'87 B2 - Want A/C & Heat

[CraigK]

I have an ’87 Bronco II with A/C. This has the separate push-button to engage the A/C mode. Right now (winter, cold and wet) if I am directing heat to the windshield during cold high humidity conditions (last night was pouring cold wet rain/sleet), I get windshield end and side window fogging. If I push the A/C button, the compressor will not engage while the temperature control is set to warm or high, so I am unable to de-fog the windshield and interior while warming the vehicle. Two questions:

1) Is this normal? (The A/C not engaging unless the temperature control is set to cold.)

And

2) If the answer to 1) is yes, (sounds logical), is there a way to install a switch so that I could engage the A/C (fool it) while the controls are set to warm or hot so that I can warm the interior and windshield and concurrently use the A/C to knock down the interior humidity?

Any insight appreciated. Thanks.

Craig

 

[MAKG]

On an '87, A/C control is completely independent of temperature control, at least from the factory. And no RBVs turn off A/C in heat positions. Quite the opposite for later models, for the reasons you want it.

So, the behavior you are reporting is not normal.

 

[CraigK]

Hmmmm . . .

What switches the A/C compressor clutch on and off when the A/C button is pressed?

With the fan on full, the heat (temperature slide) on the highest setting, the 'mode' on windshield (air to top-off-the-dashboard windshield vents) I was not getting any A/C help with the humidity (fogging up). Is there a 'mode' setting, or some other way to set up the climate control to get A/C to help with defogging while warming the interior and windshield?

CraigK

 

[MAKG]

It's supposed to just do that....

The compressor clutch is controlled by a pressure switch connected to the accumulator/drier, and a wide-open-throttle relay. Neither of which knows anything about the heater.

Any chance your heater core might be leaking? That's about all I can think of that would fog mostly on high heat settings. It smells distinctly sweet when this happens, and may drip on the passenger's feet.

It wouldn't be a big leak or you just wouldn't be able to see at all.

 

[CraigK]

MAKG

I have just replaced the heater core. Everything in the heater core department is A-OK now.

When I use the A/C in the summer, the amount of compressor cycling depends on how cool I have the temperature setting. If I have it on the coolest setting, it pretty much runs non-stop. If I back off either the temperature (to a warmer setting that still requires cooling) or turn the fan to a lower setting, the A/C clutch engages less, and less again if I further decrease the cooling setting (temperature slide up slightly higher). Because of this I thought there was a temperature controlling circuit as well as the two you mention. If there is not, how does the A/C unit regulate between off and full on? How would the accumulator/drier switch provide a 'medium' cool level of A/C?

CraigK

 

[RobbieD]

This is from the 1987 shop manual:
"CAUTION: During cool or cold weather, there may be a tendency to develop fogging on the windows if the outside air door is in the 'Off' position (note- Off is also Max A/C). To reduce potential fogging, place the air door lever in 'Vent-Heat-A/C' position."
If you haven't had the air door control set as this says when running the defroster, maybe just that will cure your fogging (hope so, anyway).

Without reading through the section in depth (it's titled "Manual A/C-Heat System", BTW), I don't know if systems of that vintage automatically kick in the compressor for the "Defrost" setting or not. But it looks like there's only the A/C push button, and not an additional microswitch on the function slider, like later models have to kick on the compressor when Defrost is selected.

Might be worth it to scrounge up an owner's manual for that truck, to see if there's any special instructions for the climate control system operations. The statement that I copied above is all caps and bold type in the shop manual.

 

[CraigK]

RobbieD

Thanks for the info. I looked for my owner's manual, but suspect it is long gone. I'm just starting to drive this vehicle again after not doing so for several years, so I'll have to play with different settings under cold & wet conditions to see what works best. I'll also test the A/C button again under cold conditions. Perhaps the system (converted to R-134a last summer) is just low on refrigerant and the A/C was not kicking in due to the pressure switch MAKG mentioned.

CraigK

 

[RobbieD]

You're welcome. Hope that it's helpful, and good luck.