heater- ac

[1932]

Can i wire in a relay to turn on-off heater=ac with a toggle switch? Toggle would be with other switches behind shifter.
As in build thread.

[Svtfreak]

You mean one switch to turn both on/off?
Or one switch to turn either on (like up=ac and down=heat and maybe center=nothing?

[1932]

I was thinking on-off, but the one switch to turn eather on would be very good!

[NAZ]

I think you're looking for a SPDT switch that is On-Off-On -- where in the lower position the heater is energized and when in the upper position the A/C is energized then in the center position both are off. If the switch can handle the load you won't need a relay but most of these SPDT automotive type switches max out at 20A so if your heater fan or A/C unit exceeds that you will need a relay for one or perhaps both.

[britpit]

I hate to say that a single switch for Full-on AC or Full-on heat doesn't make sense - or I don't know what you're trying to do. Don't you want to vary the heat or coolness?

[1932]

The full controls will be on dash to set temp. Most of the time the temp will be for time of year, so just turn on. The problem is reaching the dash with harness on.

[1932]

Looks like i will only be able to turn on off.

[Svtfreak]

NAZ gave the right answer. A SPDT would be off in center (assuming you find a on-off-on pattern and not off-on-on). Up could turn on heat and down turn on ac. You might would need some diodes to prevent backfeeding the other from the blower fan though? I would have to see the wiring to sort that out and haven't gotten that far on mine.

Although, thinking about it, not sure why you would want or need that. The temp control should otherwise handle the heat side (as it's a valve) and the ac would need an on/off. That way you could run the ac to dry the air and still have heat on, to defrost, for example. I'm thinking now that an on-off for them wouldn't be needed.

[1932]

The way i read the wiring looks like heat and ac are kind of working off same feed. But i am no sparky!

[DaveS53]

A 30 amp toggle switch is easy to find and could turn on or off, all power to the entire system. If the switch was turned on, the unit would run with whatever settings the knobs are turned to. The problem would still be temp control, if you can't reach the temp adjustment and fan speed knobs. The unit will put out a lot of heat and the control is touchy.

I don't believe that the unit is sophisticated enough to run the AC and heat at the same time - it's old school, with heat for defrost and AC for cooling. The defrost knob only directs the air flow to the defrost ducts.

In normal AC operation, the compressor turns on and drops the air temp to into the 36-46 range. The compressor won't run for very long before it shuts off and allows the air temp to rise about 10 degrees, before turning the compressor back on. Continuous running of the compressor would freeze the coil. I have an indicator light on my system that tells when the compressor is on. I connected it to the wire that runs to the trinary switch. During normal operation the trinary switch passes the current on to the compressor clutch. An indicator light between the trinary switch and compressor would tell you if the trinary switch was reacting to an over or under pressure condition.

[1932]

The instructions say to run both to have dry air for defrost, more heat than ac. If i isolate the thermostat on control panel maybe that would work to turn ac on-off?

[DaveS53]

If you want to turn the AC off, you should only need to put a switch in the wire that runs to the compressor clutch. If it's a Vintage Air unit, the blower fan would still run. The knob that controls the fan speed also turns the unit on, so heat or AC can be used. If that switch is not on, then nothing will work.

You're right that the AC and heat can be used for defrost. Shows that I've never read the instructions fully.