My heat is still only warm. I changed the thermostate (195 degree) antifreeze, and temperature sensor. Now my ac compressor doesn't kick on. I removed the connectors next to the thermostate housing for better access to the sensor. What is that connector for next to the thermostate housing? Bottom line my heat is warm at best. Nothing in my Haynes manual shows what that is next to the thermostate housing. Any help would be appreciated!!

 

Bet it had Dexcool in it at some point in time.

Sometimes it can gel especially if it gets mixed with some other type.

 

Yes it did have DEX in it. Maybe I need to backflush?

 

I normally am big on flushing but after paying nearly $1000 for a shop to tear my dash apart and replace the heater core in the 2002 I am a bit less agressive.

In the 1998 S10 project truck when we replaced the engine we went with a knew radiator due to throwing a rod and spinning some bearings and the used engine had clean antifreeze in the block. The old coolant was nasty so while the engine was out we just slid the heater hoses back on and blew out the dirty water then filled with clean water and blew it out by mouth twice and called it quits. It was easy to blow the water out so I knew it was not blocked as bad as I had feared at 524,000 miles.

Since the New Years engine/transmission transplant we have out about 1000 miles on the truck without a hint of antifreeze smell in the cabin.

 

Dexcool isn't the issue..it's mixing it with regular antifreeze which tends to create a gooey sludge. Doing a normal backflush of your cooling system will not normally unclog a heater core. This is because the water will just find the easiest path out which is your radiator. The method most of use here is to disconnect both heater hoses on the firewall, connect short pieces of garden hose to each one then alternate with water pressure between both sides until water freely flows in both directions.

Ensure that your water pressure is less than 50lbs or it could blow a joint on the core. It could actually blow it below 50lbs if it's starting to corrode but since but well all know that things rarely go wrong when we're working on older vehicles. Do we have a Wink-a-con to stick here? An alternative is taking it to the dealer for a complicated chemical flush.

There's also a possibility that there's just air in the core preventing a full water flow which can be eliminated by "Burping" the cooling system. FYI the thermostat has little to nothing to do with your heat and really don't know why everyone changes it. I start getting pretty good heat as soon as my temp gauge starts moving above the 100 degree mark so if your temp gauge is near normal and you don't have heat it "Aint the thermostat". Perhaps if you live in Nome Alaska and your thermostat is stuck open and your temp gauge doesn't move you can say the lack of heat is the thermostat.

 

I had a "flush and fill" done at the same time. I guess the flush was just the radiator, no back flush. Still have the issue with the ac compressor not coming on after I changed the temp sensor

 

You call that a flush...this is a flush or is it a knife..I think I watch too many movies.

GM Service Informatio - Dexcool System FLush

 

The A/C compressor will not turn on if the PCM determines the temperature outside is too cold, based on inputs from certain sensors (i.e. OAT sensor, if equipped). Also, if your temp sensor is defective the PCM may interpret that as "engine too hot" and not allow the compressor to operate.

 

50 PSI of water pressure is 3x the normal operating pressure. On the 98 S10 that we did the engine swap on I just blew out the dirty coolant and refilled it by pouring water in to the heater hose and repeating a couple times. After spending nearly $1000 to get a new heater core for the 2002 Blazer I know how weak these can become due to the Dexcool problem that GM lost in court.

 

Gently flush out the heater core; alternate between the two hoses until you get clear water out. This will be very messy.

This could also be the temp door is stuck. For this you would need to find where the door pivots at....sorry I am no help on this one.