Date: 201703
Local time of day: 1801-2400
Location: VNY.Airport, CA
Flight conditions: VMC
Light: Daylight
Aircraft: Helicopter
Operator: Military
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Cruise
Airspace: Class D VNY
ATC / advisory: Tower VNY
Second aircraft: Gulfstream Jet Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local; Supervisor / CIC
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Distraction
Second reporter function: Other / Unknown
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: Environment - Non Weather Related; Human Factors; ATC Equipment / Nav Facility / Buildings; Airport; Staffing; Procedure
Primary problem: Staffing

Narrative: I was working Clearance Delivery; Flight Data and was Controller in Charge. Training was being conducted on Local 1; 2; and 3 combined. We're in a temporary tower. 80 degrees outside. Air conditioner was NOT WORKING AGAIN! Portable fans were up giving some relief. Maintenance Techs came up later and used a temperature meter saying it was over 90 degrees in some parts of the tower cab. Local requested Local 3 be split. I called a body up to relieve me on Clearance/Flight Data.I am now working combined Controller in Charge and Local 3. Aircraft Y at 1900 feet called about 7 miles southwest requesting a transition east bound on the 101 freeway. A [military] helicopter (Aircraft X) was already in the area patrolling at 1300 feet which I called traffic. There was an unknown aircraft westbound 101 freeway about 2 east of the helicopter around 2300 feet. After all traffic conflicts were resolved I started to formulate a new watch rotation since I had to bring somebody up early. I noticed the helicopter at 1900 feet about 1 1/2 miles southwest of VNY when I saw Aircraft Y tag on the radar departing near the 101 freeway around 2200 feet turning southeast bound via the SID. Once I realized I never restricted the helicopter to 1300 feet for the transition (we are authorized higher due to terrain south of the freeway) I did call traffic (which should have been a traffic alert) and the helicopter respond with a 'yeah'. Once the helicopter turned southbound they asked to mark the tapes. I had to ask the helicopter to say again about 3 times because I couldn't understand the request. At this point I put in the request for the pilot inquiry. Due to being in the temporary tower and only 5 people are permitted in the cab. Training was in progress and the air conditioning was out of service again. Inside the tower cab was over 80 degrees and working combined positions. For some reason I didn't restrict the altitude of the helicopter like I always do. That was a mistake on my part.


Second narrative: [Report narrative contained no additional information.]


Synopsis: VNY Tower Controller working as Controller in Charge in addition to Local Control forgot to restrict a helicopter's altitude resulting in a NMAC.