Problem with direct vent furnace (long)

Hi, Our house has a 75000 BTU direct vent condensing natural gas furnace. This is our first winter here but the house and furnace are 8 years old. We've had some real cold weather lately, below zero around the clock for over a week. The furnace is running alot, however I've woke up in the morning a couple of times to find the house pretty cold and the furnace not running. The vent blower is on, but nothing else. I figured that this meant the furnace could not prove draft or exhaust. Went out side to find the inlet pipe frosted over. Cleaned it off and the furnace runs. I took out the manual to check the installation and wow the previous guy really cut some corners. First the manual states that the centers of both pipes are suppose to terminate a minimum of 8" apart( 18" min. in very cold climates, sustained below zero), mine are barely 5". The pipes are supposed to extend 8" from the building wall, mine are practically flush. The inlet is sucking in the moist exhaust air and it is freezing on the screen. He did use the right size pipes for the length of the runs and number of 90s. Back to the good news, he runs the pipes to the back of the house and underneath our deck, and the basement is finished with sheetrock so I have no access to the pipes once they leave the furnace area. Can I put a 90, pointing down on the inlet, and extend the exhaust pipe 18"? This would give me my separation, however the terminations would not be the same distance from the house.
Also will PVC primer and cement work in ten degree weather? I can make everything up inside, but I'll need to do the final tie-ins outside.
Also there seems to be quite a bit of liquid running out of the exhaust pipe, should I pitch it down some? I'm worried that this moisture will freeze with the pipe 18" away from the house.
Finally is anyone responsible for a dangerous installation like this? I know you purchase a house as is, however does an installer either professional or homeowner accept a liability when installing these things?
Thanks for your time, Jeff

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