question Zetor 6340, cold weather (-20C) no steering (steering wheel free turning)

HI
We've had minus 20C and lower temperature for the past few days. Started tractor but have no steering, steering wheel is free turning. Any suggestions on what to look for ?. The power steering reservoir in front of rad was emptied last summer and refilled with red, I beleive, ATF liquid...The level indicator on the reservoir is at the proper level... Thanks for any advice
Add info, Newbie to tractors, 1998 6340 purchased a year ago. Also have a 7211 with very frozen doors at this point, from freezing rain before the deep freeze...

HI
We've had minus 20C and lower temperature for the past few days. Started tractor but have no steering, steering wheel is free turning. Any suggestions on what to look for ?.

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That is cold weather you having, was the tractor left out or have you got it indoors? In this part of the world - 8 is about the max it goes but we get wet fog frost so the doors and windows freezing is common. So if you have moisture in the system this could frozen now

I had the oil pump frozen on the 5245 due to oil contamination, shifted it to neutral and let it idle for half an hour. Then i changed the gearbox oil because it was contaminated from the watered down oil from a hedgerow tractor that.had operated the same logsplitter.

I had the oil pump frozen on the 5245 due to oil contamination, shifted it to neutral and let it idle for half an hour.

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We had in the past water found in oil of backend in Same 130, Also diesel froze in several of our tractors when there was winter/ summer versions of diesel supplied, thankfully now there`s only winter version all year round available