Laptop recognizing only 4GB out of the 8GB installed

[LoyalPhil]

Hello community,
I need help. I have a 15-ac114tu laptop and it is only recognising 4GB of RAM memory, but it actually has 2x4GB installed.

The readings are strange. The HP support assistant shows only one DDR3 Samsung 4GB, 1600 MHz installed in "Slot 1 (left)". Info on Windows Task Manager is similar.
However, when I check it with the CPU-Z software, it shows me a Samsung DDR3L 4GB (800MHz) in Slot 1, and a DDR3 Ramaxel Technology 4GB (667 MHz) in Slot 2.
I confirmed by opening the laptop that it actually has the two RAM installed. I tried taking them out, blow some air to clean dust, but it keeps just recognising the Samsung in slot 1. 
Could it be that the two RAM are incompatible due to the difference between DDR3 and DDR3L?
It honestly is quite strange. The previous owner, who is an elderly friend whom I totally trust, assured me they bought it brand new like this. I didn't see signs of it having been opened up before either, but I could be wrong. After all, the manual says this particular laptop comes with 4GB RAM originally.

Is the other RAM not gonna work at all? Would swapping do something? (I'm a bit concerned since I read something about DDRs using more voltage than DDRL and that it could be a hazard for the motherboard, but maybe I'm totally wrong here again.
Anything at all I can do to make the laptop recognise and use the 8GB? 
Many thanks in advance!
Felipe

[TheOldMan]

Here is the manual for that model

http://h10032.www1.hp.com/ctg/Manual/c04653884.pdf

on page 46 the supported memory is listed.  It does specify the 4-GB (PC3L, 12800, 1600-MHz) that you posted

( and the spec page also shows that as the supplied memory from HP)  but it can also be 8-GB but any memory must be the type "L" and they should be matching pairs.

Therefore the the memory in Slot #2 is not compatible.