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Hummer Knowledge Base

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Bypassing the Heater Core

Flow on a 93 and 94 are as follows: ( I assume later years are the same) From crossover through volume control valve on passenger valve cover to nipple on engine side of passenger footwell. From different nipple on engine side of passenger footwell to aux core inside Hummer. (to get at these nipple connections, you will probably need to remove the air inlet tube from the air cleaner to the intake). From aux core through hose on engine side of passenger footwell to water pump inlet.

To bypass the main core in the passenger footwell you only need to remove the hoses from the nipple connections to the main core and splice them together with a piece of 5/8" OD tube. To bypass both heater cores, just run a piece of 5/8" heater hose from the connection on the crossover to the connection on the water pump and pinch it off so flow is minimal. Better would be to plug the connection on the crossover and the connection at the water pump. Hope this helps.


2 possible places to bypass:

  1. To still allow heat to the rear aux unit......get a hose coupler (5/8" I think) and 2 clamps. Pull the hoses off where they enter into the passenger side enginewall, just below the expansion tank and join them with the coupler. Its kind of cramped down there.

  2. An easier bypass.....connect the waterpump outlet to the crossover pipe, bypassing everything.

    Disconnect the inflow and outflow hoses from the heater core at the firewall, remove the one which has the valve at the other end, loop the opposite hose back to where the first hose came from.....

    Scott Weiser

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