Hi Vergie,
Thank you for your question about summer lawn repair.

In general, the best time to plant a lawn from seed is when temperatures are favorable for rapid seed germination and grass growth. In the northern part of the United States, grass seed germination is optimum when the air temperature is between 60 and 85F. Try to time your planting so there will be 6 to 8 weeks of good growing weather after seeding.

With that in mind, the period from mid-August to mid-September is almost perfect. Days are warm, nights are getting cooler, sunlight is plentiful, and day length is declining. Lawns planted during this period germinate and grow rapidly. You generally can expect to see green grass in a week, followed by the first mowing about 3 weeks after planting. 

Planting later in summer causes many problems. With longer days and high temperatures, it is difficult to keep new plantings wet enough to ensure uniform germination. If you water too much, you might encourage warm-weather disease such as pythium. Once seed germinates, temperatures often are above the range for healthy root growth. The result is grass that requires constant attention all summer.

What if you decide to plant sod? Sod has the same optimum planting times as seed, but because the grass is mature and has part of its root system, you can get away from planting over a much broader time period. Provided you have a well-prepared sod bed, sod can be planted from about April through October in much of central and eastern Oregon, provided irrigation water is available.

If you really must plant in summer the following OSU Extension publication provides some tips to enhance your chances for success.
Source: Practical Lawn Establishment and Renovation | OSU Extension Service (oregonstate.edu)

Two additional publications you may find helpful:
Lawn maintenance calendar for Central Oregon | OSU Extension Service (oregonstate.edu)

Efficient Lawn Irrigation in the Intermountain West | OSU Extension Service (oregonstate.edu)

If you need additional information, I recommend you call the Deschutes County OSU Extension office in Redmond at<personal data hidden> and ask to speak with Amy Jo Detweiler (oregonstate.edu), our Community Horticulturist. Amy Jo welcomes your home garden questions and is a great resource. She may have additional ideas for you.