MrVette90l98mt

Hey guys I'm looking for none invasive ways to diagnose why it takes 15 minutes for my defroster and interior heater to get warm.

I've had this car for 5 years now with little to no heat until I drive for +15 minutes (my patients is up now, lol). About 2 years ago I did a cooling system over haul, 2 row aluminum radiator, edelbrock aluminum water pump, 180* stat, rad hoses, drain and fill coolant (no flush, no time and money for heater core). The controls all seem to work with the occasional intermittent no response from buttons.

Today I drove home from work and decided to check the inlet / outlet temps of the heater core. I get about a 15*F-20*F difference with engine hot, idling, defroster on, command 90*F, fan speed 10. Normal?

I assume the heater core is original as the previous owner used this think like a honda civic commuter car, fixed as things failed only. some ideas of mine:

Cliff Harris

Your temperature blend door might be stuck in the cool position. Take out the blower control module from the evaporator housing, set the temp to 90° and check the position of the blend door. It should look like this (the rusty thing is the blend door):



The air comes in through the AC evaporator (on the left) and makes a U turn and goes through the heater core and then into the AC ducts.

MrVette90l98mt

Ok, today I check the blend air door and it seems to work properly. It will block off the heater core when I command 60*F and open the heater core when I command 90*F. It'll take about 5 seconds to make the transition. it will stop somewhere in the middle if I command ~75*F. To my surprise my heater core and evaporator look new!!! No corrosion or signs of leaks!

Another thought I had while checking the blend air door-When I did my cooling system overhaul, I can't remember if it was mine or if it was somebody else's car I was working on, had the heater hose fitting on the water pump had a built in restrictor. Now stating the obvious: if the heater hose fitting on the water pump was restricted how much of a difference would it be in heater/defroster performance? Is there a reason for the fitting to have an integral restrictor? I looked at my heater fitting on the water pump and I must have reused the fitting as it looks original with minor rust.

Thanks in advance!

Cliff Harris

My car has a restrictor in the fitting on the front of the intake manifold that the throttle body coolant hose attaches to. The hole inside that fitting is about 1/4" diameter.

I know that in later years (LT1s?) there is an in-line restrictor in one of the heater hoses.

Can you change where the air comes out of the AC ducts? If not then your vacuum check valve is probably bad.

MrVette90l98mt

Yep, all is well. I can command any combination of the vent position and temperature/speed. I plan on doing a coolant flush using prestone flush, let it soak for a couple of days, check the flow through the heater core while its drained, and maybe change the restrictors in both the intake manifold and or water pump just to see if I can improve cold start heater performance.

Does anybody know how fast the heater/defroster is suppose to get within a certain time?

It takes about 15 minutes of city driving before my heater gets to ~100*F. My defroster has limited performance as my A/C has no charge and won't turn on the clutch (clutch works if jumped straight to battery) so i'm hoping if I can get more heat sooner my defroster should work better.

desertmike1

your heater core might be obstructed, this happened to me, try back flushing the heater core with a garden hose, be gentle and don't allow any pressure to build up or you might damage the core. If you feel the hose's going into the core they should be nice and hot.

Cliff Harris

What does your dash coolant temperature display say while all this is going on? Mine gets to 100° in about a minute of running.

Is your thermostat missing?

MrVette90l98mt

Yeah I'm starting to think that even though it looks new from inside the HVAC box. But the odd thing is after a 15 minute trip both heater hoses are piping hot and I get a 15-20 (~180-165*F) degree difference with a temp gun.

The temp displayed on the dash has always been on the slow/cold side ever since I've owned it (5 years). I originally thought the previous owner had a 160* stat because he lived in Nevada. Around 2 years ago I did an overhaul and replaced the 180* stat (to my surprise) with a new stant 180* stat and drilled a 1/8" hole to help bleed the air. ever since then there really was no difference in heater / defroster performance. Tomorrow i'll drain and check the heater core flow and try a flush and clean, coolant is starting to smell funny but still clean.

The funny thing is I've owned a 2000 S-10 2.2L 4 banger since new and that has the best heater/defroster of all my cars. literally within a minute the temp from the vent is already at ~100*F. A month and a half ago I bought a 4 door corvette (2009 Pontiac G8 GT ) and the defroster gets ~100*F in about 3 minutes. I have no idea what the cooling system state is other than the Dexcool is ready for a change as well (5 years). So odd that a tiny 4 banger has better heater / defroster performance than 2 V8'S