My A/C is blowing only hot air, as it does if I were to turn the dial to heat.

Here is a list of what I know or have checked:

• New compressor and dryer bottle this time last year
• compressor does come on when I turn on the air
• mono valve membrane seems intact, but there was some slight surface corrosion on the metal washers
• aux fan is not working, I will take it apart this weekend to attempt a repair
• not sure about the freon level (R134a)

I will try to get a photo of the mono valve up soon. What other items should I check out?

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"Gerwalt" 1984 - 300TD