88 C2500 Sierra Heater Problems

[88 GMC Truck]

I found that the actuator was not operating properly so I bought a new one. It is the one that moves when you slide the digital temperature controll on the dash from cold to hot and is located on the left side of the glove box in the dash. So here is my delema. With the actuator out I can manually close the gate it operates just fine. The problem is, it is not blowing HOT AIR just luke warm when it is moved to the hot or closed position. So even if I get the actuator working, it wont fix the lack of a heat problem. Is there anything else that can effect the temp on the heater system that I might be overlooking? I have noticed right behind the glove box there are 3 relays that I do not know what they are used for. They look to be in the heater wireing harnes. Any suggestions are most welcome!

Thanks !

PS the motor not running properly is the digital controll itself!

[horse482]

Are you getting full flow through the heater core? I would get the truck to operating temp and then feel both heater hoses conected to the heater core, carefully they will be hot, the out let should be a little cooler than the inlet, but not much. If it is a lot cooler then the heater core is pluged. There is not a shut off valve factory on this pickup, the core should have full flow at all times, also if your water pump is not moving the coolant through the block then there will be no heat. Hope this helps.

[offroadjoe]

hey i have a 88 sierra to but a different problem.... my heat only comes out from the top on the dash not out of the vents :S i had this problem for a year since i bought the truck lol gotta find out what the hell is wrong with it .. any ideass?