1969 Mark AC Questions & Follow Up

Hi Bill –
Aircon blows cold initially and then warms up. No leaks, compressor is good, suction port gets cold. Seems a door is partially closing too. TX valve is new. Heater tap is wired shut. In the evaporator is a capillary switch. If I remove this from the evap to outside it, or bypass it, will the system think its really hot and just do fully cold? I don’t care about climate control, on a 40C day all I want is max cold. Thanks.
Gary
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Hi Gary –
Plus 40 c is real hot. If you are not interested in repairing the climate control properly, do not have a manual, have a GOOD WORKING refrigeration system and want cooling only, you can simply bypass the heater core hoses under the hood at the firewall. The Water Valve may not be shutting off internally. You may also want to wire up the damper doors under the dash to direct the air out of the a/c outlets.
I have never done this but we have seen some vehicles that have the a/c working this way for relief from the heat. Repairing the Automatic Climate Control can be difficult even with the shop manual. The above should work for you and provide the cool air as you are indicating.
Sincerely,
Bill
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Hello Bill –
I was in southern England one July day in 2017, it was 29C and people didn’t know what to do with themselves. Drink fridges in shops weren’t keeping up because they had not been designed for that temperature. If the US auto industry was based in Arizona I am sure their ACs would work properly. As it is they work alright for warm day in Detroit, totally inadequate. We do get days over 40C every summer. I have a friend in Townsville with a Mk IV and same issues. On my Lincoln I have wired shut the heater tap, so rule that out. It is not the obvious reasons. The AC works initially, then for some Detroit-thinking reason, it decides that it’s too cold, close some door. I haven’t found where it physically is in the car yet.
I also have a 64 Cadillac, not on the road yet, it has factory climate control, I am expecting the same from that. This capillary probe in the evaporator, what does that do?
Regards,
Gary
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Hi Gary –
That capillary tube and switch is known as the De-icing switch. It has two functions. It will cycle the compressor as needed in order to prevent ice build up in the evaporator coils. These cycling periods depend on the temperature of the ambient air intake through the evaporator and the blower fan speed. If the blower speed is low, the passage of air in the evaporator is slower causing a lower temperature at the capillary tube. The other function of this switch is to hold the compressor clutch power off during the winter temperatures.
I cannot rule out the wired shut water valve ( heater tap )as a problem that you already have installed to prevent coolant flow through the heater core. These valves are well known because of age etc. to not seal well or not at all because of failure at the valve and sealing area in side. Bypassing the heater core however will ensure a positive shut off. You stated in your first blog letter that you do not care about the Climate Control and that you only wanted ice cold air. The suggestions that I wrote for you are to help satisfy these desires. Best of luck to you with your project.
Sincerely,
Bill