No Heat or Air???

jimspinnin · Nov 26, 2009

Hi, I am new to the forum. I have an 89 Mustang GT convertible and when I put on the heat it is blowing air, but not getting hot. My AC also does not work, any suggestions? Thanks

jrichker · Nov 27, 2009

Look for vacuum problems in the plastic lines that control the airflow.

Make sure the fan runs - check fuse & fan speed switch.

If the fan runs and all the fuses are good, the A/C may be low on refrigerant. To test, remove the electrical connector from the dryer/receiver (quart sized alumimum tank mounted on passenger side firewall). Jumper the two connections inside the wiring harness side of the connector together. This allows the compressor to engage in spite of low pressure/no gas in the system. Do not do this for more than a few seconds, since there is insufficent oil/refrigerant in the system to properly lubricate the compressor. If the relay and other electrical items are OK, the compressor clutch will engage and turn the compressor.

Diagrams courtesy of Tmoss & Stang&2birds
HVAC vacuum diagram

Fuse box layout

jimspinnin · Nov 27, 2009

The fan seems fine. It runs and the switch changes speeds of the fans. I am more worried about the heat with the time of year and it getting cold. lol thanks for the info.

BlackGT89 · Nov 27, 2009

Is this your first winter with the car ? If so, look on the firewall and make sure your heater hoses are still hooked up to the heater core. If not, then maybe it was leaking and someone bypassed it. If it's still connected, then make sure the hoses are hot going into and out of the core and it has good circulation. If one is hot and one is cold, maybe the core is stopped up or has poor circulation. If that's the case, you might need a new heater core. I would tackle the AC next spring...

jimspinnin · Nov 27, 2009

Well, I have had the car almost 3 years and the AC and Heat never worked since I had it. It sat for some time and finally this summer I replaced a bunch of stuff on it to get into good running condition. I want to continue to drive it as long as there is no snow on the ground and we don't usually get too much but it gets cold as all hell.
I checked the two hoses today and both are connected. The one on the driver side seems hotter than the one on the passenger side. It is warm, just does not seem to be as hot.

Repostyle · Nov 27, 2009

Assuming the car is running at normal operating temperatures, I would say you need a new heater core. Or, the vacuume lines from the switch are pinched, blocked or leaky, allowing you to change the fan direction, but it might be stuck on a cold setting.

Repostyle · Nov 27, 2009

PS. The a/c could be one of two things, either the pump has gone out and the clutch pulley isn't engaging or you need a re-charge.

BlackGT89 · Nov 27, 2009

jimspinnin said:
Well, I have had the car almost 3 years and the AC and Heat never worked since I had it. It sat for some time and finally this summer I replaced a bunch of stuff on it to get into good running condition. I want to continue to drive it as long as there is no snow on the ground and we don't usually get too much but it gets cold as all hell.
I checked the two hoses today and both are connected. The one on the driver side seems hotter than the one on the passenger side. It is warm, just does not seem to be as hot.

Maybe you could check to see if the doors are operating properly as jrichker described above and if they are then it is obviously something else. Of course the heater core is just acting as a radiator of a sort, so some temperature difference in the two hoses would be expected, but the question would be how much difference is normal. If you suspect the heater core is stopped up with mineral deposits, here's what works for me, and I am nursing my original 20 year old, 226,000 mile heater core along. Take the short hoses off, but not at the firewall (since the heater core nipple pipes are fragile), move up to where the short hoses join into the metal pipes that run along the intake. Then take the garden hose and reverse flush the heater core. Then take some boiling water and mix with CLR and using a funnel pour the CLR and hot water into the core (carefully). Let it sit for a while (pretty much follow the instructions on the CLR container) and then flush. Repeat this process until the water flows free and clear. Note: This process could cause your heater core to leak if it is weak. As for me, it works well enough that it's worth the risk and a lot easier than replacing the core !

4G-KDMP · Nov 27, 2009

jimspinnin said:
Well, I have had the car almost 3 years and the AC and Heat never worked since I had it. It sat for some time and finally this summer I replaced a bunch of stuff on it to get into good running condition. I want to continue to drive it as long as there is no snow on the ground and we don't usually get too much but it gets cold as all hell.
I checked the two hoses today and both are connected. The one on the driver side seems hotter than the one on the passenger side. It is warm, just does not seem to be as hot.

Do you have a thermostat, and are you sure it's working?

4G-KDMP · Nov 27, 2009

I was on another site and saw where you had posted

it is getting up to normal operating temp on the temp gauge.

so disregard the ^^

jimspinnin · Nov 29, 2009

I am going to replace the thermostat when I get back from vacation, that was not one of the things I replaced.

jimspinnin · Nov 29, 2009

I checked the 2 hoses again today since it is actually a nice day and both hoses were pretty hott.

BlackGT89 · Nov 29, 2009

jimspinnin said:
I checked the 2 hoses again today since it is actually a nice day and both hoses were pretty hott.

That's cool, I mean HOT !

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