What I did to keep recirculated cool air longer was a heater core bypass. I posted this a few months back and took pictures. Others have also done the bypass and posted detail photos on the simple job. At hybridfest, I did the bypass on Debbie Katz's FEH while her vehicle was on display at the fair. It only took a few minutes and it will only take a few minutes to reconnect when she needs the heater again. None of the factory hoses need to be cut, just use two 5/8" heater hose 90's and a small piece of heater hose, two plugs and two clamps. When things cool down, just slide the hose off and plug the core and raise the hoses high so you don't lose coolant. Have the 90's put together before removing anything and just slide the bypass onto both ends of the two hoses. I used the existing two clamps to connect the factory hoses to the bypass. Also used a tie wrap to secure the bypass to the heater core nipple. Got the parts from the local auto store for about $12.

You still must run the engine and compressor to get things cooled down, but you can stay in EV much longer. The battery also performs better because keeping the cabin A/C on when the engine is running allows the battery to stay cooler. What I'm saying is the battery doesn't have to get that hot before demanding A/C cooling.

GaryG

 

Would such a thermostat be used to make you comfy, or the HV battery comfy. Both use the same A/C compressor.

 

If you believe the Ford manual, they do cycle the compressor based on the low side pressure sensor and the downstream evaporator temp sensor. They also use cabin air for the battery A/C if you are in re-circulate mode.

 

If they cut off at 40 deg you would never get the car cold. (duct temps in the mid to high 50s) The old r-12 systems were typically set at 32 psi but the new r-134a is 29 psi. This is for the cycling clutch orifice tube systems (CCOT) which the FEH has for the front system.
They have not released the technical data for the 08s and there is barely any (aftermarket) for the 07s so I don't know anything about the 08s. But it would be a major step to cycle the compressor. Most auto temp control systems and the ones ford has used in the past still blend heated air, just automatically. Cycling the compressor would cause the compressor clutch to wear allot faster though.

 

Yes and this is to prevent evaporator from freezing, not to controll cabin temp.

 

me comfy but the HV ? This is my only worry, I dont know if the HV battery cooling system would be affected. My thoughts are that since it is a expansion valve system and most likely MUCH smaller it would be ok. Again you would not be cutting the compressor for that long maybe 1 or 2 min then on for 1 or 2 min.

 

You're right, the number I was remembering was for duct temp, not evaporator temp. The traditional duct temp in most systems used to be 40°, give or take. My mistake.

 

But this is what I'm thinking have an adjustable thermostat to shut the compressor of via the pressure switch when the evap temp reaches 40 to 45 deg. giving you an effective high 50s low 60s duct temp this would be perfect for crusing in an already cooled interior.

 

Once you shut the compressor off the evaporator temperature will continue to decline as a result of the fairly high volume of liquid refrigerant already in the compressor's downstream pipeline.

remember that at or near the point of refrigerant conversion, the expansion valve, from a liquid to a gas, vapor, the temperature will be sub-freezing.

You would need to use a "lookahead" computation based on inlet air temperature just upstream of the evaporator, blower speed, liquid refrigerant storage capacity downstream of the compressor, etc, etc.

Basically you will need to shut off the compressor based on computing how soon the evaporator's average temperature would decline to 40-45F.

Like having only ONE braking level, BHP, available and having to predict when to apply the brakes in order to come to a complete stop just before the stop sign, and not after.

 

Not really that complex, you just make it adjustable so you could tune it, install a switch to enable/disable the mod, put the sensor in the return air duct or one of the outlet ducts and design a controller with an adjustment and a delay to keep it off/on for at least 2 min. The electronics are over my pay grade for designing but I understand what is needed and the old toyotas used to control their evap temps with a similar control system.