dailydriver

I just removed my whole under hood AC system (except for the stuff in the firewall/dash), due to; too many parts not functioning, cost of repairs/replacement, and to save weight off of the front of the car (better weight distribution).

Just how much does this effect the efficiency of the front defroster?
Does it just slow de-fogging the windshield when it is humid, or people are in the car breathing out warm CO2, or does it actually slow down the exterior frost/ice melting to a great extent??

Thanks in advance,

Dave H.

01ssreda4

iTrader: (96)

It heats the window but doesnt dry the air inside the car. It will probably de-ice it the same (ice is on the outside) and de-fog it not near as well (fog is on the inside). Thats just a guess though....

RPM WS6

iTrader: (3)

This is exactly the case, based on the experiecnes I've had with cars that either didn't come with A/C or where the A/C was broken.

Remember, in very cold temps the compressor will not engage even if it's present and in working condition. It's designed to NOT engage below a certain temp, so you can turn it on defrost but the compressor won't engage if that minimum temp isn't reached. Even still, the warm air will melt the ice/frost, and when it's very cold the air is usually dry enough that fog won't be much of an issue either way.

In warm, humid weather, the defog feature will be mostly useless without help from the compressor.

dailydriver

Thanks to all above.

RPM WS6, thanks for that info about the compressor not engaging below a certain temp, as I always thought that it ALWAYS engaged when the controls were set to defrost.

Do you happen to know the ambient temp which will prevent it from engaging?

01ssreda4

iTrader: (96)

Well that would be whatever the car is programmed to. Before the computer controlled AC clutches, I can promise you they were always engaged regardless of temp because the contactor was in the switch itself, the computer was not part of the equation....talking very early fuel injection. As for carbed vehicles, I've never heard of an ambient sensor for AC, only ones for pressure which are a byproduct somewhat of ambient but under hood temps would greatly effect that.

RPM WS6

iTrader: (3)

It's been awhile since I've had a old carb'ed car with functioning A/C, so I dug out my '71 chassis manual just to confirm, and found this in the A/C section:

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"When the system selector lever is placed in the A/C, DEFOG or DEICE position, electrical circuit connection is made to the compressor clutch through the control panel switch and the ambient switch. If the ambient switch is closed (ambient temperature above 40°F.), the compressor will run. [15-34]"

"NOTE: Each switch has a 15° range, 25° to 40°F (Chevrolet)

The ambient switch prevents the compressor from operating when the air temperature is below 25°F. This switch is located in the blower and evaporator case as illustrated in Figure 38. [15-54]"

"AMBIENT SENSOR (Fig. 72) - The ambient sensor measures the temperature of the air entering the evaporator core.

AMBIENT SWITCH (Fig. 72) - The ambient switch operates the air conditioning compressor switch. When the temperature at the switch is above 40°F., the compressor must be on. When the temperature at the switch is below 25°F., the compressor must be off. This switch is mounted on the blower side of the evaporator case. [15-69]"
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So it seems that there is an ambient sensor/switch for the old carb'ed setups. I'm sure a similar situation existed for early EFI cars as well.

I don't currently have the service manual handy for the 4th gen F-platform cars, but I can tell you that mine never engaged on a cold start when the outside temps were below freezing. I'd imagine that somewhere around the same temp range as used decades earlier is probably sill the case even on these later models.

01ssreda4

iTrader: (96)

Well since Im in the south I have limited knowledge of below 25 degree weather, however I was still under the impression no such ambient temp sensor existed on an OBD1 or carbed vehicle. Learn something new everyday

RockinWs6

The 4th gens don't use AMBIENT sensors or switches, if you look closely you will see a pressure transducer, this sends a varying signal to the computer telling it what's going on pressure wise. The computer then uses this information to turn the compressor on or off.

I just noticed on my WS6 If its below 30 degrees and I'm moving the compressor may shut down.

idahoz28

iTrader: (2)

Cars had defrosters way before they had a/c and it worked just fine. I am from Idaho and we have some of the worst weather in the country during the winter