ITR 4

reconcile the 26AS with TDS certificates available with you to sort out the additional sum and deductor,

You have to claim the amount which is correct,  check the next AY tds certificates also sometimes in case of mistake from the filier it can show such amounts

THE CERTIFICATES ARE NOT AVAILABLE IN NEXT YEAR . I HAVE RECONCILLED THE DIFFRENCE . CAN I CLAIM REFUND IN AY 11-12 IF YES HOW ?? AND I DONT HAVE CERTIFICATES FOR THE BALANCE AMOUNT . ONLY ON BASIS OF 26AS CAN I CLAIM REFUND???

26AS is a statement of TDS credit, where u can get the deductor details, amount deducted, and sec, 

1) reconcile the TDS certificates available with you and mark them in 26AS - 1st stage confirmation

2) for remaining entries in 26AS, check your books entries and reconcile them, - 2nd stage confirmation

3) for the entries which are neither in TDS certificate form, nor in books entered, contact the deductor for clarification

u can claim whole amount  as per 26AS, but at the stage of correction we are afraid that proceedings would invite re-assessment u/s 143, so if there is any mismatch in your accounts get the reconcilation ready with you. 

you have mentioned only the refund amount but not mentioned the assessment order u/s 143(1) issued by department, you have to rechek the difference between your return filed computation vs assessment computation, if they have added back any entry or rejected any credit , there may be grounds for doing so.