Cameron you can pinch off both lines going into the heater core . You will loose some fluid from the heatercore but you can keep that to a minimum y putting a plug in the core . the reason you need to clamp of both sides is coolant will come from the other line out the core . Next when you clamp off the lines make sure you cover the lines with another piece of hose so you dont damage the heater hose . I use a small set of
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[https://www.2carpros.com/images/articles/original/fuel-line-coverd-vise-grips.jpg|needle nose vise grips with fuel line] over the ends to keep the hose metal contact to a minumum . you can also get [https://images-na.ssl-images-amazon.com/images/I/61oSeTdtzuL._SX355_.jpg|hose pinchers] that work ok at your local auto parts and tool store
Cameron you can pinch off both lines going into the heater core . You will loose some fluid from the heatercore but you can keep that to a minimum y putting a plug in the core . the reason you need to clamp of both sides is coolant will come from the other line out the core . Next when you clamp off the lines make sure you cover the lines with another piece of hose so you dont damage the heater hose . I use a small set of
[https://www.2carpros.com/images/articles/original/fuel-line-coverd-vise-grips.jpg|needle nose vise grips with fuel line] over the ends to keep the hose metal contact to a minumum . you can also get [https://images-na.ssl-images-amazon.com/images/I/61oSeTdtzuL._SX355_.jpg|hose pinchers] that work ok at your local auto parts and tool store