thermal shock (even if that isn't a serious problem).

But there is not reason that you couldn't use an electrically controlled valve like you figured, and mount it up front. Or use a vacuum controlled valve with a manual on/off valve as I posted above...